patch, 15 partssequencer: refactor functions working on a todo_list

sequencer.c, sequencer.h

diff --git a/sequencer.c b/sequencer.c
index ed798b95d1..bb8ca2477f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1443,31 +1443,6 @@ static int allow_empty(struct replay_opts *opts, struct commit *commit)
 		return 1;
 }
 
-/*
- * Note that ordering matters in this enum. Not only must it match the mapping
- * below, it is also divided into several sections that matter.  When adding
- * new commands, make sure you add it in the right section.
- */
-enum todo_command {
-	/* commands that handle commits */
-	TODO_PICK = 0,
-	TODO_REVERT,
-	TODO_EDIT,
-	TODO_REWORD,
-	TODO_FIXUP,
-	TODO_SQUASH,
-	/* commands that do something else than handling a single commit */
-	TODO_EXEC,
-	TODO_LABEL,
-	TODO_RESET,
-	TODO_MERGE,
-	/* commands that do nothing but are counted for reporting progress */
-	TODO_NOOP,
-	TODO_DROP,
-	/* comments (not counted for reporting progress) */
-	TODO_COMMENT
-};
-
 static struct {
 	char c;
 	const char *str;
@@ -1937,26 +1912,7 @@ enum todo_item_flags {
 	TODO_EDIT_MERGE_MSG = 1
 };
 
-struct todo_item {
-	enum todo_command command;
-	struct commit *commit;
-	unsigned int flags;
-	const char *arg;
-	int arg_len;
-	size_t offset_in_buf;
-};
-
-struct todo_list {
-	struct strbuf buf;
-	struct todo_item *items;
-	int nr, alloc, current;
-	int done_nr, total_nr;
-	struct stat_data stat;
-};
-
-#define TODO_LIST_INIT { STRBUF_INIT }
-
-static void todo_list_release(struct todo_list *todo_list)
+void todo_list_release(struct todo_list *todo_list)
 {
 	strbuf_release(&todo_list->buf);
 	FREE_AND_NULL(todo_list->items);
@@ -2057,7 +2013,7 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 	return !item->commit;
 }
 
-static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
+int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list)
 {
 	struct todo_item *item;
 	char *p = buf, *next_p;
@@ -2152,7 +2108,7 @@ static int read_populate_todo(struct todo_list *todo_list,
 		return error(_("could not stat '%s'"), todo_file);
 	fill_stat_data(&todo_list->stat, &st);
 
-	res = parse_insn_buffer(todo_list->buf.buf, todo_list);
+	res = todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list);
 	if (res) {
 		if (is_rebase_i(opts))
 			return error(_("please fix this using "
@@ -2183,7 +2139,7 @@ static int read_populate_todo(struct todo_list *todo_list,
 		FILE *f = fopen_or_warn(rebase_path_msgtotal(), "w");
 
 		if (strbuf_read_file(&done.buf, rebase_path_done(), 0) > 0 &&
-				!parse_insn_buffer(done.buf.buf, &done))
+				!todo_list_parse_insn_buffer(done.buf.buf, &done))
 			todo_list->done_nr = count_commands(&done);
 		else
 			todo_list->done_nr = 0;
@@ -4429,7 +4385,7 @@ int sequencer_add_exec_commands(const char *commands)
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4485,7 +4441,7 @@ int transform_todos(unsigned flags)
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4571,7 +4527,7 @@ int check_todo_list(void)
 		goto leave_check;
 	}
 	advise_to_edit_todo = res =
-		parse_insn_buffer(todo_list.buf.buf, &todo_list);
+		todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
 
 	if (res || check_level == MISSING_COMMIT_CHECK_IGNORE)
 		goto leave_check;
@@ -4590,7 +4546,7 @@ int check_todo_list(void)
 		goto leave_check;
 	}
 	strbuf_release(&todo_file);
-	res = !!parse_insn_buffer(todo_list.buf.buf, &todo_list);
+	res = !!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
 
 	/* Find commits in git-rebase-todo.backup yet unseen */
 	for (i = todo_list.nr - 1; i >= 0; i--) {
@@ -4672,7 +4628,7 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 
 	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
 		return -1;
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
 		todo_list_release(&todo_list);
 		return -1;
 	}
@@ -4760,7 +4716,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	if (strbuf_read_file(buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(buf->buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(buf->buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4868,7 +4824,7 @@ int rearrange_squash(void)
 
 	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
 		return -1;
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
 		todo_list_release(&todo_list);
 		return -1;
 	}
diff --git a/sequencer.h b/sequencer.h
index 660cff5050..c786dee543 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -72,6 +72,54 @@ enum missing_commit_check_level {
 int write_message(const void *buf, size_t len, const char *filename,
 		  int append_eol);
 
+/*
+ * Note that ordering matters in this enum. Not only must it match the mapping
+ * of todo_command_info (in sequencer.c), it is also divided into several
+ * sections that matter.  When adding new commands, make sure you add it in the
+ * right section.
+ */
+enum todo_command {
+	/* commands that handle commits */
+	TODO_PICK = 0,
+	TODO_REVERT,
+	TODO_EDIT,
+	TODO_REWORD,
+	TODO_FIXUP,
+	TODO_SQUASH,
+	/* commands that do something else than handling a single commit */
+	TODO_EXEC,
+	TODO_LABEL,
+	TODO_RESET,
+	TODO_MERGE,
+	/* commands that do nothing but are counted for reporting progress */
+	TODO_NOOP,
+	TODO_DROP,
+	/* comments (not counted for reporting progress) */
+	TODO_COMMENT
+};
+
+struct todo_item {
+	enum todo_command command;
+	struct commit *commit;
+	unsigned int flags;
+	const char *arg;
+	int arg_len;
+	size_t offset_in_buf;
+};
+
+struct todo_list {
+	struct strbuf buf;
+	struct todo_item *items;
+	int nr, alloc, current;
+	int done_nr, total_nr;
+	struct stat_data stat;
+};
+
+#define TODO_LIST_INIT { STRBUF_INIT }
+
+int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
+void todo_list_release(struct todo_list *todo_list);
+
 /* Call this to setup defaults before parsing command line options */
 void sequencer_init_config(struct replay_opts *opts);
 int sequencer_pick_revisions(struct replay_opts *opts);

diff --git a/sequencer.c b/sequencer.c
index 0a3292d5c4..ed798b95d1 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2063,6 +2063,8 @@ static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
 	char *p = buf, *next_p;
 	int i, res = 0, fixup_okay = file_exists(rebase_path_done());
 
+	todo_list->current = todo_list->nr = 0;
+
 	for (i = 1; *p; i++, p = next_p) {
 		char *eol = strchrnul(p, '\n');
 

builtin/rebase--interactive.c, rebase-interactive.c, rebase-interactive.h, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index a2ab68ed06..ea1f93ccb6 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -255,7 +255,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = transform_todos(flags);
 		break;
 	case CHECK_TODO_LIST:
-		ret = check_todo_list();
+		ret = check_todo_list_from_file();
 		break;
 	case REARRANGE_SQUASH:
 		ret = rearrange_squash();
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 0f4119cbae..ef8540245d 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -1,8 +1,32 @@
 #include "cache.h"
 #include "commit.h"
-#include "rebase-interactive.h"
 #include "sequencer.h"
+#include "rebase-interactive.h"
 #include "strbuf.h"
+#include "commit-slab.h"
+#include "config.h"
+
+enum missing_commit_check_level {
+	MISSING_COMMIT_CHECK_IGNORE = 0,
+	MISSING_COMMIT_CHECK_WARN,
+	MISSING_COMMIT_CHECK_ERROR
+};
+
+static enum missing_commit_check_level get_missing_commit_check_level(void)
+{
+	const char *value;
+
+	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
+			!strcasecmp("ignore", value))
+		return MISSING_COMMIT_CHECK_IGNORE;
+	if (!strcasecmp("warn", value))
+		return MISSING_COMMIT_CHECK_WARN;
+	if (!strcasecmp("error", value))
+		return MISSING_COMMIT_CHECK_ERROR;
+	warning(_("unrecognized setting %s for option "
+		  "rebase.missingCommitsCheck. Ignoring."), value);
+	return MISSING_COMMIT_CHECK_IGNORE;
+}
 
 void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 		      struct strbuf *buf)
@@ -88,3 +112,83 @@ int edit_todo_list(unsigned flags)
 
 	return 0;
 }
+
+define_commit_slab(commit_seen, unsigned char);
+/*
+ * Check if the user dropped some commits by mistake
+ * Behaviour determined by rebase.missingCommitsCheck.
+ * Check if there is an unrecognized command or a
+ * bad SHA-1 in a command.
+ */
+int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo)
+{
+	enum missing_commit_check_level check_level = get_missing_commit_check_level();
+	struct strbuf missing = STRBUF_INIT;
+	int advise_to_edit_todo = 0, res = 0, i;
+	struct commit_seen commit_seen;
+
+	init_commit_seen(&commit_seen);
+
+	res = todo_list_parse_insn_buffer(old_todo->buf.buf, old_todo);
+	if (!res)
+		res = todo_list_parse_insn_buffer(new_todo->buf.buf, new_todo);
+	if (res) {
+		advise_to_edit_todo = res;
+		goto leave_check;
+	}
+
+	if (check_level == MISSING_COMMIT_CHECK_IGNORE)
+		goto leave_check;
+
+	/* Mark the commits in git-rebase-todo as seen */
+	for (i = 0; i < new_todo->nr; i++) {
+		struct commit *commit = new_todo->items[i].commit;
+		if (commit)
+			*commit_seen_at(&commit_seen, commit) = 1;
+	}
+
+	/* Find commits in git-rebase-todo.backup yet unseen */
+	for (i = old_todo->nr - 1; i >= 0; i--) {
+		struct todo_item *item = old_todo->items + i;
+		struct commit *commit = item->commit;
+		if (commit && !*commit_seen_at(&commit_seen, commit)) {
+			strbuf_addf(&missing, " - %s %.*s\n",
+				    find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV),
+				    item->arg_len, item->arg);
+			*commit_seen_at(&commit_seen, commit) = 1;
+		}
+	}
+
+	/* Warn about missing commits */
+	if (!missing.len)
+		goto leave_check;
+
+	if (check_level == MISSING_COMMIT_CHECK_ERROR)
+		advise_to_edit_todo = res = 1;
+
+	fprintf(stderr,
+		_("Warning: some commits may have been dropped accidentally.\n"
+		"Dropped commits (newer to older):\n"));
+
+	/* Make the list user-friendly and display */
+	fputs(missing.buf, stderr);
+	strbuf_release(&missing);
+
+	fprintf(stderr, _("To avoid this message, use \"drop\" to "
+		"explicitly remove a commit.\n\n"
+		"Use 'git config rebase.missingCommitsCheck' to change "
+		"the level of warnings.\n"
+		"The possible behaviours are: ignore, warn, error.\n\n"));
+
+leave_check:
+	clear_commit_seen(&commit_seen);
+
+	if (advise_to_edit_todo)
+		fprintf(stderr,
+			_("You can fix this with 'git rebase --edit-todo' "
+			  "and then run 'git rebase --continue'.\n"
+			  "Or you can abort the rebase with 'git rebase"
+			  " --abort'.\n"));
+
+	return res;
+}
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 971da03776..6bc7bc315d 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -4,5 +4,6 @@
 void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 		      struct strbuf *buf);
 int edit_todo_list(unsigned flags);
+int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index bb8ca2477f..8dda61927c 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4487,111 +4487,26 @@ int transform_todos(unsigned flags)
 	return i;
 }
 
-enum missing_commit_check_level get_missing_commit_check_level(void)
+int check_todo_list_from_file(void)
 {
-	const char *value;
-
-	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
-			!strcasecmp("ignore", value))
-		return MISSING_COMMIT_CHECK_IGNORE;
-	if (!strcasecmp("warn", value))
-		return MISSING_COMMIT_CHECK_WARN;
-	if (!strcasecmp("error", value))
-		return MISSING_COMMIT_CHECK_ERROR;
-	warning(_("unrecognized setting %s for option "
-		  "rebase.missingCommitsCheck. Ignoring."), value);
-	return MISSING_COMMIT_CHECK_IGNORE;
-}
-
-define_commit_slab(commit_seen, unsigned char);
-/*
- * Check if the user dropped some commits by mistake
- * Behaviour determined by rebase.missingCommitsCheck.
- * Check if there is an unrecognized command or a
- * bad SHA-1 in a command.
- */
-int check_todo_list(void)
-{
-	enum missing_commit_check_level check_level = get_missing_commit_check_level();
-	struct strbuf todo_file = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf missing = STRBUF_INIT;
-	int advise_to_edit_todo = 0, res = 0, i;
-	struct commit_seen commit_seen;
-
-	init_commit_seen(&commit_seen);
+	struct todo_list old_todo = TODO_LIST_INIT, new_todo = TODO_LIST_INIT;
+	int res = 0;
 
-	strbuf_addstr(&todo_file, rebase_path_todo());
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
+	if (strbuf_read_file_or_whine(&new_todo.buf, rebase_path_todo()) < 0) {
 		res = -1;
-		goto leave_check;
-	}
-	advise_to_edit_todo = res =
-		todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-
-	if (res || check_level == MISSING_COMMIT_CHECK_IGNORE)
-		goto leave_check;
-
-	/* Mark the commits in git-rebase-todo as seen */
-	for (i = 0; i < todo_list.nr; i++) {
-		struct commit *commit = todo_list.items[i].commit;
-		if (commit)
-			*commit_seen_at(&commit_seen, commit) = 1;
+		goto out;
 	}
 
-	todo_list_release(&todo_list);
-	strbuf_addstr(&todo_file, ".backup");
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
+	if (strbuf_read_file_or_whine(&old_todo.buf, rebase_path_todo_backup()) < 0) {
 		res = -1;
-		goto leave_check;
-	}
-	strbuf_release(&todo_file);
-	res = !!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-
-	/* Find commits in git-rebase-todo.backup yet unseen */
-	for (i = todo_list.nr - 1; i >= 0; i--) {
-		struct todo_item *item = todo_list.items + i;
-		struct commit *commit = item->commit;
-		if (commit && !*commit_seen_at(&commit_seen, commit)) {
-			strbuf_addf(&missing, " - %s %.*s\n",
-				    short_commit_name(commit),
-				    item->arg_len, item->arg);
-			*commit_seen_at(&commit_seen, commit) = 1;
-		}
+		goto out;
 	}
 
-	/* Warn about missing commits */
-	if (!missing.len)
-		goto leave_check;
-
-	if (check_level == MISSING_COMMIT_CHECK_ERROR)
-		advise_to_edit_todo = res = 1;
+	res = todo_list_check(&old_todo, &new_todo);
 
-	fprintf(stderr,
-		_("Warning: some commits may have been dropped accidentally.\n"
-		"Dropped commits (newer to older):\n"));
-
-	/* Make the list user-friendly and display */
-	fputs(missing.buf, stderr);
-	strbuf_release(&missing);
-
-	fprintf(stderr, _("To avoid this message, use \"drop\" to "
-		"explicitly remove a commit.\n\n"
-		"Use 'git config rebase.missingCommitsCheck' to change "
-		"the level of warnings.\n"
-		"The possible behaviours are: ignore, warn, error.\n\n"));
-
-leave_check:
-	clear_commit_seen(&commit_seen);
-	strbuf_release(&todo_file);
-	todo_list_release(&todo_list);
-
-	if (advise_to_edit_todo)
-		fprintf(stderr,
-			_("You can fix this with 'git rebase --edit-todo' "
-			  "and then run 'git rebase --continue'.\n"
-			  "Or you can abort the rebase with 'git rebase"
-			  " --abort'.\n"));
+out:
+	todo_list_release(&old_todo);
+	todo_list_release(&new_todo);
 
 	return res;
 }
@@ -4769,7 +4684,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_release(&todo_list);
 
-	if (check_todo_list()) {
+	if (check_todo_list_from_file()) {
 		checkout_onto(opts, onto_name, onto, orig_head);
 		return -1;
 	}
diff --git a/sequencer.h b/sequencer.h
index c786dee543..fb8b85bf9e 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -63,12 +63,6 @@ struct replay_opts {
 };
 #define REPLAY_OPTS_INIT { .action = -1, .current_fixups = STRBUF_INIT }
 
-enum missing_commit_check_level {
-	MISSING_COMMIT_CHECK_IGNORE = 0,
-	MISSING_COMMIT_CHECK_WARN,
-	MISSING_COMMIT_CHECK_ERROR
-};
-
 int write_message(const void *buf, size_t len, const char *filename,
 		  int append_eol);
 
@@ -142,8 +136,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 int sequencer_add_exec_commands(const char *command);
 int transform_todos(unsigned flags);
-enum missing_commit_check_level get_missing_commit_check_level(void);
-int check_todo_list(void);
+int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,

diff --git a/sequencer.c b/sequencer.c
index 8dda61927c..6d998f21a4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4370,34 +4370,21 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 	return 0;
 }
 
-/*
- * Add commands after pick and (series of) squash/fixup commands
- * in the todo list.
- */
-int sequencer_add_exec_commands(const char *commands)
+static void todo_list_add_exec_commands(struct todo_list *todo_list,
+					const char *commands)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf *buf = &todo_list.buf;
+	struct strbuf *buf = &todo_list->buf;
 	size_t offset = 0, commands_len = strlen(commands);
 	int i, insert;
 
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
 	/*
 	 * Insert <commands> after every pick. Here, fixup/squash chains
 	 * are considered part of the pick, so we insert the commands *after*
 	 * those chains if there are any.
 	 */
 	insert = -1;
-	for (i = 0; i < todo_list.nr; i++) {
-		enum todo_command command = todo_list.items[i].command;
+	for (i = 0; i < todo_list->nr; i++) {
+		enum todo_command command = todo_list->items[i].command;
 
 		if (insert >= 0) {
 			/* skip fixup/squash chains */
@@ -4408,7 +4395,7 @@ int sequencer_add_exec_commands(const char *commands)
 				continue;
 			}
 			strbuf_insert(buf,
-				      todo_list.items[insert].offset_in_buf +
+				      todo_list->items[insert].offset_in_buf +
 				      offset, commands, commands_len);
 			offset += commands_len;
 			insert = -1;
@@ -4419,15 +4406,38 @@ int sequencer_add_exec_commands(const char *commands)
 	}
 
 	/* insert or append final <commands> */
-	if (insert >= 0 && insert < todo_list.nr)
-		strbuf_insert(buf, todo_list.items[insert].offset_in_buf +
+	if (insert >= 0 && insert < todo_list->nr)
+		strbuf_insert(buf, todo_list->items[insert].offset_in_buf +
 			      offset, commands, commands_len);
 	else if (insert >= 0 || !offset)
 		strbuf_add(buf, commands, commands_len);
 
-	i = write_message(buf->buf, buf->len, todo_file, 0);
+	if (todo_list_parse_insn_buffer(buf->buf, todo_list))
+		BUG("unusable todo list");}
+
+/*
+ * Add commands after pick and (series of) squash/fixup commands
+ * in the todo list.
+ */
+int sequencer_add_exec_commands(const char *commands)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_add_exec_commands(&todo_list, commands);
+	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
 	todo_list_release(&todo_list);
-	return i;
+
+	return res;
 }
 
 int transform_todos(unsigned flags)

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index eef1ff2e83..0700339f90 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -71,7 +71,6 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	const char *head_hash = NULL;
 	char *revisions = NULL, *shortrevisions = NULL;
 	struct argv_array make_script_args = ARGV_ARRAY_INIT;
-	FILE *todo_list_file;
 	struct todo_list todo_list = TODO_LIST_INIT;
 
 	if (prepare_branch_to_be_rebased(opts, switch_to))
@@ -94,14 +93,6 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (!upstream && squash_onto)
 		write_file(path_squash_onto(), "%s\n", squash_onto);
 
-	todo_list_file = fopen(rebase_path_todo(), "w");
-	if (!todo_list_file) {
-		free(revisions);
-		free(shortrevisions);
-
-		return error_errno(_("could not open %s"), rebase_path_todo());
-	}
-
 	argv_array_pushl(&make_script_args, "", revisions, NULL);
 	if (restrict_revision)
 		argv_array_push(&make_script_args, restrict_revision);
@@ -109,15 +100,13 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	ret = sequencer_make_script(&todo_list.buf,
 				    make_script_args.argc, make_script_args.argv,
 				    flags);
-	fputs(todo_list.buf.buf, todo_list_file);
-	fclose(todo_list_file);
 
 	if (ret)
 		error(_("could not generate todo list"));
 	else {
 		discard_cache();
 		ret = complete_action(opts, flags, shortrevisions, onto_name, onto,
-				      head_hash, cmd, autosquash);
+				      head_hash, cmd, autosquash, &todo_list);
 	}
 
 	free(revisions);
diff --git a/sequencer.c b/sequencer.c
index dfb8d1c974..b37935e5ab 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4624,93 +4624,89 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 	return 0;
 }
 
+static int todo_list_rearrange_squash(struct todo_list *todo_list);
+
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,
-		    unsigned autosquash)
+		    unsigned autosquash, struct todo_list *todo_list)
 {
 	const char *shortonto, *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf *buf = &(todo_list.buf);
+	struct todo_list new_todo = TODO_LIST_INIT;
+	struct strbuf *buf = &todo_list->buf;
 	struct object_id oid;
-	struct stat st;
+	int command_count;
 
 	get_oid(onto, &oid);
 	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
 
-	if (!lstat(todo_file, &st) && st.st_size == 0 &&
-	    write_message("noop\n", 5, todo_file, 0))
-		return -1;
+	if (buf->len == 0)
+		strbuf_add(buf, "noop\n", 5);
+
+	if (todo_list_parse_insn_buffer(buf->buf, todo_list))
+		BUG("unusable todo list");
 
-	if (autosquash && rearrange_squash_in_todo_file())
+	if (autosquash && todo_list_rearrange_squash(todo_list))
 		return -1;
 
 	if (cmd && *cmd)
-		sequencer_add_exec_commands(cmd);
+		todo_list_add_exec_commands(todo_list, cmd);
 
-	if (strbuf_read_file(buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(buf->buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	if (count_commands(&todo_list) == 0) {
+	command_count = count_commands(todo_list);
+	if (command_count == 0) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
 
 		return error(_("nothing to do"));
 	}
 
+	todo_list_transform(todo_list, flags | TODO_LIST_SHORTEN_IDS);
+
 	strbuf_addch(buf, '\n');
 	strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
 				      "Rebase %s onto %s (%d commands)",
-				      count_commands(&todo_list)),
-			      shortrevisions, shortonto, count_commands(&todo_list));
+				      command_count),
+			      shortrevisions, shortonto, command_count);
 	append_todo_help(0, flags & TODO_LIST_KEEP_EMPTY, buf);
 
-	if (write_message(buf->buf, buf->len, todo_file, 0)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (write_message(buf->buf, buf->len, todo_file, 0))
+		return error_errno(_("could not write '%s'"), todo_file);
 
 	if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
 		return error(_("could not copy '%s' to '%s'."), todo_file,
 			     rebase_path_todo_backup());
 
-	if (transform_todo_file(flags | TODO_LIST_SHORTEN_IDS))
-		return error(_("could not transform the todo list"));
-
-	strbuf_reset(buf);
-
-	if (launch_sequence_editor(todo_file, buf, NULL)) {
+	if (launch_sequence_editor(todo_file, &new_todo.buf, NULL)) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
 
 		return -1;
 	}
 
-	strbuf_stripspace(buf, 1);
-	if (buf->len == 0) {
+	strbuf_stripspace(&new_todo.buf, 1);
+	if (new_todo.buf.len == 0) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
+		todo_list_release(&new_todo);
 
 		return error(_("nothing to do"));
 	}
 
-	todo_list_release(&todo_list);
-
-	if (check_todo_list_from_file()) {
+	if (todo_list_check(todo_list, &new_todo)) {
 		checkout_onto(opts, onto_name, onto, orig_head);
+		todo_list_release(&new_todo);
+
 		return -1;
 	}
 
-	if (transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS)))
-		return error(_("could not transform the todo list"));
+	todo_list_transform(&new_todo, flags & ~(TODO_LIST_SHORTEN_IDS));
+
+	if (rewrite_file(todo_file, new_todo.buf.buf, new_todo.buf.len) < 0) {
+		todo_list_release(&new_todo);
+		return error_errno(_("could not write '%s'"), todo_file);
+	}
+
+	todo_list_release(&new_todo);
 
 	if (opts->allow_ff && skip_unnecessary_picks(&oid))
 		return error(_("could not skip unnecessary pick commands"));
diff --git a/sequencer.h b/sequencer.h
index 21d9ba09ab..5bd3b79282 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -141,7 +141,7 @@ int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,
-		    unsigned autosquash);
+		    unsigned autosquash, struct todo_list *todo_list);
 int rearrange_squash_in_todo_file(void);
 
 extern const char sign_off_header[];

diff --git a/rebase-interactive.c b/rebase-interactive.c
index 7c7f720a3d..f42d48e192 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -78,39 +78,37 @@ void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 
 int edit_todo_list(unsigned flags)
 {
-	struct strbuf buf = STRBUF_INIT;
 	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
 
-	if (strbuf_read_file(&buf, todo_file, 0) < 0)
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
 
-	strbuf_stripspace(&buf, 1);
-	if (write_message(buf.buf, buf.len, todo_file, 0)) {
-		strbuf_release(&buf);
-		return -1;
-	}
-
-	strbuf_release(&buf);
+	strbuf_stripspace(&todo_list.buf, 1);
+	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
+		todo_list_transform(&todo_list, flags | TODO_LIST_SHORTEN_IDS);
 
-	transform_todo_file(flags | TODO_LIST_SHORTEN_IDS);
-
-	if (strbuf_read_file(&buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
+	append_todo_help(1, 0, &todo_list.buf);
 
-	append_todo_help(1, 0, &buf);
-	if (write_message(buf.buf, buf.len, todo_file, 0)) {
-		strbuf_release(&buf);
+	if (write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0)) {
+		todo_list_release(&todo_list);
 		return -1;
 	}
 
-	strbuf_release(&buf);
-
-	if (launch_sequence_editor(todo_file, NULL, NULL))
+	strbuf_reset(&todo_list.buf);
+	if (launch_sequence_editor(todo_file, &todo_list.buf, NULL)) {
+		todo_list_release(&todo_list);
 		return -1;
+	}
 
-	transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS));
+	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_transform(&todo_list, flags & ~(TODO_LIST_SHORTEN_IDS));
+		res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
+	}
 
-	return 0;
+	todo_list_release(&todo_list);
+	return res;
 }
 
 define_commit_slab(commit_seen, unsigned char);

rebase-interactive.c, rebase-interactive.h, sequencer.c

diff --git a/rebase-interactive.c b/rebase-interactive.c
index f42d48e192..7168d56d17 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -28,7 +28,8 @@ static enum missing_commit_check_level get_missing_commit_check_level(void)
 	return MISSING_COMMIT_CHECK_IGNORE;
 }
 
-void append_todo_help(unsigned edit_todo, unsigned keep_empty,
+void append_todo_help(unsigned keep_empty, int command_count,
+		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf)
 {
 	const char *msg = _("\nCommands:\n"
@@ -47,6 +48,15 @@ void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 ".       specified). Use -c <commit> to reword the commit message.\n"
 "\n"
 "These lines can be re-ordered; they are executed from top to bottom.\n");
+	unsigned edit_todo = !(shortrevisions && shortonto);
+
+	if (!edit_todo) {
+		strbuf_addch(buf, '\n');
+		strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
+					      "Rebase %s onto %s (%d commands)",
+					      command_count),
+				      shortrevisions, shortonto, command_count);
+	}
 
 	strbuf_add_commented_lines(buf, msg, strlen(msg));
 
@@ -89,7 +99,7 @@ int edit_todo_list(unsigned flags)
 	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
 		todo_list_transform(&todo_list, flags | TODO_LIST_SHORTEN_IDS);
 
-	append_todo_help(1, 0, &todo_list.buf);
+	append_todo_help(flags, 0, NULL, NULL, &todo_list.buf);
 
 	if (write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0)) {
 		todo_list_release(&todo_list);
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 6bc7bc315d..61858f3a02 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -1,7 +1,8 @@
 #ifndef REBASE_INTERACTIVE_H
 #define REBASE_INTERACTIVE_H
 
-void append_todo_help(unsigned edit_todo, unsigned keep_empty,
+void append_todo_help(unsigned keep_empty, int command_count,
+		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
 int edit_todo_list(unsigned flags);
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
diff --git a/sequencer.c b/sequencer.c
index a432b64048..94d3058359 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4636,12 +4636,8 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_transform(todo_list, flags | TODO_LIST_SHORTEN_IDS);
 
-	strbuf_addch(buf, '\n');
-	strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
-				      "Rebase %s onto %s (%d commands)",
-				      command_count),
-			      shortrevisions, shortonto, command_count);
-	append_todo_help(0, flags & TODO_LIST_KEEP_EMPTY, buf);
+	append_todo_help(flags & TODO_LIST_KEEP_EMPTY, command_count,
+			 shortrevisions, shortonto, buf);
 
 	if (write_message(buf->buf, buf->len, todo_file, 0))
 		return error_errno(_("could not write '%s'"), todo_file);

builtin/rebase--interactive.c, rebase-interactive.c, rebase-interactive.h, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 0700339f90..264e940b47 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -13,6 +13,26 @@ static GIT_PATH_FUNC(path_state_dir, "rebase-merge/")
 static GIT_PATH_FUNC(path_squash_onto, "rebase-merge/squash-onto")
 static GIT_PATH_FUNC(path_interactive, "rebase-merge/interactive")
 
+static int edit_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT,
+		new_todo = TODO_LIST_INIT;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	strbuf_stripspace(&todo_list.buf, 1);
+	if (!edit_todo_list(&todo_list, &new_todo, flags, 0, NULL, NULL) &&
+	    write_message(new_todo.buf.buf, new_todo.buf.len, todo_file, 0) < 0)
+		return error_errno(_("could not write '%s'"), todo_file);
+
+	todo_list_release(&todo_list);
+	todo_list_release(&new_todo);
+
+	return 0;
+}
+
 static int get_revision_ranges(const char *upstream, const char *onto,
 			       const char **head_hash,
 			       char **revisions, char **shortrevisions)
@@ -231,7 +251,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		break;
 	}
 	case EDIT_TODO:
-		ret = edit_todo_list(flags);
+		ret = edit_todo_file(flags);
 		break;
 	case SHOW_CURRENT_PATCH: {
 		struct child_process cmd = CHILD_PROCESS_INIT;
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 7168d56d17..6ee60ac03f 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -86,39 +86,40 @@ void append_todo_help(unsigned keep_empty, int command_count,
 	}
 }
 
-int edit_todo_list(unsigned flags)
+int edit_todo_list(struct todo_list *todo_list, struct todo_list *new_todo,
+		   unsigned flags, int command_count,
+		   const char *shortrevisions, const char *shortonto)
 {
 	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	int res = 0;
+	unsigned initial = shortrevisions && shortonto;
 
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
+	if (initial || !todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
+		todo_list_transform(todo_list, flags | TODO_LIST_SHORTEN_IDS);
 
-	strbuf_stripspace(&todo_list.buf, 1);
-	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
-		todo_list_transform(&todo_list, flags | TODO_LIST_SHORTEN_IDS);
+	if (initial)
+		append_todo_help(flags & TODO_LIST_KEEP_EMPTY, command_count,
+				 shortrevisions, shortonto, &todo_list->buf);
+	else
+		append_todo_help(flags, 0, NULL, NULL, &todo_list->buf);
 
-	append_todo_help(flags, 0, NULL, NULL, &todo_list.buf);
+	if (write_message(todo_list->buf.buf, todo_list->buf.len, todo_file, 0))
+		return error_errno(_("could not write '%s''"), todo_file);
 
-	if (write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (initial && copy_file(rebase_path_todo_backup(), todo_file, 0666))
+		return error(_("could not copy '%s' to '%s'."), todo_file,
+			     rebase_path_todo_backup());
 
-	strbuf_reset(&todo_list.buf);
-	if (launch_sequence_editor(todo_file, &todo_list.buf, NULL)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (launch_sequence_editor(todo_file, &new_todo->buf, NULL))
+		return -2;
 
-	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_transform(&todo_list, flags & ~(TODO_LIST_SHORTEN_IDS));
-		res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
-	}
+	strbuf_stripspace(&new_todo->buf, 1);
+	if (initial && new_todo->buf.len == 0)
+		return -3;
 
-	todo_list_release(&todo_list);
-	return res;
+	if (!initial && !todo_list_parse_insn_buffer(new_todo->buf.buf, new_todo))
+		todo_list_transform(new_todo, flags & ~(TODO_LIST_SHORTEN_IDS));
+
+	return 0;
 }
 
 define_commit_slab(commit_seen, unsigned char);
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 61858f3a02..83cde455e6 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -4,7 +4,9 @@
 void append_todo_help(unsigned keep_empty, int command_count,
 		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
-int edit_todo_list(unsigned flags);
+int edit_todo_list(struct todo_list *todo_list, struct todo_list *new_todo,
+		   unsigned flags, int command_count,
+		   const char *shortrevisions, const char *shortonto);
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index 94d3058359..bfcbe8239b 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -55,8 +55,7 @@ static GIT_PATH_FUNC(rebase_path, "rebase-merge")
  * file and written to the tail of 'done'.
  */
 GIT_PATH_FUNC(rebase_path_todo, "rebase-merge/git-rebase-todo")
-static GIT_PATH_FUNC(rebase_path_todo_backup,
-		     "rebase-merge/git-rebase-todo.backup")
+GIT_PATH_FUNC(rebase_path_todo_backup, "rebase-merge/git-rebase-todo.backup")
 
 /*
  * The rebase command lines that have already been processed. A line
diff --git a/sequencer.h b/sequencer.h
index 5bd3b79282..fa84918c55 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -9,6 +9,7 @@ struct commit;
 const char *git_path_commit_editmsg(void);
 const char *git_path_seq_dir(void);
 const char *rebase_path_todo(void);
+const char *rebase_path_todo_backup(void);
 
 #define APPEND_SIGNOFF_DEDUP (1u << 0)
 

diff --git a/sequencer.c b/sequencer.c
index bfcbe8239b..93b9b40f66 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4608,7 +4608,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	struct todo_list new_todo = TODO_LIST_INIT;
 	struct strbuf *buf = &todo_list->buf;
 	struct object_id oid;
-	int command_count;
+	int command_count, res;
 
 	get_oid(onto, &oid);
 	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
@@ -4633,27 +4633,16 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return error(_("nothing to do"));
 	}
 
-	todo_list_transform(todo_list, flags | TODO_LIST_SHORTEN_IDS);
-
-	append_todo_help(flags & TODO_LIST_KEEP_EMPTY, command_count,
-			 shortrevisions, shortonto, buf);
-
-	if (write_message(buf->buf, buf->len, todo_file, 0))
-		return error_errno(_("could not write '%s'"), todo_file);
-
-	if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
-		return error(_("could not copy '%s' to '%s'."), todo_file,
-			     rebase_path_todo_backup());
-
-	if (launch_sequence_editor(todo_file, &new_todo.buf, NULL)) {
+	res = edit_todo_list(todo_list, &new_todo, flags,
+			     command_count, shortrevisions, shortonto);
+	if (res == -1)
+		return -1;
+	else if (res == -2) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
 
 		return -1;
-	}
-
-	strbuf_stripspace(&new_todo.buf, 1);
-	if (new_todo.buf.len == 0) {
+	} else if (res == -3) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
 		todo_list_release(&new_todo);
@@ -4668,8 +4657,6 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return -1;
 	}
 
-	todo_list_transform(&new_todo, flags & ~(TODO_LIST_SHORTEN_IDS));
-
 	if (opts->allow_ff && skip_unnecessary_picks(&new_todo, &oid)) {
 		todo_list_release(&new_todo);
 		return error(_("could not skip unnecessary pick commands"));

diff --git a/sequencer.c b/sequencer.c
index 93b9b40f66..65bf251ba5 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4421,7 +4421,7 @@ int sequencer_add_exec_commands(const char *commands)
 	int res;
 
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
+		return error_errno(_("could not read '%s'."), todo_file);
 
 	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 264e940b47..50b5c25402 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -33,6 +33,27 @@ static int edit_todo_file(unsigned flags)
 	return 0;
 }
 
+static int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_transform(&todo_list, flags);
+
+	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
+	todo_list_release(&todo_list);
+	return res;
+}
+
 static int get_revision_ranges(const char *upstream, const char *onto,
 			       const char **head_hash,
 			       char **revisions, char **shortrevisions)
diff --git a/sequencer.c b/sequencer.c
index 65bf251ba5..e837e52b64 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4485,27 +4485,6 @@ void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 		BUG("unusable todo list");
 }
 
-int transform_todo_file(unsigned flags)
-{
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	int res;
-
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	todo_list_transform(&todo_list, flags);
-
-	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
-	todo_list_release(&todo_list);
-	return res;
-}
-
 int check_todo_list_from_file(void)
 {
 	struct todo_list old_todo = TODO_LIST_INIT, new_todo = TODO_LIST_INIT;
diff --git a/sequencer.h b/sequencer.h
index fa84918c55..a4b0113206 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -137,7 +137,6 @@ int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);
-int transform_todo_file(unsigned flags);
 int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index f827e53f05..eef1ff2e83 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -71,7 +71,8 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	const char *head_hash = NULL;
 	char *revisions = NULL, *shortrevisions = NULL;
 	struct argv_array make_script_args = ARGV_ARRAY_INIT;
-	FILE *todo_list;
+	FILE *todo_list_file;
+	struct todo_list todo_list = TODO_LIST_INIT;
 
 	if (prepare_branch_to_be_rebased(opts, switch_to))
 		return -1;
@@ -93,8 +94,8 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (!upstream && squash_onto)
 		write_file(path_squash_onto(), "%s\n", squash_onto);
 
-	todo_list = fopen(rebase_path_todo(), "w");
-	if (!todo_list) {
+	todo_list_file = fopen(rebase_path_todo(), "w");
+	if (!todo_list_file) {
 		free(revisions);
 		free(shortrevisions);
 
@@ -105,10 +106,11 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (restrict_revision)
 		argv_array_push(&make_script_args, restrict_revision);
 
-	ret = sequencer_make_script(todo_list,
+	ret = sequencer_make_script(&todo_list.buf,
 				    make_script_args.argc, make_script_args.argv,
 				    flags);
-	fclose(todo_list);
+	fputs(todo_list.buf.buf, todo_list_file);
+	fclose(todo_list_file);
 
 	if (ret)
 		error(_("could not generate todo list"));
@@ -120,6 +122,7 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 
 	free(revisions);
 	free(shortrevisions);
+	todo_list_release(&todo_list);
 	argv_array_clear(&make_script_args);
 
 	return ret;
diff --git a/sequencer.c b/sequencer.c
index 30a7fe3958..dfb8d1c974 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4083,7 +4083,7 @@ static const char *label_oid(struct object_id *oid, const char *label,
 }
 
 static int make_script_with_merges(struct pretty_print_context *pp,
-				   struct rev_info *revs, FILE *out,
+				   struct rev_info *revs, struct strbuf *out,
 				   unsigned flags)
 {
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
@@ -4230,7 +4230,7 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	 * gathering commits not yet shown, reversing the list on the fly,
 	 * then outputting that list (labeling revisions as needed).
 	 */
-	fprintf(out, "%s onto\n", cmd_label);
+	strbuf_addf(out, "%s onto\n", cmd_label);
 	for (iter = tips; iter; iter = iter->next) {
 		struct commit_list *list = NULL, *iter2;
 
@@ -4240,9 +4240,9 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		entry = oidmap_get(&state.commit2label, &commit->object.oid);
 
 		if (entry)
-			fprintf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
+			strbuf_addf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
 		else
-			fprintf(out, "\n");
+			strbuf_addf(out, "\n");
 
 		while (oidset_contains(&interesting, &commit->object.oid) &&
 		       !oidset_contains(&shown, &commit->object.oid)) {
@@ -4255,8 +4255,8 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		}
 
 		if (!commit)
-			fprintf(out, "%s %s\n", cmd_reset,
-				rebase_cousins ? "onto" : "[new root]");
+			strbuf_addf(out, "%s %s\n", cmd_reset,
+				    rebase_cousins ? "onto" : "[new root]");
 		else {
 			const char *to = NULL;
 
@@ -4269,12 +4269,12 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 					       &state);
 
 			if (!to || !strcmp(to, "onto"))
-				fprintf(out, "%s onto\n", cmd_reset);
+				strbuf_addf(out, "%s onto\n", cmd_reset);
 			else {
 				strbuf_reset(&oneline);
 				pretty_print_commit(pp, commit, &oneline);
-				fprintf(out, "%s %s # %s\n",
-					cmd_reset, to, oneline.buf);
+				strbuf_addf(out, "%s %s # %s\n",
+					    cmd_reset, to, oneline.buf);
 			}
 		}
 
@@ -4283,11 +4283,11 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 			entry = oidmap_get(&commit2todo, oid);
 			/* only show if not already upstream */
 			if (entry)
-				fprintf(out, "%s\n", entry->string);
+				strbuf_addf(out, "%s\n", entry->string);
 			entry = oidmap_get(&state.commit2label, oid);
 			if (entry)
-				fprintf(out, "%s %s\n",
-					cmd_label, entry->string);
+				strbuf_addf(out, "%s %s\n",
+					    cmd_label, entry->string);
 			oidset_insert(&shown, oid);
 		}
 
@@ -4309,12 +4309,11 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	return 0;
 }
 
-int sequencer_make_script(FILE *out, int argc, const char **argv,
+int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags)
 {
 	char *format = NULL;
 	struct pretty_print_context pp = {0};
-	struct strbuf buf = STRBUF_INIT;
 	struct rev_info revs;
 	struct commit *commit;
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
@@ -4357,16 +4356,13 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 		if (!is_empty && (commit->object.flags & PATCHSAME))
 			continue;
-		strbuf_reset(&buf);
 		if (!keep_empty && is_empty)
-			strbuf_addf(&buf, "%c ", comment_line_char);
-		strbuf_addf(&buf, "%s %s ", insn,
+			strbuf_addf(out, "%c ", comment_line_char);
+		strbuf_addf(out, "%s %s ", insn,
 			    oid_to_hex(&commit->object.oid));
-		pretty_print_commit(&pp, commit, &buf);
-		strbuf_addch(&buf, '\n');
-		fputs(buf.buf, out);
+		pretty_print_commit(&pp, commit, out);
+		strbuf_addch(out, '\n');
 	}
-	strbuf_release(&buf);
 	return 0;
 }
 
diff --git a/sequencer.h b/sequencer.h
index e1faca7884..21d9ba09ab 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -132,7 +132,7 @@ int sequencer_remove_state(struct replay_opts *opts);
  * commits should be rebased onto the new base, this flag needs to be passed.
  */
 #define TODO_LIST_REBASE_COUSINS (1U << 4)
-int sequencer_make_script(FILE *out, int argc, const char **argv,
+int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);

--- a/sequencer.c
+++ b/sequencer.c
@@ -4311,7 +4311,7 @@ static int make_script_with_merges(struc
 		if (entry)
 			strbuf_addf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
 		else
-			strbuf_addf(out, "\n");
+			strbuf_addstr(out, "\n");
 
 		while (oidset_contains(&interesting, &commit->object.oid) &&
 		       !oidset_contains(&shown, &commit->object.oid)) {

diff --git a/sequencer.c b/sequencer.c
index b37935e5ab..a432b64048 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4545,38 +4545,20 @@ static int rewrite_file(const char *path, const char *buf, size_t len)
 }
 
 /* skip picking commits whose parents are unchanged */
-static int skip_unnecessary_picks(struct object_id *output_oid)
+static int skip_unnecessary_picks(struct todo_list *todo_list,
+				  struct object_id *output_oid)
 {
-	const char *todo_file = rebase_path_todo();
-	struct strbuf buf = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct object_id *parent_oid;
 	int fd, i;
 
-	if (!read_oneliner(&buf, rebase_path_onto(), 0))
-		return error(_("could not read 'onto'"));
-	if (get_oid(buf.buf, output_oid)) {
-		strbuf_release(&buf);
-		return error(_("need a HEAD to fixup"));
-	}
-	strbuf_release(&buf);
-
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
-
-	for (i = 0; i < todo_list.nr; i++) {
-		struct todo_item *item = todo_list.items + i;
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
 
 		if (item->command >= TODO_NOOP)
 			continue;
 		if (item->command != TODO_PICK)
 			break;
 		if (parse_commit(item->commit)) {
-			todo_list_release(&todo_list);
 			return error(_("could not parse commit '%s'"),
 				oid_to_hex(&item->commit->object.oid));
 		}
@@ -4590,37 +4572,29 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 		oidcpy(output_oid, &item->commit->object.oid);
 	}
 	if (i > 0) {
-		int offset = get_item_line_offset(&todo_list, i);
+		int offset = get_item_line_offset(todo_list, i);
 		const char *done_path = rebase_path_done();
 
 		fd = open(done_path, O_CREAT | O_WRONLY | O_APPEND, 0666);
 		if (fd < 0) {
 			error_errno(_("could not open '%s' for writing"),
 				    done_path);
-			todo_list_release(&todo_list);
 			return -1;
 		}
-		if (write_in_full(fd, todo_list.buf.buf, offset) < 0) {
+		if (write_in_full(fd, todo_list->buf.buf, offset) < 0) {
 			error_errno(_("could not write to '%s'"), done_path);
-			todo_list_release(&todo_list);
 			close(fd);
 			return -1;
 		}
 		close(fd);
 
-		if (rewrite_file(rebase_path_todo(), todo_list.buf.buf + offset,
-				 todo_list.buf.len - offset) < 0) {
-			todo_list_release(&todo_list);
-			return -1;
-		}
+		strbuf_splice(&todo_list->buf, 0, offset, NULL, 0);
 
-		todo_list.current = i;
-		if (is_fixup(peek_command(&todo_list, 0)))
-			record_in_rewritten(output_oid, peek_command(&todo_list, 0));
+		todo_list->current = i;
+		if (is_fixup(peek_command(todo_list, 0)))
+			record_in_rewritten(output_oid, peek_command(todo_list, 0));
 	}
 
-	todo_list_release(&todo_list);
-
 	return 0;
 }
 
@@ -4701,6 +4675,11 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_transform(&new_todo, flags & ~(TODO_LIST_SHORTEN_IDS));
 
+	if (opts->allow_ff && skip_unnecessary_picks(&new_todo, &oid)) {
+		todo_list_release(&new_todo);
+		return error(_("could not skip unnecessary pick commands"));
+	}
+
 	if (rewrite_file(todo_file, new_todo.buf.buf, new_todo.buf.len) < 0) {
 		todo_list_release(&new_todo);
 		return error_errno(_("could not write '%s'"), todo_file);
@@ -4708,12 +4687,9 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_release(&new_todo);
 
-	if (opts->allow_ff && skip_unnecessary_picks(&oid))
-		return error(_("could not skip unnecessary pick commands"));
-
 	if (checkout_onto(opts, onto_name, oid_to_hex(&oid), orig_head))
 		return -1;
-;
+
 	if (require_clean_work_tree("rebase", "", 1, 1))
 		return -1;
 

builtin/rebase--interactive.c, rebase-interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 8deef126d1..f827e53f05 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -252,7 +252,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	}
 	case SHORTEN_OIDS:
 	case EXPAND_OIDS:
-		ret = transform_todos(flags);
+		ret = transform_todo_file(flags);
 		break;
 	case CHECK_TODO_LIST:
 		ret = check_todo_list_from_file();
diff --git a/rebase-interactive.c b/rebase-interactive.c
index ef8540245d..7c7f720a3d 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -92,7 +92,7 @@ int edit_todo_list(unsigned flags)
 
 	strbuf_release(&buf);
 
-	transform_todos(flags | TODO_LIST_SHORTEN_IDS);
+	transform_todo_file(flags | TODO_LIST_SHORTEN_IDS);
 
 	if (strbuf_read_file(&buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
@@ -108,7 +108,7 @@ int edit_todo_list(unsigned flags)
 	if (launch_sequence_editor(todo_file, NULL, NULL))
 		return -1;
 
-	transform_todos(flags & ~(TODO_LIST_SHORTEN_IDS));
+	transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS));
 
 	return 0;
 }
diff --git a/sequencer.c b/sequencer.c
index 8a6176b3d0..30a7fe3958 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4440,23 +4440,13 @@ int sequencer_add_exec_commands(const char *commands)
 	return res;
 }
 
-int transform_todos(unsigned flags)
+void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct todo_item *item;
 	int i;
 
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
+	for (item = todo_list->items, i = 0; i < todo_list->nr; i++, item++) {
 		/* if the item is not a command write it and continue */
 		if (item->command >= TODO_COMMENT) {
 			strbuf_addf(&buf, "%.*s\n", item->arg_len, item->arg);
@@ -4492,9 +4482,33 @@ int transform_todos(unsigned flags)
 			strbuf_addf(&buf, " %.*s\n", item->arg_len, item->arg);
 	}
 
-	i = write_message(buf.buf, buf.len, todo_file, 0);
+	strbuf_reset(&todo_list->buf);
+	strbuf_add(&todo_list->buf, buf.buf, buf.len);
+	strbuf_release(&buf);
+
+	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
+		BUG("unusable todo list");
+}
+
+int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_transform(&todo_list, flags);
+
+	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
 	todo_list_release(&todo_list);
-	return i;
+	return res;
 }
 
 int check_todo_list_from_file(void)
@@ -4670,7 +4684,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return error(_("could not copy '%s' to '%s'."), todo_file,
 			     rebase_path_todo_backup());
 
-	if (transform_todos(flags | TODO_LIST_SHORTEN_IDS))
+	if (transform_todo_file(flags | TODO_LIST_SHORTEN_IDS))
 		return error(_("could not transform the todo list"));
 
 	strbuf_reset(buf);
@@ -4699,7 +4713,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return -1;
 	}
 
-	if (transform_todos(flags & ~(TODO_LIST_SHORTEN_IDS)))
+	if (transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS)))
 		return error(_("could not transform the todo list"));
 
 	if (opts->allow_ff && skip_unnecessary_picks(&oid))
diff --git a/sequencer.h b/sequencer.h
index 7f5668500f..e1faca7884 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -112,6 +112,7 @@ struct todo_list {
 #define TODO_LIST_INIT { STRBUF_INIT }
 
 int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
+void todo_list_transform(struct todo_list *todo_list, unsigned flags);
 void todo_list_release(struct todo_list *todo_list);
 
 /* Call this to setup defaults before parsing command line options */
@@ -135,7 +136,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);
-int transform_todos(unsigned flags);
+int transform_todo_file(unsigned flags);
 int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index ea1f93ccb6..8deef126d1 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -258,7 +258,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = check_todo_list_from_file();
 		break;
 	case REARRANGE_SQUASH:
-		ret = rearrange_squash();
+		ret = rearrange_squash_in_todo_file();
 		break;
 	case ADD_EXEC:
 		ret = sequencer_add_exec_commands(cmd);
diff --git a/sequencer.c b/sequencer.c
index 6d998f21a4..8a6176b3d0 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4632,7 +4632,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	    write_message("noop\n", 5, todo_file, 0))
 		return -1;
 
-	if (autosquash && rearrange_squash())
+	if (autosquash && rearrange_squash_in_todo_file())
 		return -1;
 
 	if (cmd && *cmd)
@@ -4738,22 +4738,13 @@ define_commit_slab(commit_todo_item, struct todo_item *);
  * message will have to be retrieved from the commit (as the oneline in the
  * script cannot be trusted) in order to normalize the autosquash arrangement.
  */
-int rearrange_squash(void)
+static int todo_list_rearrange_squash(struct todo_list *todo_list)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct hashmap subject2item;
-	int res = 0, rearranged = 0, *next, *tail, i;
+	int rearranged = 0, *next, *tail, i;
 	char **subjects;
 	struct commit_todo_item commit_todo;
 
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
-
 	init_commit_todo_item(&commit_todo);
 	/*
 	 * The hashmap maps onelines to the respective todo list index.
@@ -4765,13 +4756,13 @@ int rearrange_squash(void)
 	 * be moved to appear after the i'th.
 	 */
 	hashmap_init(&subject2item, (hashmap_cmp_fn) subject2item_cmp,
-		     NULL, todo_list.nr);
-	ALLOC_ARRAY(next, todo_list.nr);
-	ALLOC_ARRAY(tail, todo_list.nr);
-	ALLOC_ARRAY(subjects, todo_list.nr);
-	for (i = 0; i < todo_list.nr; i++) {
+		     NULL, todo_list->nr);
+	ALLOC_ARRAY(next, todo_list->nr);
+	ALLOC_ARRAY(tail, todo_list->nr);
+	ALLOC_ARRAY(subjects, todo_list->nr);
+	for (i = 0; i < todo_list->nr; i++) {
 		struct strbuf buf = STRBUF_INIT;
-		struct todo_item *item = todo_list.items + i;
+		struct todo_item *item = todo_list->items + i;
 		const char *commit_buffer, *subject, *p;
 		size_t subject_len;
 		int i2 = -1;
@@ -4784,7 +4775,6 @@ int rearrange_squash(void)
 		}
 
 		if (is_fixup(item->command)) {
-			todo_list_release(&todo_list);
 			clear_commit_todo_item(&commit_todo);
 			return error(_("the script was already rearranged."));
 		}
@@ -4819,7 +4809,7 @@ int rearrange_squash(void)
 				 *commit_todo_item_at(&commit_todo, commit2))
 				/* found by commit name */
 				i2 = *commit_todo_item_at(&commit_todo, commit2)
-					- todo_list.items;
+					- todo_list->items;
 			else {
 				/* copy can be a prefix of the commit subject */
 				for (i2 = 0; i2 < i; i2++)
@@ -4832,7 +4822,7 @@ int rearrange_squash(void)
 		}
 		if (i2 >= 0) {
 			rearranged = 1;
-			todo_list.items[i].command =
+			todo_list->items[i].command =
 				starts_with(subject, "fixup!") ?
 				TODO_FIXUP : TODO_SQUASH;
 			if (next[i2] < 0)
@@ -4852,8 +4842,8 @@ int rearrange_squash(void)
 	if (rearranged) {
 		struct strbuf buf = STRBUF_INIT;
 
-		for (i = 0; i < todo_list.nr; i++) {
-			enum todo_command command = todo_list.items[i].command;
+		for (i = 0; i < todo_list->nr; i++) {
+			enum todo_command command = todo_list->items[i].command;
 			int cur = i;
 
 			/*
@@ -4865,12 +4855,12 @@ int rearrange_squash(void)
 
 			while (cur >= 0) {
 				const char *bol =
-					get_item_line(&todo_list, cur);
+					get_item_line(todo_list, cur);
 				const char *eol =
-					get_item_line(&todo_list, cur + 1);
+					get_item_line(todo_list, cur + 1);
 
 				/* replace 'pick', by 'fixup' or 'squash' */
-				command = todo_list.items[cur].command;
+				command = todo_list->items[cur].command;
 				if (is_fixup(command)) {
 					strbuf_addstr(&buf,
 						todo_command_info[command].str);
@@ -4883,18 +4873,43 @@ int rearrange_squash(void)
 			}
 		}
 
-		res = rewrite_file(todo_file, buf.buf, buf.len);
+		strbuf_reset(&todo_list->buf);
+		strbuf_add(&todo_list->buf, buf.buf, buf.len);
 		strbuf_release(&buf);
 	}
 
 	free(next);
 	free(tail);
-	for (i = 0; i < todo_list.nr; i++)
+	for (i = 0; i < todo_list->nr; i++)
 		free(subjects[i]);
 	free(subjects);
 	hashmap_free(&subject2item, 1);
-	todo_list_release(&todo_list);
 
 	clear_commit_todo_item(&commit_todo);
+
+	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
+		BUG("unusable todo list");
+
+	return 0;
+}
+
+int rearrange_squash_in_todo_file(void)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
+		return -1;
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+		todo_list_release(&todo_list);
+		return -1;
+	}
+
+	res = todo_list_rearrange_squash(&todo_list);
+	if (!res)
+		res = rewrite_file(todo_file, todo_list.buf.buf, todo_list.buf.len);
+
+	todo_list_release(&todo_list);
 	return res;
 }
diff --git a/sequencer.h b/sequencer.h
index fb8b85bf9e..7f5668500f 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -141,7 +141,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,
 		    unsigned autosquash);
-int rearrange_squash(void);
+int rearrange_squash_in_todo_file(void);
 
 extern const char sign_off_header[];
 

diff --git a/sequencer.c b/sequencer.c
index 8dd6db5a01..9c8bd3f632 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2023,6 +2023,8 @@ static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
 	char *p = buf, *next_p;
 	int i, res = 0, fixup_okay = file_exists(rebase_path_done());
 
+	todo_list->current = todo_list->nr = 0;
+
 	for (i = 1; *p; i++, p = next_p) {
 		char *eol = strchrnul(p, '\n');
 
@@ -2036,7 +2038,10 @@ static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
 		if (parse_insn_line(item, p, eol)) {
 			res = error(_("invalid line %d: %.*s"),
 				i, (int)(eol - p), p);
-			item->command = TODO_NOOP;
+			item->command = TODO_COMMENT + 1;
+			item->arg = p;
+			item->arg_len = (int)(eol - p);
+			item->commit = NULL;
 		}
 
 		if (fixup_okay)

sequencer.c, sequencer.h

diff --git a/sequencer.c b/sequencer.c
index 9c8bd3f632..f791729271 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1401,31 +1401,6 @@ static int allow_empty(struct replay_opts *opts, struct commit *commit)
 		return 1;
 }
 
-/*
- * Note that ordering matters in this enum. Not only must it match the mapping
- * below, it is also divided into several sections that matter.  When adding
- * new commands, make sure you add it in the right section.
- */
-enum todo_command {
-	/* commands that handle commits */
-	TODO_PICK = 0,
-	TODO_REVERT,
-	TODO_EDIT,
-	TODO_REWORD,
-	TODO_FIXUP,
-	TODO_SQUASH,
-	/* commands that do something else than handling a single commit */
-	TODO_EXEC,
-	TODO_LABEL,
-	TODO_RESET,
-	TODO_MERGE,
-	/* commands that do nothing but are counted for reporting progress */
-	TODO_NOOP,
-	TODO_DROP,
-	/* comments (not counted for reporting progress) */
-	TODO_COMMENT
-};
-
 static struct {
 	char c;
 	const char *str;
@@ -1897,26 +1872,7 @@ enum todo_item_flags {
 	TODO_EDIT_MERGE_MSG = 1
 };
 
-struct todo_item {
-	enum todo_command command;
-	struct commit *commit;
-	unsigned int flags;
-	const char *arg;
-	int arg_len;
-	size_t offset_in_buf;
-};
-
-struct todo_list {
-	struct strbuf buf;
-	struct todo_item *items;
-	int nr, alloc, current;
-	int done_nr, total_nr;
-	struct stat_data stat;
-};
-
-#define TODO_LIST_INIT { STRBUF_INIT }
-
-static void todo_list_release(struct todo_list *todo_list)
+void todo_list_release(struct todo_list *todo_list)
 {
 	strbuf_release(&todo_list->buf);
 	FREE_AND_NULL(todo_list->items);
@@ -2017,7 +1973,7 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 	return !item->commit;
 }
 
-static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
+int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list)
 {
 	struct todo_item *item;
 	char *p = buf, *next_p;
@@ -2115,7 +2071,7 @@ static int read_populate_todo(struct todo_list *todo_list,
 		return error(_("could not stat '%s'"), todo_file);
 	fill_stat_data(&todo_list->stat, &st);
 
-	res = parse_insn_buffer(todo_list->buf.buf, todo_list);
+	res = todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list);
 	if (res) {
 		if (is_rebase_i(opts))
 			return error(_("please fix this using "
@@ -2146,7 +2102,7 @@ static int read_populate_todo(struct todo_list *todo_list,
 		FILE *f = fopen_or_warn(rebase_path_msgtotal(), "w");
 
 		if (strbuf_read_file(&done.buf, rebase_path_done(), 0) > 0 &&
-				!parse_insn_buffer(done.buf.buf, &done))
+				!todo_list_parse_insn_buffer(done.buf.buf, &done))
 			todo_list->done_nr = count_commands(&done);
 		else
 			todo_list->done_nr = 0;
@@ -4276,7 +4232,7 @@ int sequencer_add_exec_commands(const char *commands)
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4311,7 +4267,7 @@ int transform_todos(unsigned flags)
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4397,7 +4353,7 @@ int check_todo_list(void)
 		goto leave_check;
 	}
 	advise_to_edit_todo = res =
-		parse_insn_buffer(todo_list.buf.buf, &todo_list);
+		todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
 
 	if (res || check_level == MISSING_COMMIT_CHECK_IGNORE)
 		goto leave_check;
@@ -4416,7 +4372,7 @@ int check_todo_list(void)
 		goto leave_check;
 	}
 	strbuf_release(&todo_file);
-	res = !!parse_insn_buffer(todo_list.buf.buf, &todo_list);
+	res = !!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
 
 	/* Find commits in git-rebase-todo.backup yet unseen */
 	for (i = todo_list.nr - 1; i >= 0; i--) {
@@ -4498,7 +4454,7 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 
 	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
 		return -1;
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
 		todo_list_release(&todo_list);
 		return -1;
 	}
@@ -4586,7 +4542,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	if (strbuf_read_file(buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(buf->buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(buf->buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4694,7 +4650,7 @@ int rearrange_squash(void)
 
 	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
 		return -1;
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
 		todo_list_release(&todo_list);
 		return -1;
 	}
diff --git a/sequencer.h b/sequencer.h
index aab280f276..cc69473bc2 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -67,6 +67,54 @@ enum missing_commit_check_level {
 int write_message(const void *buf, size_t len, const char *filename,
 		  int append_eol);
 
+/*
+ * Note that ordering matters in this enum. Not only must it match the mapping
+ * of todo_command_info (in sequencer.c), it is also divided into several
+ * sections that matter.  When adding new commands, make sure you add it in the
+ * right section.
+ */
+enum todo_command {
+	/* commands that handle commits */
+	TODO_PICK = 0,
+	TODO_REVERT,
+	TODO_EDIT,
+	TODO_REWORD,
+	TODO_FIXUP,
+	TODO_SQUASH,
+	/* commands that do something else than handling a single commit */
+	TODO_EXEC,
+	TODO_LABEL,
+	TODO_RESET,
+	TODO_MERGE,
+	/* commands that do nothing but are counted for reporting progress */
+	TODO_NOOP,
+	TODO_DROP,
+	/* comments (not counted for reporting progress) */
+	TODO_COMMENT
+};
+
+struct todo_item {
+	enum todo_command command;
+	struct commit *commit;
+	unsigned int flags;
+	const char *arg;
+	int arg_len;
+	size_t offset_in_buf;
+};
+
+struct todo_list {
+	struct strbuf buf;
+	struct todo_item *items;
+	int nr, alloc, current;
+	int done_nr, total_nr;
+	struct stat_data stat;
+};
+
+#define TODO_LIST_INIT { STRBUF_INIT }
+
+int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
+void todo_list_release(struct todo_list *todo_list);
+
 /* Call this to setup defaults before parsing command line options */
 void sequencer_init_config(struct replay_opts *opts);
 int sequencer_pick_revisions(struct replay_opts *opts);

builtin/rebase--interactive.c, rebase-interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index a2ab68ed06..abdf6126df 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -252,7 +252,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	}
 	case SHORTEN_OIDS:
 	case EXPAND_OIDS:
-		ret = transform_todos(flags);
+		ret = transform_todo_file(flags);
 		break;
 	case CHECK_TODO_LIST:
 		ret = check_todo_list();
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 0f4119cbae..49f2f549e1 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -68,7 +68,7 @@ int edit_todo_list(unsigned flags)
 
 	strbuf_release(&buf);
 
-	transform_todos(flags | TODO_LIST_SHORTEN_IDS);
+	transform_todo_file(flags | TODO_LIST_SHORTEN_IDS);
 
 	if (strbuf_read_file(&buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
@@ -84,7 +84,7 @@ int edit_todo_list(unsigned flags)
 	if (launch_sequence_editor(todo_file, NULL, NULL))
 		return -1;
 
-	transform_todos(flags & ~(TODO_LIST_SHORTEN_IDS));
+	transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS));
 
 	return 0;
 }
diff --git a/sequencer.c b/sequencer.c
index f791729271..07296f1f57 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4256,23 +4256,13 @@ int sequencer_add_exec_commands(const char *commands)
 	return i;
 }
 
-int transform_todos(unsigned flags)
+void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct todo_item *item;
 	int i;
 
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
+	for (item = todo_list->items, i = 0; i < todo_list->nr; i++, item++) {
 		/* if the item is not a command write it and continue */
 		if (item->command >= TODO_COMMENT) {
 			strbuf_addf(&buf, "%.*s\n", item->arg_len, item->arg);
@@ -4308,9 +4298,33 @@ int transform_todos(unsigned flags)
 			strbuf_addf(&buf, " %.*s\n", item->arg_len, item->arg);
 	}
 
-	i = write_message(buf.buf, buf.len, todo_file, 0);
+	strbuf_reset(&todo_list->buf);
+	strbuf_add(&todo_list->buf, buf.buf, buf.len);
+	strbuf_release(&buf);
+
+	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
+		BUG("unusable todo list");
+}
+
+int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_transform(&todo_list, flags);
+
+	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
 	todo_list_release(&todo_list);
-	return i;
+	return res;
 }
 
 enum missing_commit_check_level get_missing_commit_check_level(void)
@@ -4571,7 +4585,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return error(_("could not copy '%s' to '%s'."), todo_file,
 			     rebase_path_todo_backup());
 
-	if (transform_todos(flags | TODO_LIST_SHORTEN_IDS))
+	if (transform_todo_file(flags | TODO_LIST_SHORTEN_IDS))
 		return error(_("could not transform the todo list"));
 
 	strbuf_reset(buf);
@@ -4600,7 +4614,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return -1;
 	}
 
-	if (transform_todos(flags & ~(TODO_LIST_SHORTEN_IDS)))
+	if (transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS)))
 		return error(_("could not transform the todo list"));
 
 	if (opts->allow_ff && skip_unnecessary_picks(&oid))
diff --git a/sequencer.h b/sequencer.h
index cc69473bc2..029d842ac5 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -113,6 +113,7 @@ struct todo_list {
 #define TODO_LIST_INIT { STRBUF_INIT }
 
 int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
+void todo_list_transform(struct todo_list *todo_list, unsigned flags);
 void todo_list_release(struct todo_list *todo_list);
 
 /* Call this to setup defaults before parsing command line options */
@@ -136,7 +137,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);
-int transform_todos(unsigned flags);
+int transform_todo_file(unsigned flags);
 enum missing_commit_check_level get_missing_commit_check_level(void);
 int check_todo_list(void);
 int complete_action(struct replay_opts *opts, unsigned flags,

sequencer.c, sequencer.h

diff --git a/sequencer.c b/sequencer.c
index 07296f1f57..0dd45677b1 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4256,24 +4256,27 @@ int sequencer_add_exec_commands(const char *commands)
 	return i;
 }
 
-void todo_list_transform(struct todo_list *todo_list, unsigned flags)
+static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,
+				int num, unsigned flags)
 {
-	struct strbuf buf = STRBUF_INIT;
 	struct todo_item *item;
-	int i;
+	int i, max = todo_list->nr;
 
-	for (item = todo_list->items, i = 0; i < todo_list->nr; i++, item++) {
+	if (num > 0 && num < max)
+		max = num;
+
+	for (item = todo_list->items, i = 0; i < max; i++, item++) {
 		/* if the item is not a command write it and continue */
 		if (item->command >= TODO_COMMENT) {
-			strbuf_addf(&buf, "%.*s\n", item->arg_len, item->arg);
+			strbuf_addf(buf, "%.*s\n", item->arg_len, item->arg);
 			continue;
 		}
 
 		/* add command to the buffer */
 		if (flags & TODO_LIST_ABBREVIATE_CMDS)
-			strbuf_addch(&buf, command_to_char(item->command));
+			strbuf_addch(buf, command_to_char(item->command));
 		else
-			strbuf_addstr(&buf, command_to_string(item->command));
+			strbuf_addstr(buf, command_to_string(item->command));
 
 		/* add commit id */
 		if (item->commit) {
@@ -4283,27 +4286,46 @@ void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 
 			if (item->command == TODO_MERGE) {
 				if (item->flags & TODO_EDIT_MERGE_MSG)
-					strbuf_addstr(&buf, " -c");
+					strbuf_addstr(buf, " -c");
 				else
-					strbuf_addstr(&buf, " -C");
+					strbuf_addstr(buf, " -C");
 			}
 
-			strbuf_addf(&buf, " %s", oid);
+			strbuf_addf(buf, " %s", oid);
 		}
 
 		/* add all the rest */
 		if (!item->arg_len)
-			strbuf_addch(&buf, '\n');
+			strbuf_addch(buf, '\n');
 		else
-			strbuf_addf(&buf, " %.*s\n", item->arg_len, item->arg);
+			strbuf_addf(buf, " %.*s\n", item->arg_len, item->arg);
 	}
+}
 
-	strbuf_reset(&todo_list->buf);
-	strbuf_add(&todo_list->buf, buf.buf, buf.len);
+int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
+			    const char *shortrevisions, const char *shortonto,
+			    int command_count, int append_help, int num, unsigned flags)
+{
+	int edit_todo = !(shortrevisions && shortonto), res;
+	struct strbuf buf = STRBUF_INIT;
+
+	todo_list_to_strbuf(todo_list, &buf, num, flags);
+
+	if (append_help) {
+		if (!edit_todo) {
+			strbuf_addch(&buf, '\n');
+			strbuf_commented_addf(&buf, Q_("Rebase %s onto %s (%d command)",
+						       "Rebase %s onto %s (%d commands)",
+						       command_count),
+					      shortrevisions, shortonto, command_count);
+		}
+		append_todo_help(edit_todo, flags & TODO_LIST_KEEP_EMPTY, &buf);
+	}
+
+	res = write_message(buf.buf, buf.len, file, 0);
 	strbuf_release(&buf);
 
-	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
-		BUG("unusable todo list");
+	return res;
 }
 
 int transform_todo_file(unsigned flags)
@@ -4320,9 +4342,8 @@ int transform_todo_file(unsigned flags)
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
 
-	todo_list_transform(&todo_list, flags);
-
-	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
+	res = todo_list_write_to_file(&todo_list, todo_file,
+				      NULL, NULL, 0, 0, -1, flags);
 	todo_list_release(&todo_list);
 	return res;
 }
diff --git a/sequencer.h b/sequencer.h
index 029d842ac5..a299c977fe 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -113,7 +113,9 @@ struct todo_list {
 #define TODO_LIST_INIT { STRBUF_INIT }
 
 int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
-void todo_list_transform(struct todo_list *todo_list, unsigned flags);
+int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
+			    const char *shortrevisions, const char *shortonto,
+			    int command_count, int append_help, int num, unsigned flags);
 void todo_list_release(struct todo_list *todo_list);
 
 /* Call this to setup defaults before parsing command line options */

builtin/rebase--interactive.c, rebase-interactive.c, rebase-interactive.h, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index abdf6126df..c1d87c0fe6 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -255,7 +255,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = transform_todo_file(flags);
 		break;
 	case CHECK_TODO_LIST:
-		ret = check_todo_list();
+		ret = check_todo_list_from_file();
 		break;
 	case REARRANGE_SQUASH:
 		ret = rearrange_squash();
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 49f2f549e1..9e81ecfe9f 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -1,8 +1,32 @@
 #include "cache.h"
 #include "commit.h"
-#include "rebase-interactive.h"
 #include "sequencer.h"
+#include "rebase-interactive.h"
 #include "strbuf.h"
+#include "commit-slab.h"
+#include "config.h"
+
+enum missing_commit_check_level {
+	MISSING_COMMIT_CHECK_IGNORE = 0,
+	MISSING_COMMIT_CHECK_WARN,
+	MISSING_COMMIT_CHECK_ERROR
+};
+
+static enum missing_commit_check_level get_missing_commit_check_level(void)
+{
+	const char *value;
+
+	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
+			!strcasecmp("ignore", value))
+		return MISSING_COMMIT_CHECK_IGNORE;
+	if (!strcasecmp("warn", value))
+		return MISSING_COMMIT_CHECK_WARN;
+	if (!strcasecmp("error", value))
+		return MISSING_COMMIT_CHECK_ERROR;
+	warning(_("unrecognized setting %s for option "
+		  "rebase.missingCommitsCheck. Ignoring."), value);
+	return MISSING_COMMIT_CHECK_IGNORE;
+}
 
 void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 		      struct strbuf *buf)
@@ -88,3 +112,67 @@ int edit_todo_list(unsigned flags)
 
 	return 0;
 }
+
+define_commit_slab(commit_seen, unsigned char);
+/*
+ * Check if the user dropped some commits by mistake
+ * Behaviour determined by rebase.missingCommitsCheck.
+ * Check if there is an unrecognized command or a
+ * bad SHA-1 in a command.
+ */
+int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo)
+{
+	enum missing_commit_check_level check_level = get_missing_commit_check_level();
+	struct strbuf missing = STRBUF_INIT;
+	int res = 0, i;
+	struct commit_seen commit_seen;
+
+	init_commit_seen(&commit_seen);
+
+	if (check_level == MISSING_COMMIT_CHECK_IGNORE)
+		goto leave_check;
+
+	/* Mark the commits in git-rebase-todo as seen */
+	for (i = 0; i < new_todo->nr; i++) {
+		struct commit *commit = new_todo->items[i].commit;
+		if (commit)
+			*commit_seen_at(&commit_seen, commit) = 1;
+	}
+
+	/* Find commits in git-rebase-todo.backup yet unseen */
+	for (i = old_todo->nr - 1; i >= 0; i--) {
+		struct todo_item *item = old_todo->items + i;
+		struct commit *commit = item->commit;
+		if (commit && !*commit_seen_at(&commit_seen, commit)) {
+			strbuf_addf(&missing, " - %s %.*s\n",
+				    find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV),
+				    item->arg_len, item->arg);
+			*commit_seen_at(&commit_seen, commit) = 1;
+		}
+	}
+
+	/* Warn about missing commits */
+	if (!missing.len)
+		goto leave_check;
+
+	if (check_level == MISSING_COMMIT_CHECK_ERROR)
+		res = 1;
+
+	fprintf(stderr,
+		_("Warning: some commits may have been dropped accidentally.\n"
+		"Dropped commits (newer to older):\n"));
+
+	/* Make the list user-friendly and display */
+	fputs(missing.buf, stderr);
+	strbuf_release(&missing);
+
+	fprintf(stderr, _("To avoid this message, use \"drop\" to "
+		"explicitly remove a commit.\n\n"
+		"Use 'git config rebase.missingCommitsCheck' to change "
+		"the level of warnings.\n"
+		"The possible behaviours are: ignore, warn, error.\n\n"));
+
+leave_check:
+	clear_commit_seen(&commit_seen);
+	return res;
+}
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 971da03776..6bc7bc315d 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -4,5 +4,6 @@
 void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 		      struct strbuf *buf);
 int edit_todo_list(unsigned flags);
+int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index 0dd45677b1..e12860c047 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4348,111 +4348,37 @@ int transform_todo_file(unsigned flags)
 	return res;
 }
 
-enum missing_commit_check_level get_missing_commit_check_level(void)
-{
-	const char *value;
-
-	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
-			!strcasecmp("ignore", value))
-		return MISSING_COMMIT_CHECK_IGNORE;
-	if (!strcasecmp("warn", value))
-		return MISSING_COMMIT_CHECK_WARN;
-	if (!strcasecmp("error", value))
-		return MISSING_COMMIT_CHECK_ERROR;
-	warning(_("unrecognized setting %s for option "
-		  "rebase.missingCommitsCheck. Ignoring."), value);
-	return MISSING_COMMIT_CHECK_IGNORE;
-}
+static const char edit_todo_list_advice[] =
+N_("You can fix this with 'git rebase --edit-todo' "
+"and then run 'git rebase --continue'.\n"
+"Or you can abort the rebase with 'git rebase"
+" --abort'.\n");
 
-define_commit_slab(commit_seen, unsigned char);
-/*
- * Check if the user dropped some commits by mistake
- * Behaviour determined by rebase.missingCommitsCheck.
- * Check if there is an unrecognized command or a
- * bad SHA-1 in a command.
- */
-int check_todo_list(void)
+int check_todo_list_from_file(void)
 {
-	enum missing_commit_check_level check_level = get_missing_commit_check_level();
-	struct strbuf todo_file = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf missing = STRBUF_INIT;
-	int advise_to_edit_todo = 0, res = 0, i;
-	struct commit_seen commit_seen;
-
-	init_commit_seen(&commit_seen);
+	struct todo_list old_todo = TODO_LIST_INIT, new_todo = TODO_LIST_INIT;
+	int res = 0;
 
-	strbuf_addstr(&todo_file, rebase_path_todo());
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
+	if (strbuf_read_file_or_whine(&new_todo.buf, rebase_path_todo()) < 0) {
 		res = -1;
-		goto leave_check;
-	}
-	advise_to_edit_todo = res =
-		todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-
-	if (res || check_level == MISSING_COMMIT_CHECK_IGNORE)
-		goto leave_check;
-
-	/* Mark the commits in git-rebase-todo as seen */
-	for (i = 0; i < todo_list.nr; i++) {
-		struct commit *commit = todo_list.items[i].commit;
-		if (commit)
-			*commit_seen_at(&commit_seen, commit) = 1;
+		goto out;
 	}
 
-	todo_list_release(&todo_list);
-	strbuf_addstr(&todo_file, ".backup");
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
+	if (strbuf_read_file_or_whine(&old_todo.buf, rebase_path_todo_backup()) < 0) {
 		res = -1;
-		goto leave_check;
-	}
-	strbuf_release(&todo_file);
-	res = !!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-
-	/* Find commits in git-rebase-todo.backup yet unseen */
-	for (i = todo_list.nr - 1; i >= 0; i--) {
-		struct todo_item *item = todo_list.items + i;
-		struct commit *commit = item->commit;
-		if (commit && !*commit_seen_at(&commit_seen, commit)) {
-			strbuf_addf(&missing, " - %s %.*s\n",
-				    short_commit_name(commit),
-				    item->arg_len, item->arg);
-			*commit_seen_at(&commit_seen, commit) = 1;
-		}
+		goto out;
 	}
 
-	/* Warn about missing commits */
-	if (!missing.len)
-		goto leave_check;
-
-	if (check_level == MISSING_COMMIT_CHECK_ERROR)
-		advise_to_edit_todo = res = 1;
-
-	fprintf(stderr,
-		_("Warning: some commits may have been dropped accidentally.\n"
-		"Dropped commits (newer to older):\n"));
-
-	/* Make the list user-friendly and display */
-	fputs(missing.buf, stderr);
-	strbuf_release(&missing);
-
-	fprintf(stderr, _("To avoid this message, use \"drop\" to "
-		"explicitly remove a commit.\n\n"
-		"Use 'git config rebase.missingCommitsCheck' to change "
-		"the level of warnings.\n"
-		"The possible behaviours are: ignore, warn, error.\n\n"));
-
-leave_check:
-	clear_commit_seen(&commit_seen);
-	strbuf_release(&todo_file);
-	todo_list_release(&todo_list);
-
-	if (advise_to_edit_todo)
-		fprintf(stderr,
-			_("You can fix this with 'git rebase --edit-todo' "
-			  "and then run 'git rebase --continue'.\n"
-			  "Or you can abort the rebase with 'git rebase"
-			  " --abort'.\n"));
+	res = todo_list_parse_insn_buffer(old_todo.buf.buf, &old_todo);
+	if (!res)
+		res = todo_list_parse_insn_buffer(new_todo.buf.buf, &new_todo);
+	if (!res)
+		res = todo_list_check(&old_todo, &new_todo);
+	if (res)
+		fprintf(stderr, _(edit_todo_list_advice));
+out:
+	todo_list_release(&old_todo);
+	todo_list_release(&new_todo);
 
 	return res;
 }
@@ -4630,7 +4556,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_release(&todo_list);
 
-	if (check_todo_list()) {
+	if (check_todo_list_from_file()) {
 		checkout_onto(opts, onto_name, onto, orig_head);
 		return -1;
 	}
diff --git a/sequencer.h b/sequencer.h
index a299c977fe..e203930084 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -58,12 +58,6 @@ struct replay_opts {
 };
 #define REPLAY_OPTS_INIT { .action = -1, .current_fixups = STRBUF_INIT }
 
-enum missing_commit_check_level {
-	MISSING_COMMIT_CHECK_IGNORE = 0,
-	MISSING_COMMIT_CHECK_WARN,
-	MISSING_COMMIT_CHECK_ERROR
-};
-
 int write_message(const void *buf, size_t len, const char *filename,
 		  int append_eol);
 
@@ -140,8 +134,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 int sequencer_add_exec_commands(const char *command);
 int transform_todo_file(unsigned flags);
-enum missing_commit_check_level get_missing_commit_check_level(void);
-int check_todo_list(void);
+int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,

diff --git a/sequencer.c b/sequencer.c
index e12860c047..12a3efeca8 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4216,6 +4216,50 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 	return 0;
 }
 
+static void todo_list_add_exec_commands(struct todo_list *todo_list,
+					const char *commands)
+{
+	struct strbuf *buf = &todo_list->buf;
+	const char *old_buf = buf->buf;
+	size_t commands_len = strlen(commands + strlen("exec ")) - 1;
+	int i, first = 1, nr = 0, alloc = 0;
+	struct todo_item *items = NULL,
+		base_item = {TODO_EXEC, NULL, 0, 0, commands_len, 0};
+
+	strbuf_addstr(buf, commands);
+	base_item.offset_in_buf = buf->len - commands_len - 1;
+	base_item.arg = buf->buf + base_item.offset_in_buf;
+
+	/*
+	 * Insert <commands> after every pick. Here, fixup/squash chains
+	 * are considered part of the pick, so we insert the commands *after*
+	 * those chains if there are any.
+	 */
+	for (i = 0; i < todo_list->nr; i++) {
+		enum todo_command command = todo_list->items[i].command;
+		if (todo_list->items[i].arg)
+			todo_list->items[i].arg = todo_list->items[i].arg - old_buf + buf->buf;
+
+		if (command == TODO_PICK && !first) {
+			ALLOC_GROW(items, nr + 1, alloc);
+			memcpy(items + nr++, &base_item, sizeof(struct todo_item));
+		}
+
+		ALLOC_GROW(items, nr + 1, alloc);
+		memcpy(items + nr++, todo_list->items + i, sizeof(struct todo_item));
+		first = 0;
+	}
+
+	/* insert or append final <commands> */
+	ALLOC_GROW(items, nr + 1, alloc);
+	memcpy(items + nr++, &base_item, sizeof(struct todo_item));
+
+	FREE_AND_NULL(todo_list->items);
+	todo_list->items = items;
+	todo_list->nr = nr;
+	todo_list->alloc = alloc;
+}
+
 /*
  * Add commands after pick and (series of) squash/fixup commands
  * in the todo list.
@@ -4224,10 +4268,7 @@ int sequencer_add_exec_commands(const char *commands)
 {
 	const char *todo_file = rebase_path_todo();
 	struct todo_list todo_list = TODO_LIST_INIT;
-	struct todo_item *item;
-	struct strbuf *buf = &todo_list.buf;
-	size_t offset = 0, commands_len = strlen(commands);
-	int i, first;
+	int res;
 
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
@@ -4237,23 +4278,11 @@ int sequencer_add_exec_commands(const char *commands)
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
 
-	first = 1;
-	/* insert <commands> before every pick except the first one */
-	for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
-		if (item->command == TODO_PICK && !first) {
-			strbuf_insert(buf, item->offset_in_buf + offset,
-				      commands, commands_len);
-			offset += commands_len;
-		}
-		first = 0;
-	}
-
-	/* append final <commands> */
-	strbuf_add(buf, commands, commands_len);
-
-	i = write_message(buf->buf, buf->len, todo_file, 0);
+	todo_list_add_exec_commands(&todo_list, commands);
+	res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 0, -1, 0);
 	todo_list_release(&todo_list);
-	return i;
+
+	return res;
 }
 
 static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index c1d87c0fe6..f827e53f05 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -258,7 +258,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = check_todo_list_from_file();
 		break;
 	case REARRANGE_SQUASH:
-		ret = rearrange_squash();
+		ret = rearrange_squash_in_todo_file();
 		break;
 	case ADD_EXEC:
 		ret = sequencer_add_exec_commands(cmd);
diff --git a/sequencer.c b/sequencer.c
index 12a3efeca8..09e32f3e5a 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4523,7 +4523,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	    write_message("noop\n", 5, todo_file, 0))
 		return -1;
 
-	if (autosquash && rearrange_squash())
+	if (autosquash && rearrange_squash_in_todo_file())
 		return -1;
 
 	if (cmd && *cmd)
@@ -4629,21 +4629,13 @@ define_commit_slab(commit_todo_item, struct todo_item *);
  * message will have to be retrieved from the commit (as the oneline in the
  * script cannot be trusted) in order to normalize the autosquash arrangement.
  */
-int rearrange_squash(void)
+static int todo_list_rearrange_squash(struct todo_list *todo_list)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct hashmap subject2item;
-	int res = 0, rearranged = 0, *next, *tail, i;
+	int rearranged = 0, *next, *tail, i, nr = 0, alloc = 0;
 	char **subjects;
 	struct commit_todo_item commit_todo;
-
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	struct todo_item *items = NULL;
 
 	init_commit_todo_item(&commit_todo);
 	/*
@@ -4656,13 +4648,13 @@ int rearrange_squash(void)
 	 * be moved to appear after the i'th.
 	 */
 	hashmap_init(&subject2item, (hashmap_cmp_fn) subject2item_cmp,
-		     NULL, todo_list.nr);
-	ALLOC_ARRAY(next, todo_list.nr);
-	ALLOC_ARRAY(tail, todo_list.nr);
-	ALLOC_ARRAY(subjects, todo_list.nr);
-	for (i = 0; i < todo_list.nr; i++) {
+		     NULL, todo_list->nr);
+	ALLOC_ARRAY(next, todo_list->nr);
+	ALLOC_ARRAY(tail, todo_list->nr);
+	ALLOC_ARRAY(subjects, todo_list->nr);
+	for (i = 0; i < todo_list->nr; i++) {
 		struct strbuf buf = STRBUF_INIT;
-		struct todo_item *item = todo_list.items + i;
+		struct todo_item *item = todo_list->items + i;
 		const char *commit_buffer, *subject, *p;
 		size_t subject_len;
 		int i2 = -1;
@@ -4675,7 +4667,6 @@ int rearrange_squash(void)
 		}
 
 		if (is_fixup(item->command)) {
-			todo_list_release(&todo_list);
 			clear_commit_todo_item(&commit_todo);
 			return error(_("the script was already rearranged."));
 		}
@@ -4710,7 +4701,7 @@ int rearrange_squash(void)
 				 *commit_todo_item_at(&commit_todo, commit2))
 				/* found by commit name */
 				i2 = *commit_todo_item_at(&commit_todo, commit2)
-					- todo_list.items;
+					- todo_list->items;
 			else {
 				/* copy can be a prefix of the commit subject */
 				for (i2 = 0; i2 < i; i2++)
@@ -4723,7 +4714,7 @@ int rearrange_squash(void)
 		}
 		if (i2 >= 0) {
 			rearranged = 1;
-			todo_list.items[i].command =
+			todo_list->items[i].command =
 				starts_with(subject, "fixup!") ?
 				TODO_FIXUP : TODO_SQUASH;
 			if (next[i2] < 0)
@@ -4741,10 +4732,8 @@ int rearrange_squash(void)
 	}
 
 	if (rearranged) {
-		struct strbuf buf = STRBUF_INIT;
-
-		for (i = 0; i < todo_list.nr; i++) {
-			enum todo_command command = todo_list.items[i].command;
+		for (i = 0; i < todo_list->nr; i++) {
+			enum todo_command command = todo_list->items[i].command;
 			int cur = i;
 
 			/*
@@ -4755,37 +4744,47 @@ int rearrange_squash(void)
 				continue;
 
 			while (cur >= 0) {
-				const char *bol =
-					get_item_line(&todo_list, cur);
-				const char *eol =
-					get_item_line(&todo_list, cur + 1);
-
-				/* replace 'pick', by 'fixup' or 'squash' */
-				command = todo_list.items[cur].command;
-				if (is_fixup(command)) {
-					strbuf_addstr(&buf,
-						todo_command_info[command].str);
-					bol += strcspn(bol, " \t");
-				}
-
-				strbuf_add(&buf, bol, eol - bol);
-
+				ALLOC_GROW(items, nr + 1, alloc);
+				memcpy(items + nr++, todo_list->items + cur, sizeof(struct todo_item));
 				cur = next[cur];
 			}
 		}
 
-		res = rewrite_file(todo_file, buf.buf, buf.len);
-		strbuf_release(&buf);
+		FREE_AND_NULL(todo_list->items);
+		todo_list->items = items;
+		todo_list->nr = nr;
+		todo_list->alloc = alloc;
 	}
 
 	free(next);
 	free(tail);
-	for (i = 0; i < todo_list.nr; i++)
+	for (i = 0; i < todo_list->nr; i++)
 		free(subjects[i]);
 	free(subjects);
 	hashmap_free(&subject2item, 1);
-	todo_list_release(&todo_list);
 
 	clear_commit_todo_item(&commit_todo);
+
+	return 0;
+}
+
+int rearrange_squash_in_todo_file(void)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
+		return -1;
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+		todo_list_release(&todo_list);
+		return -1;
+	}
+
+	res = todo_list_rearrange_squash(&todo_list);
+	if (!res)
+		res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 0, -1, 0);
+
+	todo_list_release(&todo_list);
 	return res;
 }
diff --git a/sequencer.h b/sequencer.h
index e203930084..0c8074cab0 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -139,7 +139,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,
 		    unsigned autosquash);
-int rearrange_squash(void);
+int rearrange_squash_in_todo_file(void);
 
 extern const char sign_off_header[];
 

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index f827e53f05..eef1ff2e83 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -71,7 +71,8 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	const char *head_hash = NULL;
 	char *revisions = NULL, *shortrevisions = NULL;
 	struct argv_array make_script_args = ARGV_ARRAY_INIT;
-	FILE *todo_list;
+	FILE *todo_list_file;
+	struct todo_list todo_list = TODO_LIST_INIT;
 
 	if (prepare_branch_to_be_rebased(opts, switch_to))
 		return -1;
@@ -93,8 +94,8 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (!upstream && squash_onto)
 		write_file(path_squash_onto(), "%s\n", squash_onto);
 
-	todo_list = fopen(rebase_path_todo(), "w");
-	if (!todo_list) {
+	todo_list_file = fopen(rebase_path_todo(), "w");
+	if (!todo_list_file) {
 		free(revisions);
 		free(shortrevisions);
 
@@ -105,10 +106,11 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (restrict_revision)
 		argv_array_push(&make_script_args, restrict_revision);
 
-	ret = sequencer_make_script(todo_list,
+	ret = sequencer_make_script(&todo_list.buf,
 				    make_script_args.argc, make_script_args.argv,
 				    flags);
-	fclose(todo_list);
+	fputs(todo_list.buf.buf, todo_list_file);
+	fclose(todo_list_file);
 
 	if (ret)
 		error(_("could not generate todo list"));
@@ -120,6 +122,7 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 
 	free(revisions);
 	free(shortrevisions);
+	todo_list_release(&todo_list);
 	argv_array_clear(&make_script_args);
 
 	return ret;
diff --git a/sequencer.c b/sequencer.c
index 09e32f3e5a..94167588a2 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -3927,7 +3927,7 @@ static const char *label_oid(struct object_id *oid, const char *label,
 }
 
 static int make_script_with_merges(struct pretty_print_context *pp,
-				   struct rev_info *revs, FILE *out,
+				   struct rev_info *revs, struct strbuf *out,
 				   unsigned flags)
 {
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
@@ -4076,7 +4076,7 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	 * gathering commits not yet shown, reversing the list on the fly,
 	 * then outputting that list (labeling revisions as needed).
 	 */
-	fprintf(out, "%s onto\n", cmd_label);
+	strbuf_addf(out, "%s onto\n", cmd_label);
 	for (iter = tips; iter; iter = iter->next) {
 		struct commit_list *list = NULL, *iter2;
 
@@ -4086,9 +4086,9 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		entry = oidmap_get(&state.commit2label, &commit->object.oid);
 
 		if (entry)
-			fprintf(out, "\n# Branch %s\n", entry->string);
+			strbuf_addf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
 		else
-			fprintf(out, "\n");
+			strbuf_addch(out, '\n');
 
 		while (oidset_contains(&interesting, &commit->object.oid) &&
 		       !oidset_contains(&shown, &commit->object.oid)) {
@@ -4101,8 +4101,8 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		}
 
 		if (!commit)
-			fprintf(out, "%s %s\n", cmd_reset,
-				rebase_cousins ? "onto" : "[new root]");
+			strbuf_addf(out, "%s %s\n", cmd_reset,
+				    rebase_cousins ? "onto" : "[new root]");
 		else {
 			const char *to = NULL;
 
@@ -4115,12 +4115,12 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 					       &state);
 
 			if (!to || !strcmp(to, "onto"))
-				fprintf(out, "%s onto\n", cmd_reset);
+				strbuf_addf(out, "%s onto\n", cmd_reset);
 			else {
 				strbuf_reset(&oneline);
 				pretty_print_commit(pp, commit, &oneline);
-				fprintf(out, "%s %s # %s\n",
-					cmd_reset, to, oneline.buf);
+				strbuf_addf(out, "%s %s # %s\n",
+					    cmd_reset, to, oneline.buf);
 			}
 		}
 
@@ -4129,11 +4129,11 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 			entry = oidmap_get(&commit2todo, oid);
 			/* only show if not already upstream */
 			if (entry)
-				fprintf(out, "%s\n", entry->string);
+				strbuf_addf(out, "%s\n", entry->string);
 			entry = oidmap_get(&state.commit2label, oid);
 			if (entry)
-				fprintf(out, "%s %s\n",
-					cmd_label, entry->string);
+				strbuf_addf(out, "%s %s\n",
+					    cmd_label, entry->string);
 			oidset_insert(&shown, oid);
 		}
 
@@ -4155,12 +4155,11 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	return 0;
 }
 
-int sequencer_make_script(FILE *out, int argc, const char **argv,
+int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags)
 {
 	char *format = NULL;
 	struct pretty_print_context pp = {0};
-	struct strbuf buf = STRBUF_INIT;
 	struct rev_info revs;
 	struct commit *commit;
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
@@ -4203,16 +4202,13 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 		if (!is_empty && (commit->object.flags & PATCHSAME))
 			continue;
-		strbuf_reset(&buf);
 		if (!keep_empty && is_empty)
-			strbuf_addf(&buf, "%c ", comment_line_char);
-		strbuf_addf(&buf, "%s %s ", insn,
+			strbuf_addf(out, "%c ", comment_line_char);
+		strbuf_addf(out, "%s %s ", insn,
 			    oid_to_hex(&commit->object.oid));
-		pretty_print_commit(&pp, commit, &buf);
-		strbuf_addch(&buf, '\n');
-		fputs(buf.buf, out);
+		pretty_print_commit(&pp, commit, out);
+		strbuf_addch(out, '\n');
 	}
-	strbuf_release(&buf);
 	return 0;
 }
 
diff --git a/sequencer.h b/sequencer.h
index 0c8074cab0..5af96723e6 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -129,7 +129,7 @@ int sequencer_remove_state(struct replay_opts *opts);
  * commits should be rebased onto the new base, this flag needs to be passed.
  */
 #define TODO_LIST_REBASE_COUSINS (1U << 4)
-int sequencer_make_script(FILE *out, int argc, const char **argv,
+int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index eef1ff2e83..c07330bdff 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -71,7 +71,6 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	const char *head_hash = NULL;
 	char *revisions = NULL, *shortrevisions = NULL;
 	struct argv_array make_script_args = ARGV_ARRAY_INIT;
-	FILE *todo_list_file;
 	struct todo_list todo_list = TODO_LIST_INIT;
 
 	if (prepare_branch_to_be_rebased(opts, switch_to))
@@ -94,14 +93,6 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (!upstream && squash_onto)
 		write_file(path_squash_onto(), "%s\n", squash_onto);
 
-	todo_list_file = fopen(rebase_path_todo(), "w");
-	if (!todo_list_file) {
-		free(revisions);
-		free(shortrevisions);
-
-		return error_errno(_("could not open %s"), rebase_path_todo());
-	}
-
 	argv_array_pushl(&make_script_args, "", revisions, NULL);
 	if (restrict_revision)
 		argv_array_push(&make_script_args, restrict_revision);
@@ -109,15 +100,16 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	ret = sequencer_make_script(&todo_list.buf,
 				    make_script_args.argc, make_script_args.argv,
 				    flags);
-	fputs(todo_list.buf.buf, todo_list_file);
-	fclose(todo_list_file);
 
 	if (ret)
 		error(_("could not generate todo list"));
 	else {
 		discard_cache();
+		if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
+			BUG("unusable todo list");
+
 		ret = complete_action(opts, flags, shortrevisions, onto_name, onto,
-				      head_hash, cmd, autosquash);
+				      head_hash, cmd, autosquash, &todo_list);
 	}
 
 	free(revisions);
diff --git a/sequencer.c b/sequencer.c
index 94167588a2..1f7579328b 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4501,93 +4501,85 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 	return 0;
 }
 
+static int todo_list_rearrange_squash(struct todo_list *todo_list);
+
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,
-		    unsigned autosquash)
+		    unsigned autosquash, struct todo_list *todo_list)
 {
 	const char *shortonto, *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf *buf = &(todo_list.buf);
+	struct todo_list new_todo = TODO_LIST_INIT;
+	struct strbuf *buf = &todo_list->buf;
 	struct object_id oid;
-	struct stat st;
+	int command_count;
 
 	get_oid(onto, &oid);
 	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
 
-	if (!lstat(todo_file, &st) && st.st_size == 0 &&
-	    write_message("noop\n", 5, todo_file, 0))
-		return -1;
+	if (buf->len == 0) {
+		struct todo_item *item = append_new_todo(todo_list);
+		item->command = TODO_NOOP;
+		item->commit = NULL;
+		item->arg = NULL;
+		item->arg_len = item->flags = item->offset_in_buf = 0;
+	}
 
-	if (autosquash && rearrange_squash_in_todo_file())
+	if (autosquash && todo_list_rearrange_squash(todo_list))
 		return -1;
 
 	if (cmd && *cmd)
-		sequencer_add_exec_commands(cmd);
-
-	if (strbuf_read_file(buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(buf->buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
+		todo_list_add_exec_commands(todo_list, cmd);
 
-	if (count_commands(&todo_list) == 0) {
+	command_count = count_commands(todo_list);
+	if (command_count == 0) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
 
 		return error(_("nothing to do"));
 	}
 
-	strbuf_addch(buf, '\n');
-	strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
-				      "Rebase %s onto %s (%d commands)",
-				      count_commands(&todo_list)),
-			      shortrevisions, shortonto, count_commands(&todo_list));
-	append_todo_help(0, flags & TODO_LIST_KEEP_EMPTY, buf);
-
-	if (write_message(buf->buf, buf->len, todo_file, 0)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (todo_list_write_to_file(todo_list, todo_file,
+				    shortrevisions, shortonto, command_count,
+				    1, -1, flags | TODO_LIST_SHORTEN_IDS))
+		return error_errno(_("could not write '%s'"), todo_file);
 
 	if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
 		return error(_("could not copy '%s' to '%s'."), todo_file,
 			     rebase_path_todo_backup());
 
-	if (transform_todo_file(flags | TODO_LIST_SHORTEN_IDS))
-		return error(_("could not transform the todo list"));
-
-	strbuf_reset(buf);
-
-	if (launch_sequence_editor(todo_file, buf, NULL)) {
+	if (launch_sequence_editor(todo_file, &new_todo.buf, NULL)) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
 
 		return -1;
 	}
 
-	strbuf_stripspace(buf, 1);
-	if (buf->len == 0) {
+	strbuf_stripspace(&new_todo.buf, 1);
+	if (new_todo.buf.len == 0) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
+		todo_list_release(&new_todo);
 
 		return error(_("nothing to do"));
 	}
 
-	todo_list_release(&todo_list);
-
-	if (check_todo_list_from_file()) {
+	if (todo_list_parse_insn_buffer(new_todo.buf.buf, &new_todo) ||
+	    todo_list_check(todo_list, &new_todo)) {
+		fprintf(stderr, _(edit_todo_list_advice));
 		checkout_onto(opts, onto_name, onto, orig_head);
+		todo_list_release(&new_todo);
+
 		return -1;
 	}
 
-	if (transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS)))
-		return error(_("could not transform the todo list"));
+	if (todo_list_write_to_file(&new_todo, todo_file, NULL, NULL, 0, 0, -1,
+				    flags & ~(TODO_LIST_SHORTEN_IDS))) {
+		todo_list_release(&new_todo);
+		return error_errno(_("could not write '%s'"), todo_file);
+	}
+
+	todo_list_release(&new_todo);
 
 	if (opts->allow_ff && skip_unnecessary_picks(&oid))
 		return error(_("could not skip unnecessary pick commands"));
diff --git a/sequencer.h b/sequencer.h
index 5af96723e6..4a051e5dc9 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -138,7 +138,7 @@ int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,
-		    unsigned autosquash);
+		    unsigned autosquash, struct todo_list *todo_list);
 int rearrange_squash_in_todo_file(void);
 
 extern const char sign_off_header[];

diff --git a/sequencer.c b/sequencer.c
index 1f7579328b..7286498572 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4408,52 +4408,21 @@ int check_todo_list_from_file(void)
 	return res;
 }
 
-static int rewrite_file(const char *path, const char *buf, size_t len)
-{
-	int rc = 0;
-	int fd = open(path, O_WRONLY | O_TRUNC);
-	if (fd < 0)
-		return error_errno(_("could not open '%s' for writing"), path);
-	if (write_in_full(fd, buf, len) < 0)
-		rc = error_errno(_("could not write to '%s'"), path);
-	if (close(fd) && !rc)
-		rc = error_errno(_("could not close '%s'"), path);
-	return rc;
-}
-
 /* skip picking commits whose parents are unchanged */
-static int skip_unnecessary_picks(struct object_id *output_oid)
+static int skip_unnecessary_picks(struct todo_list *todo_list,
+				  struct object_id *output_oid)
 {
-	const char *todo_file = rebase_path_todo();
-	struct strbuf buf = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct object_id *parent_oid;
-	int fd, i;
-
-	if (!read_oneliner(&buf, rebase_path_onto(), 0))
-		return error(_("could not read 'onto'"));
-	if (get_oid(buf.buf, output_oid)) {
-		strbuf_release(&buf);
-		return error(_("need a HEAD to fixup"));
-	}
-	strbuf_release(&buf);
-
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	int i;
 
-	for (i = 0; i < todo_list.nr; i++) {
-		struct todo_item *item = todo_list.items + i;
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
 
 		if (item->command >= TODO_NOOP)
 			continue;
 		if (item->command != TODO_PICK)
 			break;
 		if (parse_commit(item->commit)) {
-			todo_list_release(&todo_list);
 			return error(_("could not parse commit '%s'"),
 				oid_to_hex(&item->commit->object.oid));
 		}
@@ -4467,37 +4436,22 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 		oidcpy(output_oid, &item->commit->object.oid);
 	}
 	if (i > 0) {
-		int offset = get_item_line_offset(&todo_list, i);
 		const char *done_path = rebase_path_done();
 
-		fd = open(done_path, O_CREAT | O_WRONLY | O_APPEND, 0666);
-		if (fd < 0) {
-			error_errno(_("could not open '%s' for writing"),
-				    done_path);
-			todo_list_release(&todo_list);
-			return -1;
-		}
-		if (write_in_full(fd, todo_list.buf.buf, offset) < 0) {
+		if (todo_list_write_to_file(todo_list, done_path, NULL, NULL, 0, 0, i, 0)) {
 			error_errno(_("could not write to '%s'"), done_path);
-			todo_list_release(&todo_list);
-			close(fd);
 			return -1;
 		}
-		close(fd);
 
-		if (rewrite_file(rebase_path_todo(), todo_list.buf.buf + offset,
-				 todo_list.buf.len - offset) < 0) {
-			todo_list_release(&todo_list);
-			return -1;
-		}
+		memmove(todo_list->items, todo_list->items + i,
+			sizeof(struct todo_item) * (todo_list->nr - i));
+		todo_list->nr -= i;
+		todo_list->current = 0;
 
-		todo_list.current = i;
-		if (is_fixup(peek_command(&todo_list, 0)))
-			record_in_rewritten(output_oid, peek_command(&todo_list, 0));
+		if (is_fixup(peek_command(todo_list, 0)))
+			record_in_rewritten(output_oid, peek_command(todo_list, 0));
 	}
 
-	todo_list_release(&todo_list);
-
 	return 0;
 }
 
@@ -4573,6 +4527,11 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return -1;
 	}
 
+	if (opts->allow_ff && skip_unnecessary_picks(&new_todo, &oid)) {
+		todo_list_release(&new_todo);
+		return error(_("could not skip unnecessary pick commands"));
+	}
+
 	if (todo_list_write_to_file(&new_todo, todo_file, NULL, NULL, 0, 0, -1,
 				    flags & ~(TODO_LIST_SHORTEN_IDS))) {
 		todo_list_release(&new_todo);
@@ -4581,12 +4540,9 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_release(&new_todo);
 
-	if (opts->allow_ff && skip_unnecessary_picks(&oid))
-		return error(_("could not skip unnecessary pick commands"));
-
 	if (checkout_onto(opts, onto_name, oid_to_hex(&oid), orig_head))
 		return -1;
-;
+
 	if (require_clean_work_tree("rebase", "", 1, 1))
 		return -1;
 

diff --git a/rebase-interactive.c b/rebase-interactive.c
index 9e81ecfe9f..b2be99a900 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -78,39 +78,33 @@ void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 
 int edit_todo_list(unsigned flags)
 {
-	struct strbuf buf = STRBUF_INIT;
 	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
 
-	if (strbuf_read_file(&buf, todo_file, 0) < 0)
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
 
-	strbuf_stripspace(&buf, 1);
-	if (write_message(buf.buf, buf.len, todo_file, 0)) {
-		strbuf_release(&buf);
+	strbuf_stripspace(&todo_list.buf, 1);
+	todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
+	if (todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 1, -1,
+				    flags | TODO_LIST_SHORTEN_IDS)) {
+		todo_list_release(&todo_list);
 		return -1;
 	}
 
-	strbuf_release(&buf);
-
-	transform_todo_file(flags | TODO_LIST_SHORTEN_IDS);
-
-	if (strbuf_read_file(&buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	append_todo_help(1, 0, &buf);
-	if (write_message(buf.buf, buf.len, todo_file, 0)) {
-		strbuf_release(&buf);
+	strbuf_reset(&todo_list.buf);
+	if (launch_sequence_editor(todo_file, &todo_list.buf, NULL)) {
+		todo_list_release(&todo_list);
 		return -1;
 	}
 
-	strbuf_release(&buf);
+	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
+		res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 0, -1,
+					      flags & ~(TODO_LIST_SHORTEN_IDS));
 
-	if (launch_sequence_editor(todo_file, NULL, NULL))
-		return -1;
-
-	transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS));
-
-	return 0;
+	todo_list_release(&todo_list);
+	return res;
 }
 
 define_commit_slab(commit_seen, unsigned char);

rebase-interactive.c, rebase-interactive.h, sequencer.c

diff --git a/rebase-interactive.c b/rebase-interactive.c
index b2be99a900..0643d54b1b 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -28,7 +28,8 @@ static enum missing_commit_check_level get_missing_commit_check_level(void)
 	return MISSING_COMMIT_CHECK_IGNORE;
 }
 
-void append_todo_help(unsigned edit_todo, unsigned keep_empty,
+void append_todo_help(unsigned keep_empty, int command_count,
+		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf)
 {
 	const char *msg = _("\nCommands:\n"
@@ -47,6 +48,15 @@ void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 ".       specified). Use -c <commit> to reword the commit message.\n"
 "\n"
 "These lines can be re-ordered; they are executed from top to bottom.\n");
+	unsigned edit_todo = !(shortrevisions && shortonto);
+
+	if (!edit_todo) {
+		strbuf_addch(buf, '\n');
+		strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
+					      "Rebase %s onto %s (%d commands)",
+					      command_count),
+				      shortrevisions, shortonto, command_count);
+	}
 
 	strbuf_add_commented_lines(buf, msg, strlen(msg));
 
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 6bc7bc315d..61858f3a02 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -1,7 +1,8 @@
 #ifndef REBASE_INTERACTIVE_H
 #define REBASE_INTERACTIVE_H
 
-void append_todo_help(unsigned edit_todo, unsigned keep_empty,
+void append_todo_help(unsigned keep_empty, int command_count,
+		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
 int edit_todo_list(unsigned flags);
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
diff --git a/sequencer.c b/sequencer.c
index 7286498572..4c664d6388 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4331,21 +4331,13 @@ int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
 			    const char *shortrevisions, const char *shortonto,
 			    int command_count, int append_help, int num, unsigned flags)
 {
-	int edit_todo = !(shortrevisions && shortonto), res;
+	int res;
 	struct strbuf buf = STRBUF_INIT;
 
 	todo_list_to_strbuf(todo_list, &buf, num, flags);
-
-	if (append_help) {
-		if (!edit_todo) {
-			strbuf_addch(&buf, '\n');
-			strbuf_commented_addf(&buf, Q_("Rebase %s onto %s (%d command)",
-						       "Rebase %s onto %s (%d commands)",
-						       command_count),
-					      shortrevisions, shortonto, command_count);
-		}
-		append_todo_help(edit_todo, flags & TODO_LIST_KEEP_EMPTY, &buf);
-	}
+	if (append_help)
+		append_todo_help(flags & TODO_LIST_KEEP_EMPTY, command_count,
+				 shortrevisions, shortonto, &buf);
 
 	res = write_message(buf.buf, buf.len, file, 0);
 	strbuf_release(&buf);

builtin/rebase--interactive.c, rebase-interactive.c, rebase-interactive.h, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index c07330bdff..0f83422aa0 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -13,6 +13,27 @@ static GIT_PATH_FUNC(path_state_dir, "rebase-merge/")
 static GIT_PATH_FUNC(path_squash_onto, "rebase-merge/squash-onto")
 static GIT_PATH_FUNC(path_interactive, "rebase-merge/interactive")
 
+static int edit_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT,
+		new_todo = TODO_LIST_INIT;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	strbuf_stripspace(&todo_list.buf, 1);
+	if (!edit_todo_list(&todo_list, &new_todo, flags, 0, NULL, NULL) &&
+	    todo_list_write_to_file(&new_todo, todo_file, NULL, NULL, 0, 0, -1,
+				    flags & ~(TODO_LIST_SHORTEN_IDS)) < 0)
+		return error_errno(_("could not write '%s'"), todo_file);
+
+	todo_list_release(&todo_list);
+	todo_list_release(&new_todo);
+
+	return 0;
+}
+
 static int get_revision_ranges(const char *upstream, const char *onto,
 			       const char **head_hash,
 			       char **revisions, char **shortrevisions)
@@ -234,7 +255,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		break;
 	}
 	case EDIT_TODO:
-		ret = edit_todo_list(flags);
+		ret = edit_todo_file(flags);
 		break;
 	case SHOW_CURRENT_PATCH: {
 		struct child_process cmd = CHILD_PROCESS_INIT;
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 0643d54b1b..d7a0818ac9 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -86,35 +86,37 @@ void append_todo_help(unsigned keep_empty, int command_count,
 	}
 }
 
-int edit_todo_list(unsigned flags)
+int edit_todo_list(struct todo_list *todo_list, struct todo_list *new_todo,
+		   unsigned flags, int command_count,
+		   const char *shortrevisions, const char *shortonto)
 {
 	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	int res = 0;
-
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	strbuf_stripspace(&todo_list.buf, 1);
-	todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-	if (todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 1, -1,
-				    flags | TODO_LIST_SHORTEN_IDS)) {
-		todo_list_release(&todo_list);
-		return -1;
+	unsigned initial = shortrevisions && shortonto;
+
+	if (initial) {
+		todo_list_write_to_file(todo_list, todo_file, shortrevisions, shortonto,
+					0, 1, -1, flags | TODO_LIST_SHORTEN_IDS);
+
+		if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
+			return error(_("could not copy '%s' to '%s'."), todo_file,
+				     rebase_path_todo_backup());
+	} else {
+		todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list);
+		todo_list_write_to_file(todo_list, todo_file, NULL, NULL, 0, 1, -1,
+					flags | TODO_LIST_SHORTEN_IDS);
 	}
 
-	strbuf_reset(&todo_list.buf);
-	if (launch_sequence_editor(todo_file, &todo_list.buf, NULL)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (launch_sequence_editor(todo_file, &new_todo->buf, NULL))
+		return -2;
 
-	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
-		res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 0, -1,
-					      flags & ~(TODO_LIST_SHORTEN_IDS));
+	strbuf_stripspace(&new_todo->buf, 1);
+	if (initial && new_todo->buf.len == 0)
+		return -3;
 
-	todo_list_release(&todo_list);
-	return res;
+	if (!initial)
+		todo_list_parse_insn_buffer(new_todo->buf.buf, new_todo);
+
+	return 0;
 }
 
 define_commit_slab(commit_seen, unsigned char);
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 61858f3a02..83cde455e6 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -4,7 +4,9 @@
 void append_todo_help(unsigned keep_empty, int command_count,
 		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
-int edit_todo_list(unsigned flags);
+int edit_todo_list(struct todo_list *todo_list, struct todo_list *new_todo,
+		   unsigned flags, int command_count,
+		   const char *shortrevisions, const char *shortonto);
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index 4c664d6388..a03505f582 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -54,8 +54,7 @@ static GIT_PATH_FUNC(rebase_path, "rebase-merge")
  * file and written to the tail of 'done'.
  */
 GIT_PATH_FUNC(rebase_path_todo, "rebase-merge/git-rebase-todo")
-static GIT_PATH_FUNC(rebase_path_todo_backup,
-		     "rebase-merge/git-rebase-todo.backup")
+GIT_PATH_FUNC(rebase_path_todo_backup, "rebase-merge/git-rebase-todo.backup")
 
 /*
  * The rebase command lines that have already been processed. A line
diff --git a/sequencer.h b/sequencer.h
index 4a051e5dc9..6a1a23541f 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -4,6 +4,7 @@
 const char *git_path_commit_editmsg(void);
 const char *git_path_seq_dir(void);
 const char *rebase_path_todo(void);
+const char *rebase_path_todo_backup(void);
 
 #define APPEND_SIGNOFF_DEDUP (1u << 0)
 

diff --git a/sequencer.c b/sequencer.c
index 0763eeae25..3069d4c6a2 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4351,7 +4351,7 @@ int transform_todo_file(unsigned flags)
 	int res;
 
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
+		return error_errno(_("could not read '%s'."), todo_file);
 
 	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);

diff --git a/sequencer.c b/sequencer.c
index a03505f582..0763eeae25 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4457,7 +4457,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	struct todo_list new_todo = TODO_LIST_INIT;
 	struct strbuf *buf = &todo_list->buf;
 	struct object_id oid;
-	int command_count;
+	int command_count, res;
 
 	get_oid(onto, &oid);
 	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
@@ -4484,24 +4484,16 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return error(_("nothing to do"));
 	}
 
-	if (todo_list_write_to_file(todo_list, todo_file,
-				    shortrevisions, shortonto, command_count,
-				    1, -1, flags | TODO_LIST_SHORTEN_IDS))
-		return error_errno(_("could not write '%s'"), todo_file);
-
-	if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
-		return error(_("could not copy '%s' to '%s'."), todo_file,
-			     rebase_path_todo_backup());
-
-	if (launch_sequence_editor(todo_file, &new_todo.buf, NULL)) {
+	res = edit_todo_list(todo_list, &new_todo, flags,
+			     command_count, shortrevisions, shortonto);
+	if (res == -1)
+		return -1;
+	else if (res == -2) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
 
 		return -1;
-	}
-
-	strbuf_stripspace(&new_todo.buf, 1);
-	if (new_todo.buf.len == 0) {
+	} else if (res == -3) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
 		todo_list_release(&new_todo);

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 0f83422aa0..28e6947ecb 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -34,6 +34,26 @@ static int edit_todo_file(unsigned flags)
 	return 0;
 }
 
+static int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	res = todo_list_write_to_file(&todo_list, todo_file,
+				      NULL, NULL, 0, 0, -1, flags);
+	todo_list_release(&todo_list);
+	return res;
+}
+
 static int get_revision_ranges(const char *upstream, const char *onto,
 			       const char **head_hash,
 			       char **revisions, char **shortrevisions)
diff --git a/sequencer.c b/sequencer.c
index 3069d4c6a2..a1b81bd544 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4344,26 +4344,6 @@ int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
 	return res;
 }
 
-int transform_todo_file(unsigned flags)
-{
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	int res;
-
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	res = todo_list_write_to_file(&todo_list, todo_file,
-				      NULL, NULL, 0, 0, -1, flags);
-	todo_list_release(&todo_list);
-	return res;
-}
-
 static const char edit_todo_list_advice[] =
 N_("You can fix this with 'git rebase --edit-todo' "
 "and then run 'git rebase --continue'.\n"
diff --git a/sequencer.h b/sequencer.h
index 6a1a23541f..d35ca61d5d 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -134,7 +134,6 @@ int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);
-int transform_todo_file(unsigned flags);
 int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,

diff --git a/sequencer.c b/sequencer.c
index 9e1ab3a2a7..07cc91d8db 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2066,6 +2066,8 @@ static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
 	char *p = buf, *next_p;
 	int i, res = 0, fixup_okay = file_exists(rebase_path_done());
 
+	todo_list->current = todo_list->nr = 0;
+
 	for (i = 1; *p; i++, p = next_p) {
 		char *eol = strchrnul(p, '\n');
 
@@ -2079,7 +2081,10 @@ static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
 		if (parse_insn_line(item, p, eol)) {
 			res = error(_("invalid line %d: %.*s"),
 				i, (int)(eol - p), p);
-			item->command = TODO_NOOP;
+			item->command = TODO_COMMENT + 1;
+			item->arg = p;
+			item->arg_len = (int)(eol - p);
+			item->commit = NULL;
 		}
 
 		if (fixup_okay)

builtin/rebase--interactive.c, rebase-interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index a2ab68ed06..abdf6126df 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -252,7 +252,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	}
 	case SHORTEN_OIDS:
 	case EXPAND_OIDS:
-		ret = transform_todos(flags);
+		ret = transform_todo_file(flags);
 		break;
 	case CHECK_TODO_LIST:
 		ret = check_todo_list();
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 78f3263fc1..4cd487a450 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -69,7 +69,7 @@ int edit_todo_list(unsigned flags)
 
 	strbuf_release(&buf);
 
-	transform_todos(flags | TODO_LIST_SHORTEN_IDS);
+	transform_todo_file(flags | TODO_LIST_SHORTEN_IDS);
 
 	if (strbuf_read_file(&buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
@@ -85,7 +85,7 @@ int edit_todo_list(unsigned flags)
 	if (launch_sequence_editor(todo_file, NULL, NULL))
 		return -1;
 
-	transform_todos(flags & ~(TODO_LIST_SHORTEN_IDS));
+	transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS));
 
 	return 0;
 }
diff --git a/sequencer.c b/sequencer.c
index 7adbeaa27d..e1097660ed 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4454,23 +4454,13 @@ int sequencer_add_exec_commands(const char *commands)
 	return i;
 }
 
-int transform_todos(unsigned flags)
+void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct todo_item *item;
 	int i;
 
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
+	for (item = todo_list->items, i = 0; i < todo_list->nr; i++, item++) {
 		/* if the item is not a command write it and continue */
 		if (item->command >= TODO_COMMENT) {
 			strbuf_addf(&buf, "%.*s\n", item->arg_len, item->arg);
@@ -4506,9 +4496,33 @@ int transform_todos(unsigned flags)
 			strbuf_addf(&buf, " %.*s\n", item->arg_len, item->arg);
 	}
 
-	i = write_message(buf.buf, buf.len, todo_file, 0);
+	strbuf_reset(&todo_list->buf);
+	strbuf_add(&todo_list->buf, buf.buf, buf.len);
+	strbuf_release(&buf);
+
+	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
+		BUG("unusable todo list");
+}
+
+int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_transform(&todo_list, flags);
+
+	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
 	todo_list_release(&todo_list);
-	return i;
+	return res;
 }
 
 enum missing_commit_check_level get_missing_commit_check_level(void)
@@ -4769,7 +4783,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return error(_("could not copy '%s' to '%s'."), todo_file,
 			     rebase_path_todo_backup());
 
-	if (transform_todos(flags | TODO_LIST_SHORTEN_IDS))
+	if (transform_todo_file(flags | TODO_LIST_SHORTEN_IDS))
 		return error(_("could not transform the todo list"));
 
 	strbuf_reset(buf);
@@ -4798,7 +4812,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return -1;
 	}
 
-	if (transform_todos(flags & ~(TODO_LIST_SHORTEN_IDS)))
+	if (transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS)))
 		return error(_("could not transform the todo list"));
 
 	if (opts->allow_ff && skip_unnecessary_picks(&oid))
diff --git a/sequencer.h b/sequencer.h
index 84f813305f..708d042f0e 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,7 @@ struct todo_list {
 #define TODO_LIST_INIT { STRBUF_INIT }
 
 int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
+void todo_list_transform(struct todo_list *todo_list, unsigned flags);
 void todo_list_release(struct todo_list *todo_list);
 
 /* Call this to setup defaults before parsing command line options */
@@ -142,7 +143,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(const char *command);
-int transform_todos(unsigned flags);
+int transform_todo_file(unsigned flags);
 enum missing_commit_check_level get_missing_commit_check_level(void);
 int check_todo_list(void);
 int complete_action(struct replay_opts *opts, unsigned flags,

sequencer.c, sequencer.h

diff --git a/sequencer.c b/sequencer.c
index e1097660ed..19f24825d4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4454,24 +4454,27 @@ int sequencer_add_exec_commands(const char *commands)
 	return i;
 }
 
-void todo_list_transform(struct todo_list *todo_list, unsigned flags)
+static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,
+				int num, unsigned flags)
 {
-	struct strbuf buf = STRBUF_INIT;
 	struct todo_item *item;
-	int i;
+	int i, max = todo_list->nr;
 
-	for (item = todo_list->items, i = 0; i < todo_list->nr; i++, item++) {
+	if (num > 0 && num < max)
+		max = num;
+
+	for (item = todo_list->items, i = 0; i < max; i++, item++) {
 		/* if the item is not a command write it and continue */
 		if (item->command >= TODO_COMMENT) {
-			strbuf_addf(&buf, "%.*s\n", item->arg_len, item->arg);
+			strbuf_addf(buf, "%.*s\n", item->arg_len, item->arg);
 			continue;
 		}
 
 		/* add command to the buffer */
 		if (flags & TODO_LIST_ABBREVIATE_CMDS)
-			strbuf_addch(&buf, command_to_char(item->command));
+			strbuf_addch(buf, command_to_char(item->command));
 		else
-			strbuf_addstr(&buf, command_to_string(item->command));
+			strbuf_addstr(buf, command_to_string(item->command));
 
 		/* add commit id */
 		if (item->commit) {
@@ -4481,27 +4484,47 @@ void todo_list_transform(struct todo_list *todo_list, unsigned flags)
 
 			if (item->command == TODO_MERGE) {
 				if (item->flags & TODO_EDIT_MERGE_MSG)
-					strbuf_addstr(&buf, " -c");
+					strbuf_addstr(buf, " -c");
 				else
-					strbuf_addstr(&buf, " -C");
+					strbuf_addstr(buf, " -C");
 			}
 
-			strbuf_addf(&buf, " %s", oid);
+			strbuf_addf(buf, " %s", oid);
 		}
 
 		/* add all the rest */
 		if (!item->arg_len)
-			strbuf_addch(&buf, '\n');
+			strbuf_addch(buf, '\n');
 		else
-			strbuf_addf(&buf, " %.*s\n", item->arg_len, item->arg);
+			strbuf_addf(buf, " %.*s\n", item->arg_len, item->arg);
 	}
+}
 
-	strbuf_reset(&todo_list->buf);
-	strbuf_add(&todo_list->buf, buf.buf, buf.len);
+int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
+			    const char *shortrevisions, const char *shortonto,
+			    int num, unsigned flags)
+{
+	int edit_todo = !(shortrevisions && shortonto), res;
+	struct strbuf buf = STRBUF_INIT;
+
+	todo_list_to_strbuf(todo_list, &buf, num, flags);
+
+	if (flags & TODO_LIST_APPEND_TODO_HELP) {
+		int command_count = count_commands(todo_list);
+		if (!edit_todo) {
+			strbuf_addch(&buf, '\n');
+			strbuf_commented_addf(&buf, Q_("Rebase %s onto %s (%d command)",
+						       "Rebase %s onto %s (%d commands)",
+						       command_count),
+					      shortrevisions, shortonto, command_count);
+		}
+		append_todo_help(edit_todo, flags & TODO_LIST_KEEP_EMPTY, &buf);
+	}
+
+	res = write_message(buf.buf, buf.len, file, 0);
 	strbuf_release(&buf);
 
-	if (todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list))
-		BUG("unusable todo list");
+	return res;
 }
 
 int transform_todo_file(unsigned flags)
@@ -4518,9 +4541,8 @@ int transform_todo_file(unsigned flags)
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
 
-	todo_list_transform(&todo_list, flags);
-
-	res = write_message(todo_list.buf.buf, todo_list.buf.len, todo_file, 0);
+	res = todo_list_write_to_file(&todo_list, todo_file,
+				      NULL, NULL, -1, flags);
 	todo_list_release(&todo_list);
 	return res;
 }
diff --git a/sequencer.h b/sequencer.h
index 708d042f0e..e69357c95b 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,7 +119,9 @@ struct todo_list {
 #define TODO_LIST_INIT { STRBUF_INIT }
 
 int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
-void todo_list_transform(struct todo_list *todo_list, unsigned flags);
+int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
+			    const char *shortrevisions, const char *shortonto,
+			    int num, unsigned flags);
 void todo_list_release(struct todo_list *todo_list);
 
 /* Call this to setup defaults before parsing command line options */
@@ -139,6 +141,8 @@ int sequencer_remove_state(struct replay_opts *opts);
  * commits should be rebased onto the new base, this flag needs to be passed.
  */
 #define TODO_LIST_REBASE_COUSINS (1U << 4)
+#define TODO_LIST_APPEND_TODO_HELP (1U << 5)
+
 int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 

builtin/rebase--interactive.c, rebase-interactive.c, rebase-interactive.h, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index abdf6126df..c1d87c0fe6 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -255,7 +255,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = transform_todo_file(flags);
 		break;
 	case CHECK_TODO_LIST:
-		ret = check_todo_list();
+		ret = check_todo_list_from_file();
 		break;
 	case REARRANGE_SQUASH:
 		ret = rearrange_squash();
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 4cd487a450..3adcf39e07 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -1,8 +1,32 @@
 #include "cache.h"
 #include "commit.h"
-#include "rebase-interactive.h"
 #include "sequencer.h"
+#include "rebase-interactive.h"
 #include "strbuf.h"
+#include "commit-slab.h"
+#include "config.h"
+
+enum missing_commit_check_level {
+	MISSING_COMMIT_CHECK_IGNORE = 0,
+	MISSING_COMMIT_CHECK_WARN,
+	MISSING_COMMIT_CHECK_ERROR
+};
+
+static enum missing_commit_check_level get_missing_commit_check_level(void)
+{
+	const char *value;
+
+	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
+			!strcasecmp("ignore", value))
+		return MISSING_COMMIT_CHECK_IGNORE;
+	if (!strcasecmp("warn", value))
+		return MISSING_COMMIT_CHECK_WARN;
+	if (!strcasecmp("error", value))
+		return MISSING_COMMIT_CHECK_ERROR;
+	warning(_("unrecognized setting %s for option "
+		  "rebase.missingCommitsCheck. Ignoring."), value);
+	return MISSING_COMMIT_CHECK_IGNORE;
+}
 
 void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 		      struct strbuf *buf)
@@ -89,3 +113,67 @@ int edit_todo_list(unsigned flags)
 
 	return 0;
 }
+
+define_commit_slab(commit_seen, unsigned char);
+/*
+ * Check if the user dropped some commits by mistake
+ * Behaviour determined by rebase.missingCommitsCheck.
+ * Check if there is an unrecognized command or a
+ * bad SHA-1 in a command.
+ */
+int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo)
+{
+	enum missing_commit_check_level check_level = get_missing_commit_check_level();
+	struct strbuf missing = STRBUF_INIT;
+	int res = 0, i;
+	struct commit_seen commit_seen;
+
+	init_commit_seen(&commit_seen);
+
+	if (check_level == MISSING_COMMIT_CHECK_IGNORE)
+		goto leave_check;
+
+	/* Mark the commits in git-rebase-todo as seen */
+	for (i = 0; i < new_todo->nr; i++) {
+		struct commit *commit = new_todo->items[i].commit;
+		if (commit)
+			*commit_seen_at(&commit_seen, commit) = 1;
+	}
+
+	/* Find commits in git-rebase-todo.backup yet unseen */
+	for (i = old_todo->nr - 1; i >= 0; i--) {
+		struct todo_item *item = old_todo->items + i;
+		struct commit *commit = item->commit;
+		if (commit && !*commit_seen_at(&commit_seen, commit)) {
+			strbuf_addf(&missing, " - %s %.*s\n",
+				    find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV),
+				    item->arg_len, item->arg);
+			*commit_seen_at(&commit_seen, commit) = 1;
+		}
+	}
+
+	/* Warn about missing commits */
+	if (!missing.len)
+		goto leave_check;
+
+	if (check_level == MISSING_COMMIT_CHECK_ERROR)
+		res = 1;
+
+	fprintf(stderr,
+		_("Warning: some commits may have been dropped accidentally.\n"
+		"Dropped commits (newer to older):\n"));
+
+	/* Make the list user-friendly and display */
+	fputs(missing.buf, stderr);
+	strbuf_release(&missing);
+
+	fprintf(stderr, _("To avoid this message, use \"drop\" to "
+		"explicitly remove a commit.\n\n"
+		"Use 'git config rebase.missingCommitsCheck' to change "
+		"the level of warnings.\n"
+		"The possible behaviours are: ignore, warn, error.\n\n"));
+
+leave_check:
+	clear_commit_seen(&commit_seen);
+	return res;
+}
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 971da03776..6bc7bc315d 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -4,5 +4,6 @@
 void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 		      struct strbuf *buf);
 int edit_todo_list(unsigned flags);
+int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index 19f24825d4..900899ef20 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4547,111 +4547,37 @@ int transform_todo_file(unsigned flags)
 	return res;
 }
 
-enum missing_commit_check_level get_missing_commit_check_level(void)
-{
-	const char *value;
-
-	if (git_config_get_value("rebase.missingcommitscheck", &value) ||
-			!strcasecmp("ignore", value))
-		return MISSING_COMMIT_CHECK_IGNORE;
-	if (!strcasecmp("warn", value))
-		return MISSING_COMMIT_CHECK_WARN;
-	if (!strcasecmp("error", value))
-		return MISSING_COMMIT_CHECK_ERROR;
-	warning(_("unrecognized setting %s for option "
-		  "rebase.missingCommitsCheck. Ignoring."), value);
-	return MISSING_COMMIT_CHECK_IGNORE;
-}
+static const char edit_todo_list_advice[] =
+N_("You can fix this with 'git rebase --edit-todo' "
+"and then run 'git rebase --continue'.\n"
+"Or you can abort the rebase with 'git rebase"
+" --abort'.\n");
 
-define_commit_slab(commit_seen, unsigned char);
-/*
- * Check if the user dropped some commits by mistake
- * Behaviour determined by rebase.missingCommitsCheck.
- * Check if there is an unrecognized command or a
- * bad SHA-1 in a command.
- */
-int check_todo_list(void)
+int check_todo_list_from_file(void)
 {
-	enum missing_commit_check_level check_level = get_missing_commit_check_level();
-	struct strbuf todo_file = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf missing = STRBUF_INIT;
-	int advise_to_edit_todo = 0, res = 0, i;
-	struct commit_seen commit_seen;
-
-	init_commit_seen(&commit_seen);
+	struct todo_list old_todo = TODO_LIST_INIT, new_todo = TODO_LIST_INIT;
+	int res = 0;
 
-	strbuf_addstr(&todo_file, rebase_path_todo());
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
+	if (strbuf_read_file_or_whine(&new_todo.buf, rebase_path_todo()) < 0) {
 		res = -1;
-		goto leave_check;
-	}
-	advise_to_edit_todo = res =
-		todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-
-	if (res || check_level == MISSING_COMMIT_CHECK_IGNORE)
-		goto leave_check;
-
-	/* Mark the commits in git-rebase-todo as seen */
-	for (i = 0; i < todo_list.nr; i++) {
-		struct commit *commit = todo_list.items[i].commit;
-		if (commit)
-			*commit_seen_at(&commit_seen, commit) = 1;
+		goto out;
 	}
 
-	todo_list_release(&todo_list);
-	strbuf_addstr(&todo_file, ".backup");
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
+	if (strbuf_read_file_or_whine(&old_todo.buf, rebase_path_todo_backup()) < 0) {
 		res = -1;
-		goto leave_check;
-	}
-	strbuf_release(&todo_file);
-	res = !!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-
-	/* Find commits in git-rebase-todo.backup yet unseen */
-	for (i = todo_list.nr - 1; i >= 0; i--) {
-		struct todo_item *item = todo_list.items + i;
-		struct commit *commit = item->commit;
-		if (commit && !*commit_seen_at(&commit_seen, commit)) {
-			strbuf_addf(&missing, " - %s %.*s\n",
-				    short_commit_name(commit),
-				    item->arg_len, item->arg);
-			*commit_seen_at(&commit_seen, commit) = 1;
-		}
+		goto out;
 	}
 
-	/* Warn about missing commits */
-	if (!missing.len)
-		goto leave_check;
-
-	if (check_level == MISSING_COMMIT_CHECK_ERROR)
-		advise_to_edit_todo = res = 1;
-
-	fprintf(stderr,
-		_("Warning: some commits may have been dropped accidentally.\n"
-		"Dropped commits (newer to older):\n"));
-
-	/* Make the list user-friendly and display */
-	fputs(missing.buf, stderr);
-	strbuf_release(&missing);
-
-	fprintf(stderr, _("To avoid this message, use \"drop\" to "
-		"explicitly remove a commit.\n\n"
-		"Use 'git config rebase.missingCommitsCheck' to change "
-		"the level of warnings.\n"
-		"The possible behaviours are: ignore, warn, error.\n\n"));
-
-leave_check:
-	clear_commit_seen(&commit_seen);
-	strbuf_release(&todo_file);
-	todo_list_release(&todo_list);
-
-	if (advise_to_edit_todo)
-		fprintf(stderr,
-			_("You can fix this with 'git rebase --edit-todo' "
-			  "and then run 'git rebase --continue'.\n"
-			  "Or you can abort the rebase with 'git rebase"
-			  " --abort'.\n"));
+	res = todo_list_parse_insn_buffer(old_todo.buf.buf, &old_todo);
+	if (!res)
+		res = todo_list_parse_insn_buffer(new_todo.buf.buf, &new_todo);
+	if (!res)
+		res = todo_list_check(&old_todo, &new_todo);
+	if (res)
+		fprintf(stderr, _(edit_todo_list_advice));
+out:
+	todo_list_release(&old_todo);
+	todo_list_release(&new_todo);
 
 	return res;
 }
@@ -4829,7 +4755,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_release(&todo_list);
 
-	if (check_todo_list()) {
+	if (check_todo_list_from_file()) {
 		checkout_onto(opts, onto_name, onto, orig_head);
 		return -1;
 	}
diff --git a/sequencer.h b/sequencer.h
index e69357c95b..c78f00aadd 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -63,12 +63,6 @@ struct replay_opts {
 };
 #define REPLAY_OPTS_INIT { .action = -1, .current_fixups = STRBUF_INIT }
 
-enum missing_commit_check_level {
-	MISSING_COMMIT_CHECK_IGNORE = 0,
-	MISSING_COMMIT_CHECK_WARN,
-	MISSING_COMMIT_CHECK_ERROR
-};
-
 int write_message(const void *buf, size_t len, const char *filename,
 		  int append_eol);
 
@@ -148,8 +142,7 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 int sequencer_add_exec_commands(const char *command);
 int transform_todo_file(unsigned flags);
-enum missing_commit_check_level get_missing_commit_check_level(void);
-int check_todo_list(void);
+int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, const char *cmd,

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index c1d87c0fe6..1fb5a43c0d 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -65,7 +65,7 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 				 const char *onto, const char *onto_name,
 				 const char *squash_onto, const char *head_name,
 				 const char *restrict_revision, char *raw_strategies,
-				 const char *cmd, unsigned autosquash)
+				 struct string_list *commands, unsigned autosquash)
 {
 	int ret;
 	const char *head_hash = NULL;
@@ -115,7 +115,7 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	else {
 		discard_cache();
 		ret = complete_action(opts, flags, shortrevisions, onto_name, onto,
-				      head_hash, cmd, autosquash);
+				      head_hash, commands, autosquash);
 	}
 
 	free(revisions);
@@ -138,6 +138,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	const char *onto = NULL, *onto_name = NULL, *restrict_revision = NULL,
 		*squash_onto = NULL, *upstream = NULL, *head_name = NULL,
 		*switch_to = NULL, *cmd = NULL;
+	struct string_list commands = STRING_LIST_INIT_DUP;
 	char *raw_strategies = NULL;
 	enum {
 		NONE = 0, CONTINUE, SKIP, EDIT_TODO, SHOW_CURRENT_PATCH,
@@ -220,6 +221,12 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		warning(_("--[no-]rebase-cousins has no effect without "
 			  "--rebase-merges"));
 
+	if (cmd && *cmd) {
+		string_list_split(&commands, cmd, '\n', -1);
+		if (strlen(commands.items[commands.nr - 1].string) == 0)
+			--commands.nr;
+	}
+
 	switch (command) {
 	case NONE:
 		if (!onto && !upstream)
@@ -227,7 +234,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 
 		ret = do_interactive_rebase(&opts, flags, switch_to, upstream, onto,
 					    onto_name, squash_onto, head_name, restrict_revision,
-					    raw_strategies, cmd, autosquash);
+					    raw_strategies, &commands, autosquash);
 		break;
 	case SKIP: {
 		struct string_list merge_rr = STRING_LIST_INIT_DUP;
@@ -261,7 +268,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = rearrange_squash();
 		break;
 	case ADD_EXEC:
-		ret = sequencer_add_exec_commands(cmd);
+		ret = sequencer_add_exec_commands(&commands);
 		break;
 	default:
 		BUG("invalid command '%d'", command);
diff --git a/sequencer.c b/sequencer.c
index 900899ef20..11692d0b98 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4394,24 +4394,29 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 	return 0;
 }
 
-/*
- * Add commands after pick and (series of) squash/fixup commands
- * in the todo list.
- */
-int sequencer_add_exec_commands(const char *commands)
+static void todo_list_add_exec_commands(struct todo_list *todo_list,
+					struct string_list *commands)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf *buf = &todo_list.buf;
-	size_t offset = 0, commands_len = strlen(commands);
-	int i, insert;
+	struct strbuf *buf = &todo_list->buf;
+	const char *old_buf = buf->buf;
+	size_t base_length = buf->len;
+	int i, insert, nr = 0, alloc = 0;
+	struct todo_item *items = NULL, *base_items = NULL;
 
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
+	for (i = 0; i < commands->nr; ++i) {
+		strbuf_addstr(buf, commands->items[i].string);
+		strbuf_addch(buf, '\n');
+	}
 
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
+	base_items = xcalloc(commands->nr, sizeof(struct todo_item));
+	for (i = 0; i < commands->nr; ++i) {
+		size_t command_len = strlen(commands->items[i].string) - strlen("exec ");
+
+		base_items[i].command = TODO_EXEC;
+		base_items[i].offset_in_buf = base_length + strlen("exec ");
+		base_items[i].arg = buf->buf + base_items[i].offset_in_buf;
+		base_items[i].arg_len = command_len;
+		base_length = base_items[i].offset_in_buf + base_items[i].arg_len + 1;
 	}
 
 	/*
@@ -4420,38 +4425,62 @@ int sequencer_add_exec_commands(const char *commands)
 	 * those chains if there are any.
 	 */
 	insert = -1;
-	for (i = 0; i < todo_list.nr; i++) {
-		enum todo_command command = todo_list.items[i].command;
-
-		if (insert >= 0) {
-			/* skip fixup/squash chains */
-			if (command == TODO_COMMENT)
-				continue;
-			else if (is_fixup(command)) {
-				insert = i + 1;
-				continue;
-			}
-			strbuf_insert(buf,
-				      todo_list.items[insert].offset_in_buf +
-				      offset, commands, commands_len);
-			offset += commands_len;
+	for (i = 0; i < todo_list->nr; i++) {
+		enum todo_command command = todo_list->items[i].command;
+		if (todo_list->items[i].arg)
+			todo_list->items[i].arg = todo_list->items[i].arg - old_buf + buf->buf;
+
+		if (insert >= 0 && command != TODO_COMMENT && !is_fixup(command)) {
+			ALLOC_GROW(items, nr + commands->nr, alloc);
+			COPY_ARRAY(items + nr, base_items, commands->nr);
+			nr += commands->nr;
 			insert = -1;
 		}
 
-		if (command == TODO_PICK || command == TODO_MERGE)
+		ALLOC_GROW(items, nr + 1, alloc);
+		items[nr++] = todo_list->items[i];
+
+		if (command == TODO_PICK || command == TODO_MERGE || is_fixup(command))
 			insert = i + 1;
 	}
 
 	/* insert or append final <commands> */
-	if (insert >= 0 && insert < todo_list.nr)
-		strbuf_insert(buf, todo_list.items[insert].offset_in_buf +
-			      offset, commands, commands_len);
-	else if (insert >= 0 || !offset)
-		strbuf_add(buf, commands, commands_len);
+	if (insert >= 0 || nr == todo_list->nr) {
+		ALLOC_GROW(items, nr + commands->nr, alloc);
+		COPY_ARRAY(items + nr, base_items, commands->nr);
+		nr += commands->nr;
+	}
+
+	free(base_items);
+	FREE_AND_NULL(todo_list->items);
+	todo_list->items = items;
+	todo_list->nr = nr;
+	todo_list->alloc = alloc;
+}
+
+/*
+ * Add commands after pick and (series of) squash/fixup commands
+ * in the todo list.
+ */
+int sequencer_add_exec_commands(struct string_list *commands)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
 
-	i = write_message(buf->buf, buf->len, todo_file, 0);
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_add_exec_commands(&todo_list, commands);
+	res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, -1, 0);
 	todo_list_release(&todo_list);
-	return i;
+
+	return res;
 }
 
 static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,
@@ -4677,7 +4706,7 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
-		    const char *onto, const char *orig_head, const char *cmd,
+		    const char *onto, const char *orig_head, struct string_list *commands,
 		    unsigned autosquash)
 {
 	const char *shortonto, *todo_file = rebase_path_todo();
@@ -4696,8 +4725,8 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	if (autosquash && rearrange_squash())
 		return -1;
 
-	if (cmd && *cmd)
-		sequencer_add_exec_commands(cmd);
+	if (commands->nr)
+		sequencer_add_exec_commands(commands);
 
 	if (strbuf_read_file(buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
diff --git a/sequencer.h b/sequencer.h
index c78f00aadd..d7b52044bd 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -140,12 +140,12 @@ int sequencer_remove_state(struct replay_opts *opts);
 int sequencer_make_script(FILE *out, int argc, const char **argv,
 			  unsigned flags);
 
-int sequencer_add_exec_commands(const char *command);
+int sequencer_add_exec_commands(struct string_list *commands);
 int transform_todo_file(unsigned flags);
 int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
-		    const char *onto, const char *orig_head, const char *cmd,
+		    const char *onto, const char *orig_head, struct string_list *commands,
 		    unsigned autosquash);
 int rearrange_squash(void);
 

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 1fb5a43c0d..a6d83a684e 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -265,7 +265,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		ret = check_todo_list_from_file();
 		break;
 	case REARRANGE_SQUASH:
-		ret = rearrange_squash();
+		ret = rearrange_squash_in_todo_file();
 		break;
 	case ADD_EXEC:
 		ret = sequencer_add_exec_commands(&commands);
diff --git a/sequencer.c b/sequencer.c
index 11692d0b98..fce97e5f11 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4722,7 +4722,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	    write_message("noop\n", 5, todo_file, 0))
 		return -1;
 
-	if (autosquash && rearrange_squash())
+	if (autosquash && rearrange_squash_in_todo_file())
 		return -1;
 
 	if (commands->nr)
@@ -4828,21 +4828,13 @@ define_commit_slab(commit_todo_item, struct todo_item *);
  * message will have to be retrieved from the commit (as the oneline in the
  * script cannot be trusted) in order to normalize the autosquash arrangement.
  */
-int rearrange_squash(void)
+static int todo_list_rearrange_squash(struct todo_list *todo_list)
 {
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct hashmap subject2item;
-	int res = 0, rearranged = 0, *next, *tail, i;
+	int rearranged = 0, *next, *tail, i, nr = 0, alloc = 0;
 	char **subjects;
 	struct commit_todo_item commit_todo;
-
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	struct todo_item *items = NULL;
 
 	init_commit_todo_item(&commit_todo);
 	/*
@@ -4855,13 +4847,13 @@ int rearrange_squash(void)
 	 * be moved to appear after the i'th.
 	 */
 	hashmap_init(&subject2item, (hashmap_cmp_fn) subject2item_cmp,
-		     NULL, todo_list.nr);
-	ALLOC_ARRAY(next, todo_list.nr);
-	ALLOC_ARRAY(tail, todo_list.nr);
-	ALLOC_ARRAY(subjects, todo_list.nr);
-	for (i = 0; i < todo_list.nr; i++) {
+		     NULL, todo_list->nr);
+	ALLOC_ARRAY(next, todo_list->nr);
+	ALLOC_ARRAY(tail, todo_list->nr);
+	ALLOC_ARRAY(subjects, todo_list->nr);
+	for (i = 0; i < todo_list->nr; i++) {
 		struct strbuf buf = STRBUF_INIT;
-		struct todo_item *item = todo_list.items + i;
+		struct todo_item *item = todo_list->items + i;
 		const char *commit_buffer, *subject, *p;
 		size_t subject_len;
 		int i2 = -1;
@@ -4874,7 +4866,6 @@ int rearrange_squash(void)
 		}
 
 		if (is_fixup(item->command)) {
-			todo_list_release(&todo_list);
 			clear_commit_todo_item(&commit_todo);
 			return error(_("the script was already rearranged."));
 		}
@@ -4909,7 +4900,7 @@ int rearrange_squash(void)
 				 *commit_todo_item_at(&commit_todo, commit2))
 				/* found by commit name */
 				i2 = *commit_todo_item_at(&commit_todo, commit2)
-					- todo_list.items;
+					- todo_list->items;
 			else {
 				/* copy can be a prefix of the commit subject */
 				for (i2 = 0; i2 < i; i2++)
@@ -4922,7 +4913,7 @@ int rearrange_squash(void)
 		}
 		if (i2 >= 0) {
 			rearranged = 1;
-			todo_list.items[i].command =
+			todo_list->items[i].command =
 				starts_with(subject, "fixup!") ?
 				TODO_FIXUP : TODO_SQUASH;
 			if (next[i2] < 0)
@@ -4940,10 +4931,8 @@ int rearrange_squash(void)
 	}
 
 	if (rearranged) {
-		struct strbuf buf = STRBUF_INIT;
-
-		for (i = 0; i < todo_list.nr; i++) {
-			enum todo_command command = todo_list.items[i].command;
+		for (i = 0; i < todo_list->nr; i++) {
+			enum todo_command command = todo_list->items[i].command;
 			int cur = i;
 
 			/*
@@ -4954,37 +4943,47 @@ int rearrange_squash(void)
 				continue;
 
 			while (cur >= 0) {
-				const char *bol =
-					get_item_line(&todo_list, cur);
-				const char *eol =
-					get_item_line(&todo_list, cur + 1);
-
-				/* replace 'pick', by 'fixup' or 'squash' */
-				command = todo_list.items[cur].command;
-				if (is_fixup(command)) {
-					strbuf_addstr(&buf,
-						todo_command_info[command].str);
-					bol += strcspn(bol, " \t");
-				}
-
-				strbuf_add(&buf, bol, eol - bol);
-
+				ALLOC_GROW(items, nr + 1, alloc);
+				items[nr++] = todo_list->items[cur];
 				cur = next[cur];
 			}
 		}
 
-		res = rewrite_file(todo_file, buf.buf, buf.len);
-		strbuf_release(&buf);
+		FREE_AND_NULL(todo_list->items);
+		todo_list->items = items;
+		todo_list->nr = nr;
+		todo_list->alloc = alloc;
 	}
 
 	free(next);
 	free(tail);
-	for (i = 0; i < todo_list.nr; i++)
+	for (i = 0; i < todo_list->nr; i++)
 		free(subjects[i]);
 	free(subjects);
 	hashmap_free(&subject2item, 1);
-	todo_list_release(&todo_list);
 
 	clear_commit_todo_item(&commit_todo);
+
+	return 0;
+}
+
+int rearrange_squash_in_todo_file(void)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
+		return -1;
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+		todo_list_release(&todo_list);
+		return -1;
+	}
+
+	res = todo_list_rearrange_squash(&todo_list);
+	if (!res)
+		res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, -1, 0);
+
+	todo_list_release(&todo_list);
 	return res;
 }
diff --git a/sequencer.h b/sequencer.h
index d7b52044bd..1cd9d7f1e2 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -147,7 +147,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, struct string_list *commands,
 		    unsigned autosquash);
-int rearrange_squash(void);
+int rearrange_squash_in_todo_file(void);
 
 extern const char sign_off_header[];
 

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index a6d83a684e..c740a7dd5d 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -71,7 +71,8 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	const char *head_hash = NULL;
 	char *revisions = NULL, *shortrevisions = NULL;
 	struct argv_array make_script_args = ARGV_ARRAY_INIT;
-	FILE *todo_list;
+	FILE *todo_list_file;
+	struct todo_list todo_list = TODO_LIST_INIT;
 
 	if (prepare_branch_to_be_rebased(opts, switch_to))
 		return -1;
@@ -93,8 +94,8 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (!upstream && squash_onto)
 		write_file(path_squash_onto(), "%s\n", squash_onto);
 
-	todo_list = fopen(rebase_path_todo(), "w");
-	if (!todo_list) {
+	todo_list_file = fopen(rebase_path_todo(), "w");
+	if (!todo_list_file) {
 		free(revisions);
 		free(shortrevisions);
 
@@ -105,10 +106,11 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (restrict_revision)
 		argv_array_push(&make_script_args, restrict_revision);
 
-	ret = sequencer_make_script(todo_list,
+	ret = sequencer_make_script(&todo_list.buf,
 				    make_script_args.argc, make_script_args.argv,
 				    flags);
-	fclose(todo_list);
+	fputs(todo_list.buf.buf, todo_list_file);
+	fclose(todo_list_file);
 
 	if (ret)
 		error(_("could not generate todo list"));
@@ -120,6 +122,7 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 
 	free(revisions);
 	free(shortrevisions);
+	todo_list_release(&todo_list);
 	argv_array_clear(&make_script_args);
 
 	return ret;
diff --git a/sequencer.c b/sequencer.c
index fce97e5f11..3389a753b6 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4109,7 +4109,7 @@ static const char *label_oid(struct object_id *oid, const char *label,
 }
 
 static int make_script_with_merges(struct pretty_print_context *pp,
-				   struct rev_info *revs, FILE *out,
+				   struct rev_info *revs, struct strbuf *out,
 				   unsigned flags)
 {
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
@@ -4254,7 +4254,7 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	 * gathering commits not yet shown, reversing the list on the fly,
 	 * then outputting that list (labeling revisions as needed).
 	 */
-	fprintf(out, "%s onto\n", cmd_label);
+	strbuf_addf(out, "%s onto\n", cmd_label);
 	for (iter = tips; iter; iter = iter->next) {
 		struct commit_list *list = NULL, *iter2;
 
@@ -4264,9 +4264,9 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		entry = oidmap_get(&state.commit2label, &commit->object.oid);
 
 		if (entry)
-			fprintf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
+			strbuf_addf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
 		else
-			fprintf(out, "\n");
+			strbuf_addch(out, '\n');
 
 		while (oidset_contains(&interesting, &commit->object.oid) &&
 		       !oidset_contains(&shown, &commit->object.oid)) {
@@ -4279,8 +4279,8 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 		}
 
 		if (!commit)
-			fprintf(out, "%s %s\n", cmd_reset,
-				rebase_cousins ? "onto" : "[new root]");
+			strbuf_addf(out, "%s %s\n", cmd_reset,
+				    rebase_cousins ? "onto" : "[new root]");
 		else {
 			const char *to = NULL;
 
@@ -4293,12 +4293,12 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 					       &state);
 
 			if (!to || !strcmp(to, "onto"))
-				fprintf(out, "%s onto\n", cmd_reset);
+				strbuf_addf(out, "%s onto\n", cmd_reset);
 			else {
 				strbuf_reset(&oneline);
 				pretty_print_commit(pp, commit, &oneline);
-				fprintf(out, "%s %s # %s\n",
-					cmd_reset, to, oneline.buf);
+				strbuf_addf(out, "%s %s # %s\n",
+					    cmd_reset, to, oneline.buf);
 			}
 		}
 
@@ -4307,11 +4307,11 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 			entry = oidmap_get(&commit2todo, oid);
 			/* only show if not already upstream */
 			if (entry)
-				fprintf(out, "%s\n", entry->string);
+				strbuf_addf(out, "%s\n", entry->string);
 			entry = oidmap_get(&state.commit2label, oid);
 			if (entry)
-				fprintf(out, "%s %s\n",
-					cmd_label, entry->string);
+				strbuf_addf(out, "%s %s\n",
+					    cmd_label, entry->string);
 			oidset_insert(&shown, oid);
 		}
 
@@ -4333,12 +4333,11 @@ static int make_script_with_merges(struct pretty_print_context *pp,
 	return 0;
 }
 
-int sequencer_make_script(FILE *out, int argc, const char **argv,
+int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags)
 {
 	char *format = NULL;
 	struct pretty_print_context pp = {0};
-	struct strbuf buf = STRBUF_INIT;
 	struct rev_info revs;
 	struct commit *commit;
 	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
@@ -4381,16 +4380,13 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
 
 		if (!is_empty && (commit->object.flags & PATCHSAME))
 			continue;
-		strbuf_reset(&buf);
 		if (!keep_empty && is_empty)
-			strbuf_addf(&buf, "%c ", comment_line_char);
-		strbuf_addf(&buf, "%s %s ", insn,
+			strbuf_addf(out, "%c ", comment_line_char);
+		strbuf_addf(out, "%s %s ", insn,
 			    oid_to_hex(&commit->object.oid));
-		pretty_print_commit(&pp, commit, &buf);
-		strbuf_addch(&buf, '\n');
-		fputs(buf.buf, out);
+		pretty_print_commit(&pp, commit, out);
+		strbuf_addch(out, '\n');
 	}
-	strbuf_release(&buf);
 	return 0;
 }
 
diff --git a/sequencer.h b/sequencer.h
index 1cd9d7f1e2..fcde6e739d 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -137,7 +137,7 @@ int sequencer_remove_state(struct replay_opts *opts);
 #define TODO_LIST_REBASE_COUSINS (1U << 4)
 #define TODO_LIST_APPEND_TODO_HELP (1U << 5)
 
-int sequencer_make_script(FILE *out, int argc, const char **argv,
+int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(struct string_list *commands);

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index c740a7dd5d..99cbd1e8e3 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -71,7 +71,6 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	const char *head_hash = NULL;
 	char *revisions = NULL, *shortrevisions = NULL;
 	struct argv_array make_script_args = ARGV_ARRAY_INIT;
-	FILE *todo_list_file;
 	struct todo_list todo_list = TODO_LIST_INIT;
 
 	if (prepare_branch_to_be_rebased(opts, switch_to))
@@ -94,14 +93,6 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	if (!upstream && squash_onto)
 		write_file(path_squash_onto(), "%s\n", squash_onto);
 
-	todo_list_file = fopen(rebase_path_todo(), "w");
-	if (!todo_list_file) {
-		free(revisions);
-		free(shortrevisions);
-
-		return error_errno(_("could not open %s"), rebase_path_todo());
-	}
-
 	argv_array_pushl(&make_script_args, "", revisions, NULL);
 	if (restrict_revision)
 		argv_array_push(&make_script_args, restrict_revision);
@@ -109,15 +100,16 @@ static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 	ret = sequencer_make_script(&todo_list.buf,
 				    make_script_args.argc, make_script_args.argv,
 				    flags);
-	fputs(todo_list.buf.buf, todo_list_file);
-	fclose(todo_list_file);
 
 	if (ret)
 		error(_("could not generate todo list"));
 	else {
 		discard_cache();
+		if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
+			BUG("unusable todo list");
+
 		ret = complete_action(opts, flags, shortrevisions, onto_name, onto,
-				      head_hash, commands, autosquash);
+				      head_hash, commands, autosquash, &todo_list);
 	}
 
 	free(revisions);
diff --git a/sequencer.c b/sequencer.c
index 3389a753b6..64a99ab84f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4700,93 +4700,83 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 	return 0;
 }
 
+static int todo_list_rearrange_squash(struct todo_list *todo_list);
+
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, struct string_list *commands,
-		    unsigned autosquash)
+		    unsigned autosquash, struct todo_list *todo_list)
 {
 	const char *shortonto, *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	struct strbuf *buf = &(todo_list.buf);
+	struct todo_list new_todo = TODO_LIST_INIT;
+	struct strbuf *buf = &todo_list->buf;
 	struct object_id oid;
-	struct stat st;
 
 	get_oid(onto, &oid);
 	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
 
-	if (!lstat(todo_file, &st) && st.st_size == 0 &&
-	    write_message("noop\n", 5, todo_file, 0))
-		return -1;
+	if (buf->len == 0) {
+		struct todo_item *item = append_new_todo(todo_list);
+		item->command = TODO_NOOP;
+		item->commit = NULL;
+		item->arg = NULL;
+		item->arg_len = item->flags = item->offset_in_buf = 0;
+	}
 
-	if (autosquash && rearrange_squash_in_todo_file())
+	if (autosquash && todo_list_rearrange_squash(todo_list))
 		return -1;
 
 	if (commands->nr)
-		sequencer_add_exec_commands(commands);
-
-	if (strbuf_read_file(buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(buf->buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
+		todo_list_add_exec_commands(todo_list, commands);
 
-	if (count_commands(&todo_list) == 0) {
+	if (count_commands(todo_list) == 0) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
 
 		return error(_("nothing to do"));
 	}
 
-	strbuf_addch(buf, '\n');
-	strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
-				      "Rebase %s onto %s (%d commands)",
-				      count_commands(&todo_list)),
-			      shortrevisions, shortonto, count_commands(&todo_list));
-	append_todo_help(0, flags & TODO_LIST_KEEP_EMPTY, buf);
-
-	if (write_message(buf->buf, buf->len, todo_file, 0)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (todo_list_write_to_file(todo_list, todo_file,
+				    shortrevisions, shortonto, -1,
+				    flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP))
+		return error_errno(_("could not write '%s'"), todo_file);
 
 	if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
 		return error(_("could not copy '%s' to '%s'."), todo_file,
 			     rebase_path_todo_backup());
 
-	if (transform_todo_file(flags | TODO_LIST_SHORTEN_IDS))
-		return error(_("could not transform the todo list"));
-
-	strbuf_reset(buf);
-
-	if (launch_sequence_editor(todo_file, buf, NULL)) {
+	if (launch_sequence_editor(todo_file, &new_todo.buf, NULL)) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
 
 		return -1;
 	}
 
-	strbuf_stripspace(buf, 1);
-	if (buf->len == 0) {
+	strbuf_stripspace(&new_todo.buf, 1);
+	if (new_todo.buf.len == 0) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
-		todo_list_release(&todo_list);
+		todo_list_release(&new_todo);
 
 		return error(_("nothing to do"));
 	}
 
-	todo_list_release(&todo_list);
-
-	if (check_todo_list_from_file()) {
+	if (todo_list_parse_insn_buffer(new_todo.buf.buf, &new_todo) ||
+	    todo_list_check(todo_list, &new_todo)) {
+		fprintf(stderr, _(edit_todo_list_advice));
 		checkout_onto(opts, onto_name, onto, orig_head);
+		todo_list_release(&new_todo);
+
 		return -1;
 	}
 
-	if (transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS)))
-		return error(_("could not transform the todo list"));
+	if (todo_list_write_to_file(&new_todo, todo_file, NULL, NULL, -1,
+				    flags & ~(TODO_LIST_SHORTEN_IDS))) {
+		todo_list_release(&new_todo);
+		return error_errno(_("could not write '%s'"), todo_file);
+	}
+
+	todo_list_release(&new_todo);
 
 	if (opts->allow_ff && skip_unnecessary_picks(&oid))
 		return error(_("could not skip unnecessary pick commands"));
diff --git a/sequencer.h b/sequencer.h
index fcde6e739d..996e8ea2a6 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -146,7 +146,7 @@ int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    const char *onto, const char *orig_head, struct string_list *commands,
-		    unsigned autosquash);
+		    unsigned autosquash, struct todo_list *todo_list);
 int rearrange_squash_in_todo_file(void);
 
 extern const char sign_off_header[];

rebase-interactive.c, rebase-interactive.h, sequencer.c

diff --git a/rebase-interactive.c b/rebase-interactive.c
index 23569cfa3c..3b7b5e3382 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -28,7 +28,8 @@ static enum missing_commit_check_level get_missing_commit_check_level(void)
 	return MISSING_COMMIT_CHECK_IGNORE;
 }
 
-void append_todo_help(unsigned edit_todo, unsigned keep_empty,
+void append_todo_help(unsigned keep_empty, int command_count,
+		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf)
 {
 	const char *msg = _("\nCommands:\n"
@@ -48,6 +49,15 @@ void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 ".       specified). Use -c <commit> to reword the commit message.\n"
 "\n"
 "These lines can be re-ordered; they are executed from top to bottom.\n");
+	unsigned edit_todo = !(shortrevisions && shortonto);
+
+	if (!edit_todo) {
+		strbuf_addch(buf, '\n');
+		strbuf_commented_addf(buf, Q_("Rebase %s onto %s (%d command)",
+					      "Rebase %s onto %s (%d commands)",
+					      command_count),
+				      shortrevisions, shortonto, command_count);
+	}
 
 	strbuf_add_commented_lines(buf, msg, strlen(msg));
 
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 6bc7bc315d..61858f3a02 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -1,7 +1,8 @@
 #ifndef REBASE_INTERACTIVE_H
 #define REBASE_INTERACTIVE_H
 
-void append_todo_help(unsigned edit_todo, unsigned keep_empty,
+void append_todo_help(unsigned keep_empty, int command_count,
+		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
 int edit_todo_list(unsigned flags);
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
diff --git a/sequencer.c b/sequencer.c
index 1c405763c3..cf6f69c93e 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4529,22 +4529,13 @@ int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
 			    const char *shortrevisions, const char *shortonto,
 			    int num, unsigned flags)
 {
-	int edit_todo = !(shortrevisions && shortonto), res;
+	int res;
 	struct strbuf buf = STRBUF_INIT;
 
 	todo_list_to_strbuf(todo_list, &buf, num, flags);
-
-	if (flags & TODO_LIST_APPEND_TODO_HELP) {
-		int command_count = count_commands(todo_list);
-		if (!edit_todo) {
-			strbuf_addch(&buf, '\n');
-			strbuf_commented_addf(&buf, Q_("Rebase %s onto %s (%d command)",
-						       "Rebase %s onto %s (%d commands)",
-						       command_count),
-					      shortrevisions, shortonto, command_count);
-		}
-		append_todo_help(edit_todo, flags & TODO_LIST_KEEP_EMPTY, &buf);
-	}
+	if (flags & TODO_LIST_APPEND_TODO_HELP)
+		append_todo_help(flags & TODO_LIST_KEEP_EMPTY, count_commands(todo_list),
+				 shortrevisions, shortonto, &buf);
 
 	res = write_message(buf.buf, buf.len, file, 0);
 	strbuf_release(&buf);

diff --git a/rebase-interactive.c b/rebase-interactive.c
index 3adcf39e07..23569cfa3c 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -79,39 +79,33 @@ void append_todo_help(unsigned edit_todo, unsigned keep_empty,
 
 int edit_todo_list(unsigned flags)
 {
-	struct strbuf buf = STRBUF_INIT;
 	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
 
-	if (strbuf_read_file(&buf, todo_file, 0) < 0)
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
 
-	strbuf_stripspace(&buf, 1);
-	if (write_message(buf.buf, buf.len, todo_file, 0)) {
-		strbuf_release(&buf);
+	strbuf_stripspace(&todo_list.buf, 1);
+	todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
+	if (todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, -1,
+				    flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP)) {
+		todo_list_release(&todo_list);
 		return -1;
 	}
 
-	strbuf_release(&buf);
-
-	transform_todo_file(flags | TODO_LIST_SHORTEN_IDS);
-
-	if (strbuf_read_file(&buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	append_todo_help(1, 0, &buf);
-	if (write_message(buf.buf, buf.len, todo_file, 0)) {
-		strbuf_release(&buf);
+	strbuf_reset(&todo_list.buf);
+	if (launch_sequence_editor(todo_file, &todo_list.buf, NULL)) {
+		todo_list_release(&todo_list);
 		return -1;
 	}
 
-	strbuf_release(&buf);
+	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
+		res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, -1,
+					      flags & ~(TODO_LIST_SHORTEN_IDS));
 
-	if (launch_sequence_editor(todo_file, NULL, NULL))
-		return -1;
-
-	transform_todo_file(flags & ~(TODO_LIST_SHORTEN_IDS));
-
-	return 0;
+	todo_list_release(&todo_list);
+	return res;
 }
 
 define_commit_slab(commit_seen, unsigned char);

diff --git a/sequencer.c b/sequencer.c
index f04b002e37..02afd2f5cd 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4654,6 +4654,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	struct todo_list new_todo = TODO_LIST_INIT;
 	struct strbuf *buf = &todo_list->buf;
 	struct object_id oid;
+	int res;
 
 	get_oid(onto, &oid);
 	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
@@ -4679,24 +4680,15 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return error(_("nothing to do"));
 	}
 
-	if (todo_list_write_to_file(todo_list, todo_file,
-				    shortrevisions, shortonto, -1,
-				    flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP))
-		return error_errno(_("could not write '%s'"), todo_file);
-
-	if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
-		return error(_("could not copy '%s' to '%s'."), todo_file,
-			     rebase_path_todo_backup());
-
-	if (launch_sequence_editor(todo_file, &new_todo.buf, NULL)) {
+	res = edit_todo_list(todo_list, &new_todo, shortrevisions, shortonto, flags);
+	if (res == -1)
+		return -1;
+	else if (res == -2) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
 
 		return -1;
-	}
-
-	strbuf_stripspace(&new_todo.buf, 1);
-	if (new_todo.buf.len == 0) {
+	} else if (res == -3) {
 		apply_autostash(opts);
 		sequencer_remove_state(opts);
 		todo_list_release(&new_todo);

builtin/rebase--interactive.c, rebase-interactive.c, rebase-interactive.h, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 99cbd1e8e3..6871990544 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -13,6 +13,27 @@ static GIT_PATH_FUNC(path_state_dir, "rebase-merge/")
 static GIT_PATH_FUNC(path_squash_onto, "rebase-merge/squash-onto")
 static GIT_PATH_FUNC(path_interactive, "rebase-merge/interactive")
 
+static int edit_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT,
+		new_todo = TODO_LIST_INIT;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	strbuf_stripspace(&todo_list.buf, 1);
+	if (!edit_todo_list(&todo_list, &new_todo, NULL, NULL, flags) &&
+	    todo_list_write_to_file(&new_todo, todo_file, NULL, NULL, -1,
+				    flags & ~(TODO_LIST_SHORTEN_IDS)) < 0)
+		return error_errno(_("could not write '%s'"), todo_file);
+
+	todo_list_release(&todo_list);
+	todo_list_release(&new_todo);
+
+	return 0;
+}
+
 static int get_revision_ranges(const char *upstream, const char *onto,
 			       const char **head_hash,
 			       char **revisions, char **shortrevisions)
@@ -241,7 +262,7 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		break;
 	}
 	case EDIT_TODO:
-		ret = edit_todo_list(flags);
+		ret = edit_todo_file(flags);
 		break;
 	case SHOW_CURRENT_PATCH: {
 		struct child_process cmd = CHILD_PROCESS_INIT;
diff --git a/rebase-interactive.c b/rebase-interactive.c
index 3b7b5e3382..e0fa88b90e 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -87,35 +87,37 @@ void append_todo_help(unsigned keep_empty, int command_count,
 	}
 }
 
-int edit_todo_list(unsigned flags)
+int edit_todo_list(struct todo_list *todo_list, struct todo_list *new_todo,
+		   const char *shortrevisions, const char *shortonto,
+		   unsigned flags)
 {
 	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	int res = 0;
-
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error_errno(_("could not read '%s'."), todo_file);
-
-	strbuf_stripspace(&todo_list.buf, 1);
-	todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
-	if (todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, -1,
-				    flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP)) {
-		todo_list_release(&todo_list);
-		return -1;
+	unsigned initial = shortrevisions && shortonto;
+
+	if (initial) {
+		todo_list_write_to_file(todo_list, todo_file, shortrevisions, shortonto, -1,
+					flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP);
+
+		if (copy_file(rebase_path_todo_backup(), todo_file, 0666))
+			return error(_("could not copy '%s' to '%s'."), todo_file,
+				     rebase_path_todo_backup());
+	} else {
+		todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list);
+		todo_list_write_to_file(todo_list, todo_file, NULL, NULL, -1,
+					flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP);
 	}
 
-	strbuf_reset(&todo_list.buf);
-	if (launch_sequence_editor(todo_file, &todo_list.buf, NULL)) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	if (launch_sequence_editor(todo_file, &new_todo->buf, NULL))
+		return -2;
 
-	if (!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list))
-		res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, -1,
-					      flags & ~(TODO_LIST_SHORTEN_IDS));
+	strbuf_stripspace(&new_todo->buf, 1);
+	if (initial && new_todo->buf.len == 0)
+		return -3;
 
-	todo_list_release(&todo_list);
-	return res;
+	if (!initial)
+		todo_list_parse_insn_buffer(new_todo->buf.buf, new_todo);
+
+	return 0;
 }
 
 define_commit_slab(commit_seen, unsigned char);
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 61858f3a02..8d5c04521e 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -4,7 +4,9 @@
 void append_todo_help(unsigned keep_empty, int command_count,
 		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
-int edit_todo_list(unsigned flags);
+int edit_todo_list(struct todo_list *todo_list, struct todo_list *new_todo,
+		   const char *shortrevisions, const char *shortonto,
+		   unsigned flags);
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index cf6f69c93e..f04b002e37 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -55,8 +55,7 @@ static GIT_PATH_FUNC(rebase_path, "rebase-merge")
  * file and written to the tail of 'done'.
  */
 GIT_PATH_FUNC(rebase_path_todo, "rebase-merge/git-rebase-todo")
-static GIT_PATH_FUNC(rebase_path_todo_backup,
-		     "rebase-merge/git-rebase-todo.backup")
+GIT_PATH_FUNC(rebase_path_todo_backup, "rebase-merge/git-rebase-todo.backup")
 
 /*
  * The rebase command lines that have already been processed. A line
diff --git a/sequencer.h b/sequencer.h
index 996e8ea2a6..f6751d53b9 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -9,6 +9,7 @@ struct commit;
 const char *git_path_commit_editmsg(void);
 const char *git_path_seq_dir(void);
 const char *rebase_path_todo(void);
+const char *rebase_path_todo_backup(void);
 
 #define APPEND_SIGNOFF_DEDUP (1u << 0)
 

diff --git a/sequencer.c b/sequencer.c
index 02afd2f5cd..a55df3526f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4464,7 +4464,7 @@ int sequencer_add_exec_commands(struct string_list *commands)
 	int res;
 
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
+		return error_errno(_("could not read '%s'."), todo_file);
 
 	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);

builtin/rebase--interactive.c, sequencer.c, sequencer.h

diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 6871990544..580c6a3822 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -34,6 +34,26 @@ static int edit_todo_file(unsigned flags)
 	return 0;
 }
 
+static int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	res = todo_list_write_to_file(&todo_list, todo_file,
+				      NULL, NULL, -1, flags);
+	todo_list_release(&todo_list);
+	return res;
+}
+
 static int get_revision_ranges(const char *upstream, const char *onto,
 			       const char **head_hash,
 			       char **revisions, char **shortrevisions)
diff --git a/sequencer.c b/sequencer.c
index a55df3526f..896dd04150 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4542,26 +4542,6 @@ int todo_list_write_to_file(struct todo_list *todo_list, const char *file,
 	return res;
 }
 
-int transform_todo_file(unsigned flags)
-{
-	const char *todo_file = rebase_path_todo();
-	struct todo_list todo_list = TODO_LIST_INIT;
-	int res;
-
-	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
-		return error(_("could not read '%s'."), todo_file);
-
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
-		todo_list_release(&todo_list);
-		return error(_("unusable todo list: '%s'"), todo_file);
-	}
-
-	res = todo_list_write_to_file(&todo_list, todo_file,
-				      NULL, NULL, -1, flags);
-	todo_list_release(&todo_list);
-	return res;
-}
-
 static const char edit_todo_list_advice[] =
 N_("You can fix this with 'git rebase --edit-todo' "
 "and then run 'git rebase --continue'.\n"
diff --git a/sequencer.h b/sequencer.h
index f6751d53b9..ee59233344 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -142,7 +142,6 @@ int sequencer_make_script(struct strbuf *out, int argc, const char **argv,
 			  unsigned flags);
 
 int sequencer_add_exec_commands(struct string_list *commands);
-int transform_todo_file(unsigned flags);
 int check_todo_list_from_file(void);
 int complete_action(struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,

diff --git a/sequencer.c b/sequencer.c
index 64a99ab84f..1c405763c3 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4607,52 +4607,21 @@ int check_todo_list_from_file(void)
 	return res;
 }
 
-static int rewrite_file(const char *path, const char *buf, size_t len)
-{
-	int rc = 0;
-	int fd = open(path, O_WRONLY | O_TRUNC);
-	if (fd < 0)
-		return error_errno(_("could not open '%s' for writing"), path);
-	if (write_in_full(fd, buf, len) < 0)
-		rc = error_errno(_("could not write to '%s'"), path);
-	if (close(fd) && !rc)
-		rc = error_errno(_("could not close '%s'"), path);
-	return rc;
-}
-
 /* skip picking commits whose parents are unchanged */
-static int skip_unnecessary_picks(struct object_id *output_oid)
+static int skip_unnecessary_picks(struct todo_list *todo_list,
+				  struct object_id *output_oid)
 {
-	const char *todo_file = rebase_path_todo();
-	struct strbuf buf = STRBUF_INIT;
-	struct todo_list todo_list = TODO_LIST_INIT;
 	struct object_id *parent_oid;
-	int fd, i;
-
-	if (!read_oneliner(&buf, rebase_path_onto(), 0))
-		return error(_("could not read 'onto'"));
-	if (get_oid(buf.buf, output_oid)) {
-		strbuf_release(&buf);
-		return error(_("need a HEAD to fixup"));
-	}
-	strbuf_release(&buf);
-
-	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
-		return -1;
-	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
-		todo_list_release(&todo_list);
-		return -1;
-	}
+	int i;
 
-	for (i = 0; i < todo_list.nr; i++) {
-		struct todo_item *item = todo_list.items + i;
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
 
 		if (item->command >= TODO_NOOP)
 			continue;
 		if (item->command != TODO_PICK)
 			break;
 		if (parse_commit(item->commit)) {
-			todo_list_release(&todo_list);
 			return error(_("could not parse commit '%s'"),
 				oid_to_hex(&item->commit->object.oid));
 		}
@@ -4666,37 +4635,21 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 		oidcpy(output_oid, &item->commit->object.oid);
 	}
 	if (i > 0) {
-		int offset = get_item_line_offset(&todo_list, i);
 		const char *done_path = rebase_path_done();
 
-		fd = open(done_path, O_CREAT | O_WRONLY | O_APPEND, 0666);
-		if (fd < 0) {
-			error_errno(_("could not open '%s' for writing"),
-				    done_path);
-			todo_list_release(&todo_list);
-			return -1;
-		}
-		if (write_in_full(fd, todo_list.buf.buf, offset) < 0) {
+		if (todo_list_write_to_file(todo_list, done_path, NULL, NULL, i, 0)) {
 			error_errno(_("could not write to '%s'"), done_path);
-			todo_list_release(&todo_list);
-			close(fd);
 			return -1;
 		}
-		close(fd);
 
-		if (rewrite_file(rebase_path_todo(), todo_list.buf.buf + offset,
-				 todo_list.buf.len - offset) < 0) {
-			todo_list_release(&todo_list);
-			return -1;
-		}
+		MOVE_ARRAY(todo_list->items, todo_list->items + i, todo_list->nr - i);
+		todo_list->nr -= i;
+		todo_list->current = 0;
 
-		todo_list.current = i;
-		if (is_fixup(peek_command(&todo_list, 0)))
-			record_in_rewritten(output_oid, peek_command(&todo_list, 0));
+		if (is_fixup(peek_command(todo_list, 0)))
+			record_in_rewritten(output_oid, peek_command(todo_list, 0));
 	}
 
-	todo_list_release(&todo_list);
-
 	return 0;
 }
 
@@ -4770,6 +4723,11 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 		return -1;
 	}
 
+	if (opts->allow_ff && skip_unnecessary_picks(&new_todo, &oid)) {
+		todo_list_release(&new_todo);
+		return error(_("could not skip unnecessary pick commands"));
+	}
+
 	if (todo_list_write_to_file(&new_todo, todo_file, NULL, NULL, -1,
 				    flags & ~(TODO_LIST_SHORTEN_IDS))) {
 		todo_list_release(&new_todo);
@@ -4778,12 +4736,9 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 
 	todo_list_release(&new_todo);
 
-	if (opts->allow_ff && skip_unnecessary_picks(&oid))
-		return error(_("could not skip unnecessary pick commands"));
-
 	if (checkout_onto(opts, onto_name, oid_to_hex(&oid), orig_head))
 		return -1;
-;
+
 	if (require_clean_work_tree("rebase", "", 1, 1))
 		return -1;
 

sequencer.c, sequencer.h

diff --git a/sequencer.c b/sequencer.c
index 07cc91d8db..7adbeaa27d 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1443,32 +1443,6 @@ static int allow_empty(struct replay_opts *opts, struct commit *commit)
 		return 1;
 }
 
-/*
- * Note that ordering matters in this enum. Not only must it match the mapping
- * below, it is also divided into several sections that matter.  When adding
- * new commands, make sure you add it in the right section.
- */
-enum todo_command {
-	/* commands that handle commits */
-	TODO_PICK = 0,
-	TODO_REVERT,
-	TODO_EDIT,
-	TODO_REWORD,
-	TODO_FIXUP,
-	TODO_SQUASH,
-	/* commands that do something else than handling a single commit */
-	TODO_EXEC,
-	TODO_BREAK,
-	TODO_LABEL,
-	TODO_RESET,
-	TODO_MERGE,
-	/* commands that do nothing but are counted for reporting progress */
-	TODO_NOOP,
-	TODO_DROP,
-	/* comments (not counted for reporting progress) */
-	TODO_COMMENT
-};
-
 static struct {
 	char c;
 	const char *str;
@@ -1939,26 +1913,7 @@ enum todo_item_flags {
 	TODO_EDIT_MERGE_MSG = 1
 };
 
-struct todo_item {
-	enum todo_command command;
-	struct commit *commit;
-	unsigned int flags;
-	const char *arg;
-	int arg_len;
-	size_t offset_in_buf;
-};
-
-struct todo_list {
-	struct strbuf buf;
-	struct todo_item *items;
-	int nr, alloc, current;
-	int done_nr, total_nr;
-	struct stat_data stat;
-};
-
-#define TODO_LIST_INIT { STRBUF_INIT }
-
-static void todo_list_release(struct todo_list *todo_list)
+void todo_list_release(struct todo_list *todo_list)
 {
 	strbuf_release(&todo_list->buf);
 	FREE_AND_NULL(todo_list->items);
@@ -2060,7 +2015,7 @@ static int parse_insn_line(struct todo_item *item, const char *bol, char *eol)
 	return !item->commit;
 }
 
-static int parse_insn_buffer(char *buf, struct todo_list *todo_list)
+int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list)
 {
 	struct todo_item *item;
 	char *p = buf, *next_p;
@@ -2158,7 +2113,7 @@ static int read_populate_todo(struct todo_list *todo_list,
 		return error(_("could not stat '%s'"), todo_file);
 	fill_stat_data(&todo_list->stat, &st);
 
-	res = parse_insn_buffer(todo_list->buf.buf, todo_list);
+	res = todo_list_parse_insn_buffer(todo_list->buf.buf, todo_list);
 	if (res) {
 		if (is_rebase_i(opts))
 			return error(_("please fix this using "
@@ -2189,7 +2144,7 @@ static int read_populate_todo(struct todo_list *todo_list,
 		FILE *f = fopen_or_warn(rebase_path_msgtotal(), "w");
 
 		if (strbuf_read_file(&done.buf, rebase_path_done(), 0) > 0 &&
-				!parse_insn_buffer(done.buf.buf, &done))
+				!todo_list_parse_insn_buffer(done.buf.buf, &done))
 			todo_list->done_nr = count_commands(&done);
 		else
 			todo_list->done_nr = 0;
@@ -4454,7 +4409,7 @@ int sequencer_add_exec_commands(const char *commands)
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4510,7 +4465,7 @@ int transform_todos(unsigned flags)
 	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
 		return error(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4596,7 +4551,7 @@ int check_todo_list(void)
 		goto leave_check;
 	}
 	advise_to_edit_todo = res =
-		parse_insn_buffer(todo_list.buf.buf, &todo_list);
+		todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
 
 	if (res || check_level == MISSING_COMMIT_CHECK_IGNORE)
 		goto leave_check;
@@ -4615,7 +4570,7 @@ int check_todo_list(void)
 		goto leave_check;
 	}
 	strbuf_release(&todo_file);
-	res = !!parse_insn_buffer(todo_list.buf.buf, &todo_list);
+	res = !!todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list);
 
 	/* Find commits in git-rebase-todo.backup yet unseen */
 	for (i = todo_list.nr - 1; i >= 0; i--) {
@@ -4697,7 +4652,7 @@ static int skip_unnecessary_picks(struct object_id *output_oid)
 
 	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
 		return -1;
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
 		todo_list_release(&todo_list);
 		return -1;
 	}
@@ -4785,7 +4740,7 @@ int complete_action(struct replay_opts *opts, unsigned flags,
 	if (strbuf_read_file(buf, todo_file, 0) < 0)
 		return error_errno(_("could not read '%s'."), todo_file);
 
-	if (parse_insn_buffer(buf->buf, &todo_list)) {
+	if (todo_list_parse_insn_buffer(buf->buf, &todo_list)) {
 		todo_list_release(&todo_list);
 		return error(_("unusable todo list: '%s'"), todo_file);
 	}
@@ -4893,7 +4848,7 @@ int rearrange_squash(void)
 
 	if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
 		return -1;
-	if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
+	if (todo_list_parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
 		todo_list_release(&todo_list);
 		return -1;
 	}
diff --git a/sequencer.h b/sequencer.h
index 660cff5050..84f813305f 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -72,6 +72,55 @@ enum missing_commit_check_level {
 int write_message(const void *buf, size_t len, const char *filename,
 		  int append_eol);
 
+/*
+ * Note that ordering matters in this enum. Not only must it match the mapping
+ * of todo_command_info (in sequencer.c), it is also divided into several
+ * sections that matter.  When adding new commands, make sure you add it in the
+ * right section.
+ */
+enum todo_command {
+	/* commands that handle commits */
+	TODO_PICK = 0,
+	TODO_REVERT,
+	TODO_EDIT,
+	TODO_REWORD,
+	TODO_FIXUP,
+	TODO_SQUASH,
+	/* commands that do something else than handling a single commit */
+	TODO_EXEC,
+	TODO_BREAK,
+	TODO_LABEL,
+	TODO_RESET,
+	TODO_MERGE,
+	/* commands that do nothing but are counted for reporting progress */
+	TODO_NOOP,
+	TODO_DROP,
+	/* comments (not counted for reporting progress) */
+	TODO_COMMENT
+};
+
+struct todo_item {
+	enum todo_command command;
+	struct commit *commit;
+	unsigned int flags;
+	const char *arg;
+	int arg_len;
+	size_t offset_in_buf;
+};
+
+struct todo_list {
+	struct strbuf buf;
+	struct todo_item *items;
+	int nr, alloc, current;
+	int done_nr, total_nr;
+	struct stat_data stat;
+};
+
+#define TODO_LIST_INIT { STRBUF_INIT }
+
+int todo_list_parse_insn_buffer(char *buf, struct todo_list *todo_list);
+void todo_list_release(struct todo_list *todo_list);
+
 /* Call this to setup defaults before parsing command line options */
 void sequencer_init_config(struct replay_opts *opts);
 int sequencer_pick_revisions(struct replay_opts *opts);

diff --git a/sequencer.c b/sequencer.c
index d726f77e11..a7afaf6882 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2091,6 +2091,8 @@ static int parse_insn_buffer(struct repository *r, char *buf,
 	char *p = buf, *next_p;
 	int i, res = 0, fixup_okay = file_exists(rebase_path_done());
 
+	todo_list->current = todo_list->nr = 0;
+
 	for (i = 1; *p; i++, p = next_p) {
 		char *eol = strchrnul(p, '\n');
 
@@ -2104,7 +2106,10 @@ static int parse_insn_buffer(struct repository *r, char *buf,
 		if (parse_insn_line(r, item, p, eol)) {
 			res = error(_("invalid line %d: %.*s"),
 				i, (int)(eol - p), p);
-			item->command = TODO_NOOP;
+			item->command = TODO_COMMENT + 1;
+			item->arg = p;
+			item->arg_len = (int)(eol - p);
+			item->commit = NULL;
 		}
 
 		if (fixup_okay)