[PATCH v12 3/4] sequencer: share the squash message marker helpers and flags

From: Harald Nordgren via GitGitGadget <gitgitgadget@gmail.com>
Date: Aug 4, 2026, 08:30 UTC
Message-ID: <352db997e9da56b2d94eb98d8a90b9f90c0577e8.1785832251.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.2337.v12.git.git.1785832251.gitgitgadget@gmail.com>

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a "This is a combination of N commits." banner, a "This is the 1st/Nth commit message:" header above each kept message (or a "will be skipped" header for a dropped one), and a commented-out subject for any fixup!, squash! or amend! commit. The banner, the headers and the subject-commenting all live in static helpers in sequencer.c wired to the rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(), add_squash_message_header() (which takes a flag for the "will be skipped" variant) and squash_subject_comment_len(), and use them from update_squash_messages() and append_squash_message(). Also move the todo_item_flags enum to the header, so a caller reading the output of todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG) from a plain fixup!. A later change reuses all of this to give "git history squash" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 82ab3c536f..642dfa9d91 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2025,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2096,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2121,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2142,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,

-- 
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