[PATCH v6 0/2] rebase -i: extend rebase.missingCommitsCheck

To prevent mistakes when editing a branch, rebase features a knob, rebase.missingCommitsCheck, to warn the user if a commit was dropped. Unfortunately, this check is only effective for the initial edit, which means that if you edit the todo list at a later point of the rebase and drop a commit, no warnings or errors would be issued.

This adds the ability to check if commits were dropped when editing the todo list with `--edit-todo', and when resuming a rebase.

The first patch moves moves check_todo_list_from_file() and `edit_todo_list_advice' from sequencer.c to rebase-interactive.c so the latter can be used by edit_todo_list() and todo_list_check(). The second patch adds the check to `--edit-todo' and `--continue' and tests.

This is based on 26027625dd ("rebase -i: also avoid SHA-1 collisions with missingCommitsCheck", 2020-01-23).

The tip of this series is tagged as "edit-todo-drop-v6" at https://github.com/agrn/git.

Changes since v5:

 - Rebased onto js/rebase-i-with-colliding-hash.  This means the backup
   is once again created with todo_list_write_to_file(), but without the
   flag `TODO_LIST_SHORTEN_IDS' this time.

Alban Gruin (2):
  sequencer: move check_todo_list_from_file() to rebase-interactive.c
  rebase-interactive: warn if commit is dropped with `rebase
    --edit-todo'

 rebase-interactive.c          |  84 ++++++++++++++++++++---
 rebase-interactive.h          |   5 ++
 sequencer.c                   |  51 ++++----------
 sequencer.h                   |   2 +-
 t/t3404-rebase-interactive.sh | 121 ++++++++++++++++++++++++++++++++++
 5 files changed, 214 insertions(+), 49 deletions(-)

Range-diff against v5:
1:  996045a300 = 1:  4f07ce94a8 sequencer: move check_todo_list_from_file() to rebase-interactive.c
2:  6dbaa8cbe6 ! 2:  68481d89b0 rebase-interactive: warn if commit is dropped with `rebase --edit-todo'
    @@ rebase-interactive.c: int edit_todo_list(struct repository *r, struct todo_list
      				    -1, flags | TODO_LIST_SHORTEN_IDS | TODO_LIST_APPEND_TODO_HELP))
      		return error_errno(_("could not write '%s'"), todo_file);
      
    --	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());
    -+	if (initial || !incorrect) {
    -+		if (!initial)
    -+			unlink(todo_backup);
    -+
    -+		if (copy_file(todo_backup, todo_file, 0666))
    -+		    return error(_("could not copy '%s' to '%s'."), todo_file, todo_backup);
    -+	}
    - 
    - 	if (launch_sequence_editor(todo_file, &new_todo->buf, NULL))
    - 		return -2;
    +-	if (initial &&
    +-	    todo_list_write_to_file(r, todo_list, rebase_path_todo_backup(),
    ++	if (!incorrect &&
    ++	    todo_list_write_to_file(r, todo_list, todo_backup,
    + 				    shortrevisions, shortonto, -1,
    + 				    (flags | TODO_LIST_APPEND_TODO_HELP) & ~TODO_LIST_SHORTEN_IDS) < 0)
    + 		return error(_("could not write '%s'."), rebase_path_todo_backup());
     @@ rebase-interactive.c: int edit_todo_list(struct repository *r, struct todo_list *todo_list,
      	if (initial && new_todo->buf.len == 0)
      		return -3;
    @@ sequencer.c: int sequencer_continue(struct repository *r, struct replay_opts *op
     +			unlink(rebase_path_dropped());
     +		}
     +
    - 		if (commit_staged_changes(r, opts, &todo_list))
    - 			return -1;
    - 	} else if (!file_exists(get_todo_path(opts)))
    + 		if (commit_staged_changes(r, opts, &todo_list)) {
    + 			res = -1;
    + 			goto release_todo_list;
     @@ sequencer.c: int todo_list_write_to_file(struct repository *r, struct todo_list *todo_list,
      	return res;
      }