bug#64055: [WIP Patch] Enable editing commit messages - vc-git-modify-change-comment

[Sean Whitton <spwhitton@spwhitton.name>]

Hello,

On Tue 13 Jun 2023 at 06:59pm -04, Morgan Smith wrote:

> diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
> index a3469b71386..18d6f1f47dc 100644
> --- a/lisp/vc/vc-git.el
> +++ b/lisp/vc/vc-git.el
> @@ -1384,6 +1384,24 @@ vc-git-clone
>      (vc-git--out-ok "clone" remote directory))
>    directory)
>
> +(defun vc-git-modify-change-comment (_files rev comment)
> +  "Modify the change comments on REV to COMMENT."
> +  ;; This is very similar to using to "git commit --fixup=amend"
> +  ;; command but it is more precise as it does the rebase matching
> +  ;; with the hash instead of the subject line.  Also we can't use
> +  ;; --fixup non-interactively (it doesn't support -m or -F) so this
> +  ;; is much easier.
> +  (vc-git-command nil 0 nil "commit"
> +                  "--allow-empty"
> +                  "-m" (concat "amend! " rev "\n\n" comment))
> +  ;; We should really be able to do this "non-interactively" but we
> +  ;; can't so we set GIT_SEQUENCE_EDITOR
> +  (let ((process-environment
> +         (cons
> +          "GIT_SEQUENCE_EDITOR=:"
> +          process-environment)))
> +    (vc-git-command nil 0 nil "rebase" "--autosquash" "-i" (concat rev "~1"))))
> +
>  ;;; HISTORY FUNCTIONS

A few notes here:

- We will need to ensure that the commit is actually empty, not just
  allow it to be empty.

  We have vc-git--stash-staged-changes we could use, but on my machine
  git-commit has --fixup=reword:... which is for amending only the
  commit message.  So probably use that.

- We will probably want to pass --autostash to git-rebase, too.

- It is probably best to set GIT_SEQUENCE_EDITOR=true so that we're not
  relying on the shell -- there is no /bin/:, but there is /bin/true.
  This is minor.

> @@ -1576,7 +1594,13 @@ vc-git-expanded-log-entry
>      (apply #'vc-git-command t nil nil
>             `("log"
>               ,revision
> -             "-1"  "--no-color" ,@(ensure-list vc-git-log-switches)
> +             "-1"  "--no-color"
> +             ;; The same as the default "medium" format but it doesn't
> +             ;; put spaces at the beginning of the body.  This is so
> +             ;; we can grab this as the initial value when calling
> +             ;; log-view-modify-change-comment
> +             "--pretty=format:commit %H%nAuthor: %an %ae%nDate:   %ad%n%n%B"
> +             ,@(ensure-list vc-git-log-switches)
>               "--"))
>      (goto-char (point-min))
>      (unless (eobp)

I think it's preferable to use a vc-git--extract-comment as in the patch
I just posted.

-- 
Sean Whitton