bug#38044: 27.0.50; There should be an easier way to look at a specific vc commit

[Stephen Berman]

On Sun, 03 Nov 2019 16:17:05 +0100 Lars Ingebrigtsen <larsi@gnus.org> wrote:

> Often when discussing code changes, people will send an email saying
> something like "this was fixed by <id>", but Emacs doesn't have a
> convenient way to display that.
>
> For that case, Emacs should have a command that prompts for an ID
> (defaulting to the ID under point), and then (unless default-directory
> is already in a vc-controlled directory), prompts for the directory to
> look for that ID, and then display the commit.

I wrote such a command (appended below) for my own use, but it's
git-specific and I don't know the innards of VC well enough to adapt it,
which is why I haven't proposed it for inclusion in Emacs.  Maybe some
of it could be used for a VC command.

Steve Berman


(defun srb-git-log (&optional repo commit)
  "Check REPO for COMMIT and if it exists, display its commit message.
Interactively, prompt for REPO, defaulting to emacs-master, and
for COMMIT, defaulting to the commit hash at point.  If called
with a prefix argument `C-u', show the commit diff in addition to
the commit message."
  (interactive "P")
  (let* ((show (equal current-prefix-arg '(4)))
         (git-dir (if repo
                      (read-directory-name "Repo: " "~/src/emacs/"
                                           nil t "emacs-master")
                    "~/src/emacs/emacs-master"))
         (commit0 (substring-no-properties
                   (or commit
                       (read-string "Commit: " nil nil (word-at-point)))))
         (default-directory git-dir)
         (output-buffer (get-buffer-create "*git log*"))
         (args (split-string (mapconcat #'concat
                                        (if show
                                            `("show" ,commit0)
                                          `("log" "-1" ,commit0)) " ")))
         ;; FIXME: output of `git branch --contains' can be ambiguous (even
         ;; when `git log isn't, because one hash is for a commit, one for a
         ;; tree?).  Can use `git rev-parse --disambiguate=' to find matching
         ;; full hashes.
         (proc (progn
                 (with-current-buffer output-buffer (erase-buffer))
                 (call-process "git" nil output-buffer nil
                               "branch" "--contains" commit0))))
    (when proc
      (with-current-buffer output-buffer
        (goto-char (point-min))
        (unless (looking-at "[ *]")
          (user-error "%s is not on branch %s" commit0
                      (file-name-base git-dir)))
        (insert "Branches:\n")
        (goto-char (point-max))
        (apply #'call-process "git" nil output-buffer nil args)
        (when show
          (with-current-buffer output-buffer
            (diff-mode)))
        (pop-to-buffer output-buffer)))))