Re: Non-interactively rewording commit messages

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Konstantin,

On Thu, 30 Jun 2022, Konstantin Ryabitsev wrote:

> What's the best approach to non-interactively rewrite specific commit
> messages? In this particular case, I am trying to automatically retrieve code
> review trailers sent to the mailing list and put them into corresponding
> commits.
>
> For example, I have a set of commits:
>
> abcabc: This commit does foo
> bcdbcd: This commit does bar
> cdecde: This commit does baz
>
> They were all sent to the mailing list and a maintainer sent a "Reviewed-by"
> to the second commit. In a usual interactive rebase session this would be:
>
> pick abcabc
> reword bcdbcd
> pick cdecde
>
> When the edit screen comes up for the bcdbcd commit, the author would manually
> stick the new trailer into the commit message. However, I can automate all
> that away with b4 -- just need a sane strategy for non-interactively rewriting
> entire commit messages at arbitrary points in the recent history.
>
> Any pointers?

The quickest (in terms of script size) might be to craft an `amend!`
commit, something like this:

	git commit --allow-empty -m "$(printf 'amend! bcdbcd\n\n' &&
		git cat-file commit bcdbcd |
		sed -e '1,/^$/d' \
		 -e '{:1;${s/^/Reviewed-by: M A Intainer <maintainer@example.org>\n/;b};N;/\n$/b;b1}')"

and then running an "interactive" rebase with `:` as the editor:

	GIT_SEQUENCE_EDITOR=: GIT_EDITOR=: git rebase -i --autosquash HEAD~3

(The `sed` call is admittedly a bit horrible, it prepends the
`Reviewed-by:` footer to the last paragraph, if it needs to be _appended_,
it can be greatly simplified.)

Ciao,
Dscho