--reset-author does not reset author date when used in post-commit hook

> device time zone is not UTC0
> 
> post-commit hook:
> if [[ -n "${SKIP_POST_COMMIT+x}" ]] && [[ "$SKIP_POST_COMMIT" -eq 1 ]]
> then
> exit
> fi
> 
> TZ=UTC0 SKIP_POST_COMMIT=1 git commit --amend --reset-author --no-edit
> --no-verify --no-post-rewrite --allow-empty --quiet
> 
> ---
> 
> Run:
> git commit -m "foo"
> git show -s --format="Commit: %h%nAuthor: %an%nAuthor Date:
> %ad%nCommitter: %cn%nCommitter Date: %cd%nMessage: %s%n" HEAD
> 
> Expected that both Author Date: and Committer Date: show +0000 as
> timezone. Only committer date shows +0000, while author date shows
> time zone of device.
> 
> When manually running the post-commit code (TZ=UTC0 SKIP_POST_COMMIT=1
> ...) it correctly resets the author date to +0000 too
> 
> When manually setting the date using --date="$(date +%s) +0000"
> instead of  --reset-author it also works correctly in post-commit
> hook.

>
> On 2025-03-31 at 20:19:30, Devste Devste wrote:
> > device time zone is not UTC0
> >
> > post-commit hook:
> > if [[ -n "${SKIP_POST_COMMIT+x}" ]] && [[ "$SKIP_POST_COMMIT" -eq 1 ]]
> > then
> > exit
> > fi
> >
> > TZ=UTC0 SKIP_POST_COMMIT=1 git commit --amend --reset-author --no-edit
> > --no-verify --no-post-rewrite --allow-empty --quiet
> >
> > ---
> >
> > Run:
> > git commit -m "foo"
> > git show -s --format="Commit: %h%nAuthor: %an%nAuthor Date:
> > %ad%nCommitter: %cn%nCommitter Date: %cd%nMessage: %s%n" HEAD
> >
> > Expected that both Author Date: and Committer Date: show +0000 as
> > timezone. Only committer date shows +0000, while author date shows
> > time zone of device.
> >
> > When manually running the post-commit code (TZ=UTC0 SKIP_POST_COMMIT=1
> > ...) it correctly resets the author date to +0000 too
> >
> > When manually setting the date using --date="$(date +%s) +0000"
> > instead of  --reset-author it also works correctly in post-commit
> > hook.
>
> I can reproduce this, except that I had to use `TZ=America/Toronto`
> since my system is in UTC.  A quick look at the code led me to a guess
> that ended up correct.
>
> The `git commit` code sets `GIT_AUTHOR_NAME`, `GIT_AUTHOR_EMAIL`, and
> `GIT_AUTHOR_DATE`.  The latter contains a timezone identifier.  As a
> consequence, when the hook is invoked, those values are set in the
> environment, and the subsequent `git commit` in the hook uses them.  You
> can see this by placing something like `env >/tmp/foo` in your hook and
> then reading the output.
>
> I will say that this is definitely not the intended use of the
> post-commit hook and I am very much not surprised that this doesn't work
> as you intended.  You could certainly fix it by unsetting those
> environment variables, but I'd encourage you to adopt a different
> approach, such as by using an alias that sets `TZ=UTC0` to commit.  That
> will be more likely to work in the future and will definitely be less
> brittle.
>
> For instance, your call to `git commit` will still invoke the
> `prepare-commit-msg` (and possibly `commit-msg`) hook, which might
> result in unexpected changes to your message or even a failure of the
> second commit.
> --
> brian m. carlson (they/them)
> Toronto, Ontario, CA

> >your call to `git commit` will still invoke the
> `prepare-commit-msg` (and possibly `commit-msg`) hook
> 
> Since I used --no-edit --no-verify in the example/hook, that shouldn't
> be the case though?

> >such as by using an alias that sets `TZ=UTC0` to commit.
> 
> Unfortunately, (at least on Windows) most tools and IDEs don't even
> load a bashrc file (e.g. intellij) for their git UI, so that's not an
> option (and setting the TZ as a global environment variable has
> unwanted side effects, since it will set the timezone in various
> applications randomly, e.g. Electron/Slack will use the TZ for some
> but not for other things,...)

>
> On 2025-04-01 at 03:44:17, Devste Devste wrote:
> > >your call to `git commit` will still invoke the
> > `prepare-commit-msg` (and possibly `commit-msg`) hook
> >
> > Since I used --no-edit --no-verify in the example/hook, that shouldn't
> > be the case though?
>
> My testing demonstrates that `commit-msg` is skipped with `--no-edit
> --no-verify`, but not `prepare-commit-msg`.
>
> > >such as by using an alias that sets `TZ=UTC0` to commit.
> >
> > Unfortunately, (at least on Windows) most tools and IDEs don't even
> > load a bashrc file (e.g. intellij) for their git UI, so that's not an
> > option (and setting the TZ as a global environment variable has
> > unwanted side effects, since it will set the timezone in various
> > applications randomly, e.g. Electron/Slack will use the TZ for some
> > but not for other things,...)
>
> What I could recommend instead is setting a shell script or PowerShell
> file or such as the default Git binary (instead of git.exe) and setting
> `TZ=UTC0` in that script (possibly only if the command is `commit` or
> `commit-tree`).  I use Neovim with the fugitive extension, and
> it provides functionality to override the Git executable, so I suspect
> other editors will as well.  This is something that will likely be
> robust and unlikely to break.
>
> The reason I make that recommendation is that I suspect you're going to
> find that there are other infelicities or weird edge cases in what
> you're doing and this would be a use case that I could see getting
> broken accidentally.  We've accidentally broken people doing `git add`
> in `pre-commit` hooks (which we also don't recommend) in the past, for
> instance.
> --
> brian m. carlson (they/them)
> Toronto, Ontario, CA