Re: Skipping adding Signed-off-by even if it's not the last on git commit

[Jeff King <peff@peff.net>]

On Thu, Dec 08, 2022 at 08:04:46AM +0900, Junio C Hamano wrote:

> Taylor Blau <me@ttaylorr.com> writes:
> 
> >> > >     $ git commit --signoff[=[no-]dedup]
> > ...
> > Thanks, I look forward to seeing your work. It would be nice to
> > standardize on this `--signoff[=[no-]dedup]` thing throughout all of the
> > different commands that support it.
> 
> Also, if I am not mistaken, each of trailers can be configured to
> have its own semantics (e.g. .where and .ifExists).
> 
>  * Should we have similar override to these trailer tokens, not just
>    sign-off?

This made me curious about the opposite: is there config you can set to
get this behavior for --signoff? I think the answer is "no". You can do:

  git -c trailer.ifExists=addIfDifferent \
      commit --amend --trailer="Signed-off-by: Jeff King <peff@peff.net>"

to get the desired behavior, but using "--signoff" does not respect
trailer settings.

I feel like config is probably a better match for the use cases here,
because the decision about de-duping is not something you'd usually set
for one particular operation, but is more likely to be a project policy
about what the trailer means (and that includes Signed-off-by). So you'd
want to set it per-repo, not per-operation.

>  * Should we offer not just [no-]dedup (which is equivalent to
>    switching from addIfDifferentNeighbor to addIfDifferent) but
>    other customization?  This affects what --signoff should be
>    allowed to take for consistency across trailers.

Yeah, writing the above made me wonder if --signoff should behave
exactly like:

  --trailer="Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>"

For the most part that would not change any behavior unless you set
trailer.signed-off-by.*, and setting those presumably signals intent
that you expect them to take effect. The one exception is that the
generic trailer.ifExists, etc, would start affecting --signoff, which
_might_ be a surprise. If we wanted to retain the behavior there, we
could say "--signoff is special, and doesn't respect generic trailer
config".

Alternatively, it would be nice if there was an easy way to put your
ident into a trailer (what I wrote above doesn't really work unless you
have those variables in your environment, and of course it's a lot of
typing). I think you can hack it up like:

  git config trailer.sign.key Signed-off-by
  git config trailer.sign.cmd \
    'git var GIT_COMMITTER_IDENT | sed "s/>.*/>/";:'
  git commit --trailer=sign

which is only a little more typing than --signoff, but it's not very
ergonomic.

-Peff