Re: Possible bug regarding trailers

From: Christian Couder <christian.couder@gmail.com>
Date: Jun 16, 2023, 18:37 UTC
Message-ID: <CAP8UFD22tPfP37LU8tveHmZPzj7rwUnsEzctzRdqYripv2cyjg@mail.gmail.com>
In-Reply-To: <PH7PR07MB9467AD34C96AEE60D5A4369F8C58A@PH7PR07MB9467.namprd07.prod.outlook.com>

On Fri, Jun 16, 2023 at 6:04 PM eric.frederich@siemens.com <eric.frederich@siemens.com> wrote:

Show 6 quoted lines

>
> Thanks for the reply and finding that code.
> I'm wondering a couple of things.
>
> A)
> Is it reasonable to expect that a trailer added during commit with `git commit --trailer some-key:some-value` always be able to be retrieved regardless of the contents of the commit message?

I think the following 3 conditions would be needed:

  - `git commit --trailer ...` should be fixed using a patch like the
one Peff proposed, and the trailer should be added using this fixed
command,
  -  a command that outputs only a commit message, or perhaps commits
headers and the commit message, like `git cat-file commit rev`, should
be used to retrieve the commit message that is passed to `git
interpret-trailers` for retrieving the trailer,
  - and `git interpret-trailers` should be used with both --parse and
--no-divider.

> I am migrating source code history from an older SCM to Git and would like to preserve the change messages.

Have you looked at existing tools to do that (like maybe reposurgeon)?

Show 7 quoted lines

> B)
> Should anything that is retrieved via:
>     `git cat-file commit $SHA | git interpret-trailers --parse`
> also be displayed via:
>    `git log -1 --format="%(trailers:key=some-key,valueonly,separator=%x2c) %H %T" $SHA`
>
> ... why is there a difference?  (Explicit call to interpret-trailers shows the trailer, but the log command does not).

I believe Peff explained that.

> With some minimal investigation (I added a printf at the top of find_patch_start), I noticed that find_patch_start is called during call to `git interpret-trailers` but it is NOT called during call to `git log`.
> This means the same code paths are not being followed in those two cases dealing w/ trailers.
> I would expect that it should use the same code paths in both cases.

The log command shows all the content of the commit message as is, without any parsing. So yeah it doesn't use interpret-trailers' code which is useful for modifying or parsing trailers contained in commit messages.