Re: [PATCH v8 1/2] [GSOC] commit: add --trailer option

On Wed, Mar 17 2021, ZheNing Hu wrote:

Ævar Arnfjörð Bjarmason [off-list ref] 于2021年3月16日周二 下午8:52写道：

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+             if (run_command(&run_trailer))
+                     strvec_clear(&run_trailer.args);

This is git-commit, shouldn't we die() here instead of ignoring errors
in sub-processes?

After thinking about it carefully, your opinion is more
reasonable, because if the user uses the wrong `--trailer`
and does not get the information he needs, I think he will
have to use `--amend` to modify, and `die()` can exit
this commit directly.

Yeah, we don't want to silently lose data.

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+             strvec_clear(&trailer_args);
+     }
+
      /*
       * Reject an attempt to record a non-merge empty commit without
       * explicit --allow-empty. In the cherry-pick case, it may be

@@ -1507,6 +1529,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
              OPT_STRING(0, "fixup", &fixup_message, N_("commit"), N_("use autosquash formatted message to fixup specified commit")),
              OPT_STRING(0, "squash", &squash_message, N_("commit"), N_("use autosquash formatted message to squash specified commit")),
              OPT_BOOL(0, "reset-author", &renew_authorship, N_("the commit is authored by me now (used with -C/-c/--amend)")),
+             OPT_CALLBACK_F(0, "trailer", NULL, N_("trailer"), N_("trailer(s) to add"), PARSE_OPT_NONEG, opt_pass_trailer),
              OPT_BOOL('s', "signoff", &signoff, N_("add a Signed-off-by trailer")),

Not required for this change, but perhaps a change here to N_() (if we
can get it to fit) + doc update saying that we prefer
--trailer="Signed-Off-By: to --signoff"? More on that later.

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              OPT_FILENAME('t', "template", &template_file, N_("use specified template file")),
              OPT_BOOL('e', "edit", &edit_flag, N_("force edit of commit")),

diff --git a/t/t7502-commit-porcelain.sh b/t/t7502-commit-porcelain.sh
index 6396897cc818..0acf23799931 100755
--- a/t/t7502-commit-porcelain.sh
+++ b/t/t7502-commit-porcelain.sh

@@ -154,6 +154,26 @@ test_expect_success 'sign off' '

 '

+test_expect_success 'trailer' '
+     >file1 &&
+     git add file1 &&
+     git commit -s --trailer "Signed-off-by:C O Mitter1 <committer1@example.com>" \
+             --trailer "Helped-by:C O Mitter2 <committer2@example.com>"  \
+             --trailer "Reported-by:C O Mitter3 <committer3@example.com>" \
+             --trailer "Mentored-by:C O Mitter4 <committer4@example.com>" \
+             -m "hello" &&
+     git cat-file commit HEAD >commit.msg &&
+     sed -e "1,7d" commit.msg >actual &&
+     cat >expected <<-\EOF &&
+     Signed-off-by: C O Mitter <committer@example.com>
+     Signed-off-by: C O Mitter1 <committer1@example.com>
+     Helped-by: C O Mitter2 <committer2@example.com>
+     Reported-by: C O Mitter3 <committer3@example.com>
+     Mentored-by: C O Mitter4 <committer4@example.com>
+     EOF
+     test_cmp expected actual
+'
+

How does this interact with cases where the user has configured
"trailer.separators" to have a value that doesn't contain ":"?  I
haven't tested, but my reading of git-interpret-trailers(1) is that if
you supplied "=" instead that case would just work:

    By default only : is recognized as a trailer separator, except that
    = is always accepted on the command line for compatibility with
    other git commands.

But interpret_trailers interface allow us use "=" instead of other separators.

I did a simple test and modified the configuration "trailer.separators"
and it still works. Now things are good here:

$ git -c trailer.separators="@" commit --trailer="Signed-off-by=C O <email>"

or

$ git -c trailer.separators="@" commit --trailer="Signed-off-by@C O <email>"

Both can work normally,

--trailer="Signed-off-by@ C O <email>"

will output in the commit message.

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I don't know if that does the right thing in the presence of
--if-exists=add.

Yesterday, Christian Couder and I had already discussed this issue:
Your idea is correct, I should not add "--if-exists = add",  this will destroy
the user's rights to configure by using `git -c trailer.if-exist`.

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So it would be good to update these tests so you test:

 * For the --if-exists=add case at all, there's no tests for it
   now. I.e. add some trailers manually to the commit (via -F or
   whatever) and then see if they get added to, replacet etc.

 * Ditto but for the user having configured trailer.separators (see the
   test_config helper for how to set config in a test). I.e. if it's "="
   does adding trailers work, how about if it's "=" on the CLI but the
   config/commit message has ";" instead of ":" or something?

As mentioned above, it works normally.

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 * Hrm, actually I think tweaking "-c trailer.ifexists" won't work at
   all, since the CLI switch would override it. I honestly don't know,
   but why not not supply it and keep the addIfDifferentNeighbor
   default?

   If it's essential that seems like a good test / documentation
   addition...

 * For the above -c ... case I can't think of a good way to deal with it
   that doesn't involve pulling in git_trailer_config() into
   git_commit_config(), but perhaps the least nasty way is to just set a
   flag in git_commit_config() if we see a "trailer.ifexists" flag, and
   if so don't provide "--if-exists=add", if there's no config (this
   will include "git -c ... commit" we set provide "--if-exists=add" )
   or as noted above, maybe we can skip the whole thing and use the
   addIfDifferentNeighbor default.

Has been restored to the default settings.

To clarify: What I really mean is for all these things you've tested:
let's add those to the tests as part of the patch.

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And, not needed for this patch but worth thinking about:

 * We pass through --trailer to git-interpret-trailers, what should we
   do about the other options? Should git-commit eventually support
   --trailer-where and pass it along as --where to
   git-interpret-trailers, or is "git -c trailer.where=... commit" good
   enough?

Logically speaking, `interpret_trailers` should be dedicated to `commit`
or other sub-commands that require trailers.

But I think that in the later stage, the parse_options of the `cmd_commit`
can keep the unrecognized options, and then these choices can be directly
passed to the `interpret_trailers` backend.

We have this interaction with e.g. range-diff and "log", it's often
surprising. You add an option to one command and it appears in the
other.

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 * It would be good to test for and document if that "-c trailer.*"
   trick works (no reason it shouldn't). I.e. to add something like this
   after what you have (along with tests, and check if it's even true):

I haven't tested them for the time being, but I will do it.

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       Only the `--trailer` argument to
       linkgit:git-interpret-trailers[1] is supported. Other
       pass-through switches may be added in the future, but currently
       you'll need to pass arguments to
       linkgit:git-interpret-trailers[1] along as config, e.g. `git -c
       trailer.where=start commit [...] --trailer=[...]`.

I think this is worth writing in the documentation.

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 * We have a longer-term goal of having the .mailmap apply to trailers,
   it would be nice if git-interpret-trailers had some fuzzy-matching to
   check if the RHS of a trailer is a name/E-Mail pair, and if so did
   stricter validation on it with the ident functions we use for fsck
   etc. (that's copied & subtly different in several different places in
   the codebase, unfortunately[1]).

I may not know much about fuzzy-matching, which may be worth studying later.

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More thoughts:

 * Having written all the above I checked how --signoff is implemented.

   It seems to me to be a good idea to (at least for testing) convert
   the --signoff trailer to your implementation. We have plenty of tests
   for it, does migrating it over pass or fail those?

I don’t know how to migrating yet, it may take a long time.
Even I think I can leave it as #leftoverbit later.

Sure, I mean (having looked at it) that at least for your own local
testing it would make sense to change it (even if just search-replacing
the --signoff in the test suite) to see if it behaves as you
expect. I.e. does the --trailer behavior mirror --signoff?

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 * I also agree with Junio that we shouldn't have a --fixed-by or
   whatever and wouldn't add --signoff today, but it seems very useful
   to me to have a shortcut like:

       --trailer "Signed-off-by"

   I.e. omitting the value, or:

      --trailer "Signed-off-by="

   Or some other thing we deem sufficiently useful/sane
   syntax/unambiguous.n

   Then the value would be provided by fmt_name(WANT_COMMITTER_IDENT)
   just as we do in append_signoff() now. I think a *very common* case
   for this would be something like:

       git commit --amend -v --trailer "Reviewed-by"

   And it would be useful to help that along and not have to do:

       git commit --amend -v --trailer "Reviewed-by=$(git config user.name) <$(git config user.email)>"

   Or worse yet, manually typo your name/e-mail address, as I'm sure I
   and many others will inevitably do when using this option...

I think this idea is very good and easy to implement.
We only need to do a simple string match when we get the "trailer" string,
If it can be completed, it can indeed bring great convenience to users.

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1. https://lore.kernel.org/git/87bld8ov9q.fsf@evledraar.gmail.com/ (local)

Thanks, Ævar Arnfjörð Bjarmason!

And thanks for working on this.