Re: [PATCH] interpret-trailers: obey scissors lines

Brian Malehorn [off-list ref] writes:

If a commit message is being edited as "verbose", it will contain a
scissors string ("-- >8 --") and a diff:

    my subject

    # ------------------------ >8 ------------------------
    # Do not touch the line above.
    # Everything below will be removed.
    diff --git a/foo.txt b/foo.txt
    index 5716ca5..7601807 100644
    --- a/foo.txt
    +++ b/foo.txt
    @@ -1 +1 @@
    -bar
    +baz

interpret-trailers doesn't interpret the scissors and therefore places
trailer information after the diff. A simple reproduction is:

    git config commit.verbose true
    GIT_EDITOR='git interpret-trailers --in-place --trailer Acked-by:me' \
        git commit --amend

This commit resolves the issue by teaching "git interpret-trailers" to
obey scissors the same way "git commit" does.

I'd prefer to see s/obey scissors lines/honor the cut line/, and the
last paragraph rephrased somewhat, perhaps like:

        Subject: interpret-trailers: honor the cut line

        If a commit message is edited with the "verbose" option, the
        buffer will have a cut line and diff after the log message,
        like so:

             my subject

             # ------------------------ >8 ------------------------
             # Do not touch the line above.
             # Everything below will be removed.
             diff --git a/foo.txt b/foo.txt
             index 5716ca5..7601807 100644
             --- a/foo.txt
             +++ b/foo.txt
             @@ -1 +1 @@
             -bar
             +baz

        "git interpret-trailers" is unaware of the cut line, and
        assumes the trailer block would be at the end of the whole
        thing.  This can easily be seen with:

             $ GIT_EDITOR='git interpret-trailers --in-place --trailer Acked-by:me' \
               git commit --amend -v

        Teach "git interpret-trailers" to notice the cut-line and
        ignore the remainder of the input when looking for a place
        to add new trailer block.  This makes it consistent with how
        "git commit -v -s" inserts a new Signed-off-by: line.

        This can be done by the same logic as the existing helper
        function, wt_status_truncate_message_at_cut_line(), uses,
        but it wants the caller to pass a strbuf to it.  Because the
        helper function ignore_non_trailer() used by the command
        takes a <pointer, length> pair, not a strbuf, steal the
        logic from wt_status_truncate_message_at_cut_line() to
        create a new wt_status_strip_scissors() helper function that
        takes <poiter, length> pair, and make ignore_non_trailer()
        call it to help "interpret-trailers".  Since there is only
        one caller of wt_status_truncate_message_at_cut_line() in
        cmd_commit(), rewrite it to call wt_status_strip_scissors()
        helper instead and remove the old helper that no longer has
        any caller.

The last paragraph would have saved me from getting puzzled.

The mention of "'commit -v -s' works that way, too" was my attempt
to justify why it is OK to make this change unconditionally to
intepret-trailers, but I am still not 100% convinced with that
reasoning (or your original log message) that it is a safe thing to
do.  It is not like its sole purpose is to serve as GIT_EDITOR for
the "git commit" command.

The patch text itself looks sensible.  

We still need to see your patch with your sign-off, though.

Thanks.