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

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

>> If a commit message is being editted 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

So, "git commit --amend --verbose" prepares something like the above
example and passes it to the GIT_EDITOR.  The problem description
indicates that because interpret-trailers (which happens to be used
as the GIT_EDITOR) treats the cut-line used by "git commit" just
like any other random line, it tries to find the trailer block way
below, in the patch text.  I agree that it is a problem.  But...

>> diff --git a/builtin/commit.c b/builtin/commit.c
>> index 2de5f6cc6..2ce9c339d 100644
>> --- a/builtin/commit.c
>> +++ b/builtin/commit.c
>> @@ -1735,7 +1735,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
>>  
>>  	if (verbose || /* Truncate the message just before the diff, if any. */
>>  	    cleanup_mode == CLEANUP_SCISSORS)
>> -		wt_status_truncate_message_at_cut_line(&sb);
>> +		strbuf_setlen(&sb,
>> +			      wt_status_last_nonscissors_index(sb.buf, sb.len));
>
> This hunk surprised me at first (that we would need to touch commit.c at
> all), but the refactoring makes sense.

This still surprises me.  If the problem is in interpret-trailers,
why do we even need to touch cmd_commit()?  If GIT_EDITOR returns us

     my subject
 
     Acked-by: me
     # ------------------------ >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

after this patch fixes interpret-trailers, wouldn't the cmd_commit()
function work as expected without any change?

Puzzled.

The proposed log message calls the cut-line "scissors", but that is
probably a source of this confusion.  The cut-line and scissors do
not have much in commmon.  For one thing, scissors is a mechanism to
discard everything _ABOVE_ it.  The cut-line we see in this example,
on the other hand, is about discarding everything _BELOW_ it.