Subject: Re: bug & patch: exit codes from internal commands are handled incorrectly

From: Junio C Hamano <[email-masked]>
Date: Thu, 18 Dec 2014 11:18:32 -0800

Kenneth Lorber <[email-masked]> writes:

>> Bug: exit codes from (at least) internal commands are handled incorrectly.
>> E.g. git-merge-file, docs say:
>>        The exit value of this program is negative on error, and the number of
>>        conflicts otherwise. If the merge was clean, the exit value is 0.
>> But only 8 bits get carried through exit, so 256 conflicts gives
>> exit(0), which means the merge was clean.

Wouldn't any cmd_foo() that returns negative to main() be buggy?

Your change sweeps such problems under the rug, which is not a
healthy thing to do.

Expecting that the exit code can signal small positive integers and
other generic kinds of failures is a losing proposition.  I think it
is a better fix to update cmd_merge_file() to return 1 (when ret is
positive), 0 (when ret is zero) or 128 (when ret is negative), or
something simple like that, and update the documentation to match
that, without touching git.c::main().

Among the in-tree users, I notice git-cvsserver.perl is already
using the command incorrectly.  It does this:

            my $return = system("git", "merge-file", $file_local, $file_old, $file_new);
            $return >>= 8;

            cleanupTmpDir();

            if ( $return == 0 )
            {
                $log->info("Merged successfully");
                ...
            }
            elsif ( $return == 1 )
            {
                $log->info("Merged with conflicts");
                ...
            }
            else
            {
                $log->warn("Merge failed");
                next;
            }

which assumes $return == 1 is special "half-good", which is not
consistent with the documented interface.  It will incorrectly
say "Merge failed" when there are two or more conflicts.

And with such a "1 or 0 or -1" change, you will fix that caller as
well ;-)