[PATCH] Allow git-diff exit with codes similar to diff(1)

["Alex Riesen" <raa.lkml@gmail.com>]

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This introduces a new command-line option: --exit-code. The diff
programs will return 1 for differences, return 0 for equality, and
something else for errors.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
---
Updated the patch:

- added more tests: path limiter and -S
- moved exit code into diff_options and used diffcore_std* for its evaluation

On 3/14/07, Junio C Hamano <junkio@cox.net> wrote:
> > Challenging... Now, if someone just told me where to look for
> > differences in diff-tree case...
>
> As the resident git-diff expert I might hack on this myself as
> the --quiet options are useful, and --exit-code comes almost
> free when you properly do --quiet that implies --quick.

Thanks! That would _most_ welcome :)

> > Can it eventually be wired to "-s" (DIFF_FORMAT_NO_OUTPUT)?
>
> I do not think so.  When we run diff internally to pick the set
> of paths (i.e. run diffcore and check contents of diff_queue,
> just like you did for diff-index/diff-files), we internally use
> NO_OUTPUT.  See merge-recursive.c for an example.

Right, is not that simple as it looks...

> >> >       diffcore_std(&revs->diffopt);
> >> > +     ret = revs->diffopt.diff_exit_code && diff_queued_diff.nr ? 1: 0;
> >> >       diff_flush(&revs->diffopt);
> >> >       return ret;
> >> >  }
> >>
> >> This side looks correct, as you are counting queued_diff.nr after
> >> letting diffcore_std() to filter the results.
> >
> > And it will continue to work if the diffing is left early because of
> > no output needed. Err, will it?
>
> To implement --quick correctly, you need to know when it is safe
> to leave early.  Presence of -S (pickaxe) would most likely mean
> you shouldn't leave early.

Thanks, that got me thinking. Moved all exit code evaluation
into diffcore_std, added a field for the code to diff_options,
and use it if called with --exit-code.

 Documentation/diff-options.txt |    5 +++
 builtin-diff-files.c           |    4 ++-
 builtin-diff-index.c           |    4 ++-
 builtin-diff-tree.c            |    4 +-
 builtin-diff.c                 |   19 +++++++-----
 diff-lib.c                     |    5 ++-
 diff.c                         |    6 ++++
 diff.h                         |    5 ++-
 t/t4017-diff-retval.sh         |   64 ++++++++++++++++++++++++++++++++++++++++
 9 files changed, 102 insertions(+), 14 deletions(-)
 create mode 100755 t/t4017-diff-retval.sh

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