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

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 <redacted>
---
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 [off-list ref] wrote:

quoted

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 :)

quoted

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...

quoted

quoted

quoted

      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