merge-file: clamp exit code to maximum 127

Git-merge-file is documented to return one of three exit
codes:

  - zero means the merge was successful

  - a negative number means an error occurred

  - a positive number indicates the number of conflicts

Unfortunately, this all gets stuffed into an 8-bit return
code. Which means that if you have 256 conflicts, this wraps
to zero, and the merge appears to succeed (and commits a
blob full of conflict-marker cruft!).

This patch clamps the return value to a maximum of 127,
which we should be able to safely represent everywhere. This
also leaves 128-255 for other values. Shells (and some parts
of git) will typically represent signal death as 128 plus
the signal number. And negative values are typically coerced
to an 8-bit unsigned value (so "return -1" ends up as 255).

Technically negative returns have the same problem (e.g.,
"-256" wraps back to 0), but this is not a problem in
practice, as the only negative value we use is "-1".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/git-merge-file.txt b/Documentation/git-merge-file.txt
index d2fc12ec77..f856032613 100644
--- a/Documentation/git-merge-file.txt
+++ b/Documentation/git-merge-file.txt
@@ -41,7 +41,8 @@ lines from `<other-file>`, or lines from both respectively.  The length of the
 conflict markers can be given with the `--marker-size` option.
 
 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.
+conflicts otherwise (truncated to 127 if there are more than that many
+conflicts). If the merge was clean, the exit value is 0.
 
 'git merge-file' is designed to be a minimal clone of RCS 'merge'; that is, it
 implements all of RCS 'merge''s functionality which is needed by