diffcore-break: don't divide by zero

When the source file is empty, the calculation of the merge score
results in a division by zero.  In the situation:

== preimage ==             == postimage ==

F (empty file)             F (a large file)
E (a new empty file)

it does not make sense to consider F->E as a rename, so it is better not
to break the pre- and post-image of F.

Bail out early in this case to avoid hitting the divide-by-zero.  This
causes the merge score to be left at zero.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diffcore-break.c b/diffcore-break.c
index 44f8678d22ea466b0867591429bbcc3285cdaf91..1d9e530a84758e34d616690684c4842cd1af4cfc 100644 (file)
--- a/diffcore-break.c
+++ b/diffcore-break.c
@@ -68,6 +68,9 @@ static int should_break(struct diff_filespec *src,
        if (max_size < MINIMUM_BREAK_SIZE)
                return 0; /* we do not break too small filepair */
 
+       if (!src->size)
+               return 0; /* we do not let empty files get renamed */
+
        if (diffcore_count_changes(src, dst,
                                   &src->cnt_data, &dst->cnt_data,
                                   0,