diff: Fix rename pretty-print when suffix and prefix overlap

When considering a rename for two files that have a suffix and a prefix
that can overlap, a confusing line is shown. As an example, renaming
"a/b/b/c" to "a/b/c" shows "a/b/{ => }/b/c".

Currently, what we do is calculate the common prefix ("a/b/"), and the
common suffix ("/b/c"), but the same "/b/" is actually counted both in
prefix and suffix. Then when calculating the size of the non-common part,
we end-up with a negative value which is reset to 0, thus the "{ => }".

Do not allow the common suffix to overlap the common prefix and stop
when reaching a "/" that would be in both.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diff.c b/diff.c
index 9038f19..e1d82c9 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -1177,7 +1177,16 @@ static char *pprint_rename(const char *a, const char *b)
        old = a + len_a;
        new = b + len_b;
        sfx_length = 0;
-       while (a <= old && b <= new && *old == *new) {
+       /*
+        * Note:
+        * if pfx_length is 0, old/new will never reach a - 1 because it
+        * would mean the whole string is common suffix. But then, the
+        * whole string would also be a common prefix, and we would not
+        * have pfx_length equals 0.
+        */
+       while (a + pfx_length - 1 <= old &&
+              b + pfx_length - 1 <= new &&
+              *old == *new) {
                if (*old == '/')
                        sfx_length = len_a - (old - a);
                old--;