find_unique_abbrev: use 4-buffer ring

Some code paths want to format multiple abbreviated sha1s in
the same output line. Because we use a single static buffer
for our return value, they have to either break their output
into several calls or allocate their own arrays and use
find_unique_abbrev_r().

Intead, let's mimic sha1_to_hex() and use a ring of several
buffers, so that the return value stays valid through
multiple calls. This shortens some of the callers, and makes
it harder to for them to make a silly mistake.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/cache.h b/cache.h
index f7ee414..607fe6e 100644
--- a/cache.h
+++ b/cache.h
@@ -903,8 +903,8 @@ extern char *sha1_pack_index_name(const unsigned char *sha1);
  * The result will be at least `len` characters long, and will be NUL
  * terminated.
  *
- * The non-`_r` version returns a static buffer which will be overwritten by
- * subsequent calls.
+ * The non-`_r` version returns a static buffer which remains valid until 4
+ * more calls to find_unique_abbrev are made.
  *
  * The `_r` variant writes to a buffer supplied by the caller, which must be at
  * least `GIT_SHA1_HEXSZ + 1` bytes. The return value is the number of bytes