From 0bc458902020b705fa913ca340aa40fea0f87096 Mon Sep 17 00:00:00 2001
From: Junio C Hamano <junkio@cox.net>
Date: Sun, 2 Oct 2005 21:40:51 -0700
Subject: [PATCH] Make sure get_sha1 does not accept ambiguous sha1 prefix
 (again).

The earlier fix incorrectly dropped the code the original had to
ensure the found SHA1 is at least unique within the same pack.
Restore the check.

Signed-off-by: Junio C Hamano <junkio@cox.net>
---
 sha1_name.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/sha1_name.c b/sha1_name.c
index 8920de1c45..f64755fbce 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -91,14 +91,23 @@ static int find_short_packed_object(int len, const unsigned char *match, unsigne
 			last = mid;
 		}
 		if (first < num) {
-			unsigned char now[20];
+			unsigned char now[20], next[20];
 			nth_packed_object_sha1(p, first, now);
 			if (match_sha(len, match, now)) {
-				if (!found) {
-					memcpy(found_sha1, now, 20);
-					found++;
+				if (nth_packed_object_sha1(p, first+1, next) ||
+				    !match_sha(len, match, next)) {
+					/* unique within this pack */
+					if (!found) {
+						memcpy(found_sha1, now, 20);
+						found++;
+					}
+					else if (memcmp(found_sha1, now, 20)) {
+						found = 2;
+						break;
+					}
 				}
-				else if (memcmp(found_sha1, now, 20)) {
+				else {
+					/* not even unique within this pack */
 					found = 2;
 					break;
 				}
@@ -121,7 +130,7 @@ static int find_unique_short_object(int len, char *canonical,
 	if (!has_unpacked && !has_packed)
 		return -1;
 	if (1 < has_unpacked || 1 < has_packed)
-		return -1;
+		return error("short SHA1 %.*s is ambiguous.", len, canonical);
 	if (has_unpacked != has_packed) {
 		memcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1), 20);
 		return 0;