Make sure heads/foo and tags/foo do not confuse things.

When both heads/foo and tags/foo exist, get_sha1_basic("foo")
picked up the tag without complaining, which is quite confusing.
Make sure we require unambiguous form, "heads/foo" or "tags/foo"
in such cases.

Signed-off-by: Junio C Hamano <junkio@cox.net>

2 files changed, 24 insertions, 6 deletions

diff --git a/sha1_name.c b/sha1_name.c
index be1755a70b..faac158b16 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -236,6 +236,7 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		NULL
 	};
 	const char **p;
+	int found = 0;
 
 	if (len == 40 && !get_sha1_hex(str, sha1))
 		return 0;
@@ -246,10 +247,20 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 
 	for (p = prefix; *p; p++) {
 		char *pathname = git_path("%s/%.*s", *p, len, str);
-		if (!read_ref(pathname, sha1))
-			return 0;
+		if (!read_ref(pathname, sha1)) {
+			/* Must be unique; i.e. when heads/foo and
+			 * tags/foo are both present, reject "foo".
+			 * Note that read_ref() eventually calls
+			 * get_sha1_hex() which can smudge initial
+			 * part of the buffer even if what is read
+			 * is found to be invalid halfway.
+			 */
+			if (1 < found++)
+				return -1;
+		}
 	}
-
+	if (found == 1)
+		return 0;
 	return -1;
 }
 
diff --git a/show-branch.c b/show-branch.c
index 631336cd9d..d8808eefce 100644
--- a/show-branch.c
+++ b/show-branch.c
@@ -313,9 +313,16 @@ static int append_ref(const char *refname, const unsigned char *sha1)
 
 static int append_head_ref(const char *refname, const unsigned char *sha1)
 {
-	if (strncmp(refname, "refs/heads/", 11))
+	unsigned char tmp[20];
+	int ofs = 11;
+	if (strncmp(refname, "refs/heads/", ofs))
 		return 0;
-	return append_ref(refname + 11, sha1);
+	/* If both heads/foo and tags/foo exists, get_sha1 would
+	 * get confused.
+	 */
+	if (get_sha1(refname + ofs, tmp) || memcmp(tmp, sha1, 20))
+		ofs = 5;
+	return append_ref(refname + ofs, sha1);
 }
 
 static int append_tag_ref(const char *refname, const unsigned char *sha1)
@@ -470,7 +477,7 @@ int main(int ac, char **av)
 		if (MAX_REVS <= num_rev)
 			die("cannot handle more than %d revs.", MAX_REVS);
 		if (get_sha1(ref_name[num_rev], revkey))
-			usage(show_branch_usage);
+			die("'%s' is not a valid ref.\n", ref_name[num_rev]);
 		commit = lookup_commit_reference(revkey);
 		if (!commit)
 			die("cannot find commit %s (%s)",