describe: Avoid unnecessary warning when using --all

In 212945d ("Teach git-describe to verify annotated tag names
before output") git-describe learned how to output a warning if
an annotated tag object was matched but its internal name doesn't
match the local ref name.

However, "git describe --all" causes the local ref name to be
prefixed with "tags/", so we need to skip over this prefix before
comparing the local ref name with the name recorded inside of the
tag object.

Patch-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-describe.c

@@ -160,7 +160,7 @@ static void display_name(struct commit_name *n)
 		n->tag = lookup_tag(n->sha1);
 		if (!n->tag || parse_tag(n->tag) || !n->tag->tag)
 			die("annotated tag %s not available", n->path);
-		if (strcmp(n->tag->tag, n->path))
+		if (strcmp(n->tag->tag, all ? n->path + 5 : n->path))
 			warning("tag '%s' is really '%s' here", n->tag->tag, n->path);
 	}
 

t/t6120-describe.sh

@@ -100,6 +100,12 @@ check_describe B --tags HEAD^^2^
 check_describe B-0-* --long HEAD^^2^
 check_describe A-3-* --long HEAD^^2
 
+: >err.expect
+check_describe A --all A^0
+test_expect_success 'no warning was displayed for A' '
+	test_cmp err.expect err.actual
+'
+
 test_expect_success 'rename tag A to Q locally' '
 	mv .git/refs/tags/A .git/refs/tags/Q
 '