Warn use of "origin" when remotes/origin/HEAD is dangling

The previous one squelched the diagnositic message we used to issue every
time we enumerated the refs and noticed a dangling ref.  This adds the
warning back to the place where the user actually attempts to use it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_name.c

@@ -268,16 +268,18 @@ int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 		char fullref[PATH_MAX];
 		unsigned char sha1_from_ref[20];
 		unsigned char *this_result;
+		int flag;
 
 		this_result = refs_found ? sha1_from_ref : sha1;
 		mksnpath(fullref, sizeof(fullref), *p, len, str);
-		r = resolve_ref(fullref, this_result, 1, NULL);
+		r = resolve_ref(fullref, this_result, 1, &flag);
 		if (r) {
 			if (!refs_found++)
 				*ref = xstrdup(r);
 			if (!warn_ambiguous_refs)
 				break;
-		}
+		} else if (flag & REF_ISSYMREF)
+			warning("ignoring dangling symref %s.", fullref);
 	}
 	free(last_branch);
 	return refs_found;

t/t5505-remote.sh

@@ -421,6 +421,12 @@ test_expect_success 'remote prune to cause a dangling symref' '
 		git branch -a
 	) 2>err &&
 	! grep "points nowhere" err
+	(
+		cd seven &&
+		test_must_fail git branch nomore origin
+	) 2>err &&
+	grep "dangling symref" err
 '
 
 test_done
+