Teach @{-1} to git merge

1.6.2 will have @{-1} syntax advertised as "usable anywhere you can use
a branch name".  However, "git merge @{-1}" did not work.

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

builtin-merge.c

@@ -356,9 +356,14 @@ static void merge_name(const char *remote, struct strbuf *msg)
 	struct object *remote_head;
 	unsigned char branch_head[20], buf_sha[20];
 	struct strbuf buf = STRBUF_INIT;
+	struct strbuf bname = STRBUF_INIT;
 	const char *ptr;
 	int len, early;
 
+	len = strlen(remote);
+	if (interpret_nth_last_branch(remote, &bname) == len)
+		remote = bname.buf;
+
 	memset(branch_head, 0, sizeof(branch_head));
 	remote_head = peel_to_type(remote, 0, NULL, OBJ_COMMIT);
 	if (!remote_head)
@@ -371,7 +376,7 @@ static void merge_name(const char *remote, struct strbuf *msg)
 	if (!hashcmp(remote_head->sha1, branch_head)) {
 		strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 			sha1_to_hex(branch_head), remote);
-		return;
+		goto cleanup;
 	}
 
 	/* See if remote matches <name>^^^.. or <name>~<number> */
@@ -411,7 +416,8 @@ static void merge_name(const char *remote, struct strbuf *msg)
 				    sha1_to_hex(remote_head->sha1),
 				    truname.buf + 11,
 				    (early ? " (early part)" : ""));
-			return;
+			strbuf_release(&truname);
+			goto cleanup;
 		}
 	}
 
@@ -432,10 +438,13 @@ static void merge_name(const char *remote, struct strbuf *msg)
 			strbuf_remove(&line, ptr-line.buf+1, 13);
 		strbuf_addbuf(msg, &line);
 		strbuf_release(&line);
-		return;
+		goto cleanup;
 	}
 	strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 		sha1_to_hex(remote_head->sha1), remote);
+cleanup:
+	strbuf_release(&buf);
+	strbuf_release(&bname);
 }
 
 static int git_merge_config(const char *k, const char *v, void *cb)

t/t0100-previous.sh

@@ -22,5 +22,28 @@ test_expect_success 'branch -d @{-12} when there is not enough switches yet' '
 	git rev-parse --verify refs/heads/master
 '
 
+test_expect_success 'merge @{-1}' '
+	git checkout A &&
+	test_commit B &&
+	git checkout A &&
+	test_commit C &&
+	git branch -f master B &&
+	git branch -f other &&
+	git checkout other &&
+	git checkout master &&
+	git merge @{-1} &&
+	git cat-file commit HEAD | grep "Merge branch '\''other'\''"
+'
+
+test_expect_success 'merge @{-1} when there is not enough switches yet' '
+	git reflog expire --expire=now &&
+	git checkout -f master &&
+	git reset --hard B &&
+	git branch -f other C &&
+	git checkout other &&
+	git checkout master &&
+	test_must_fail git merge @{-12}
+'
+
 test_done