Merge "checkout ambiguous ref bugfix" into maint

* commit '0cb6ad3':
  checkout: fix bug with ambiguous refs

builtin/checkout.c

@@ -678,7 +678,7 @@ static const char *unique_tracking_name(const char *name)
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
 	struct checkout_opts opts;
-	unsigned char rev[20];
+	unsigned char rev[20], branch_rev[20];
 	const char *arg;
 	struct branch_info new;
 	struct tree *source_tree = NULL;
@@ -832,18 +832,21 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		argc--;
 
 		new.name = arg;
-		if ((new.commit = lookup_commit_reference_gently(rev, 1))) {
-			setup_branch_path(&new);
+		setup_branch_path(&new);
 
-			if ((check_ref_format(new.path) == CHECK_REF_FORMAT_OK) &&
-			    resolve_ref(new.path, rev, 1, NULL))
-				;
-			else
-				new.path = NULL;
+		if (check_ref_format(new.path) == CHECK_REF_FORMAT_OK &&
+		    resolve_ref(new.path, branch_rev, 1, NULL))
+			hashcpy(rev, branch_rev);
+		else
+			new.path = NULL; /* not an existing branch */
+
+		if (!(new.commit = lookup_commit_reference_gently(rev, 1))) {
+			/* not a commit */
+			source_tree = parse_tree_indirect(rev);
+		} else {
 			parse_commit(new.commit);
 			source_tree = new.commit->tree;
-		} else
-			source_tree = parse_tree_indirect(rev);
+		}
 
 		if (!source_tree)                   /* case (1): want a tree */
 			die("reference is not a tree: %s", arg);

t/t2019-checkout-ambiguous-ref.sh

@@ -0,0 +1,59 @@
+#!/bin/sh
+
+test_description='checkout handling of ambiguous (branch/tag) refs'
+. ./test-lib.sh
+
+test_expect_success 'setup ambiguous refs' '
+	test_commit branch file &&
+	git branch ambiguity &&
+	git branch vagueness &&
+	test_commit tag file &&
+	git tag ambiguity &&
+	git tag vagueness HEAD:file &&
+	test_commit other file
+'
+
+test_expect_success 'checkout ambiguous ref succeeds' '
+	git checkout ambiguity >stdout 2>stderr
+'
+
+test_expect_success 'checkout produces ambiguity warning' '
+	grep "warning.*ambiguous" stderr
+'
+
+test_expect_success 'checkout chooses branch over tag' '
+	echo refs/heads/ambiguity >expect &&
+	git symbolic-ref HEAD >actual &&
+	test_cmp expect actual &&
+	echo branch >expect &&
+	test_cmp expect file
+'
+
+test_expect_success 'checkout reports switch to branch' '
+	grep "Switched to branch" stderr &&
+	! grep "^HEAD is now at" stderr
+'
+
+test_expect_success 'checkout vague ref succeeds' '
+	git checkout vagueness >stdout 2>stderr &&
+	test_set_prereq VAGUENESS_SUCCESS
+'
+
+test_expect_success VAGUENESS_SUCCESS 'checkout produces ambiguity warning' '
+	grep "warning.*ambiguous" stderr
+'
+
+test_expect_success VAGUENESS_SUCCESS 'checkout chooses branch over tag' '
+	echo refs/heads/vagueness >expect &&
+	git symbolic-ref HEAD >actual &&
+	test_cmp expect actual &&
+	echo branch >expect &&
+	test_cmp expect file
+'
+
+test_expect_success VAGUENESS_SUCCESS 'checkout reports switch to branch' '
+	grep "Switched to branch" stderr &&
+	! grep "^HEAD is now at" stderr
+'
+
+test_done