remote: use remote_is_configured() for add and rename

Both remote add and remote rename use a slightly different hand-rolled
check if the remote exits.  The hand-rolled check may have some subtle
cases in which it might fail to detect when a remote already exists.
One such case was fixed in fb86e32 ("git remote: allow adding remotes
agreeing with url.<...>.insteadOf").  Another case is when a remote is
configured as follows:

  [remote "foo"]
    vcs = bar

If we try to run `git remote add foo bar` with the above remote
configuration, git segfaults.  This change fixes it.

In addition, git remote rename $existing foo with the configuration for
foo as above silently succeeds, even though foo already exists,
modifying its configuration.  With this patch it fails with "remote foo
already exists".

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/remote.c

@@ -186,10 +186,7 @@ static int add(int argc, const char **argv)
 	url = argv[1];
 
 	remote = remote_get(name);
-	if (remote && (remote->url_nr > 1 ||
-			(strcmp(name, remote->url[0]) &&
-				strcmp(url, remote->url[0])) ||
-			remote->fetch_refspec_nr))
+	if (remote_is_configured(remote))
 		die(_("remote %s already exists."), name);
 
 	strbuf_addf(&buf2, "refs/heads/test:refs/remotes/%s/test", name);
@@ -641,7 +638,7 @@ static int mv(int argc, const char **argv)
 		return migrate_file(oldremote);
 
 	newremote = remote_get(rename.new);
-	if (newremote && (newremote->url_nr > 1 || newremote->fetch_refspec_nr))
+	if (remote_is_configured(newremote))
 		die(_("remote %s already exists."), rename.new);
 
 	strbuf_addf(&buf, "refs/heads/test:refs/remotes/%s/test", rename.new);

t/t5505-remote.sh

@@ -157,6 +157,21 @@ test_expect_success 'rename errors out early when deleting non-existent branch'
 	)
 '
 
+test_expect_success 'add existing foreign_vcs remote' '
+	test_config remote.foo.vcs bar &&
+	echo "fatal: remote foo already exists." >expect &&
+	test_must_fail git remote add foo bar 2>actual &&
+	test_i18ncmp expect actual
+'
+
+test_expect_success 'add existing foreign_vcs remote' '
+	test_config remote.foo.vcs bar &&
+	test_config remote.bar.vcs bar &&
+	echo "fatal: remote bar already exists." >expect &&
+	test_must_fail git remote rename foo bar 2>actual &&
+	test_i18ncmp expect actual
+'
+
 cat >test/expect <<EOF
 * remote origin
   Fetch URL: $(pwd)/one