remote: actually check if remote exits

When converting the git remote command to a builtin in 211c89 ("Make
git-remote a builtin"), a few calls to check if a remote exists were
converted from:
       if (!exists $remote->{$name}) {
       	  [...]
to:
       remote = remote_get(argv[1]);
       if (!remote)
          [...]

The new check is not quite correct, because remote_get() never returns
NULL if a name is given.  This leaves us with the somewhat cryptic error
message "error: Could not remove config section 'remote.test'", if we
are trying to remove a remote that does not exist, or a similar error if
we try to rename a remote.

Use the remote_is_configured() function to check whether the remote
actually exists, and die with a more sensible error message ("No such
remote: $remotename") instead if it doesn't.

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

@@ -634,7 +634,7 @@ static int mv(int argc, const char **argv)
 	rename.remote_branches = &remote_branches;
 
 	oldremote = remote_get(rename.old);
-	if (!oldremote)
+	if (!remote_is_configured(oldremote))
 		die(_("No such remote: %s"), rename.old);
 
 	if (!strcmp(rename.old, rename.new) && oldremote->origin != REMOTE_CONFIG)
@@ -773,7 +773,7 @@ static int rm(int argc, const char **argv)
 		usage_with_options(builtin_remote_rm_usage, options);
 
 	remote = remote_get(argv[1]);
-	if (!remote)
+	if (!remote_is_configured(remote))
 		die(_("No such remote: %s"), argv[1]);
 
 	known_remotes.to_delete = remote;

t/t5505-remote.sh

@@ -139,6 +139,24 @@ test_expect_success 'remove remote protects local branches' '
 	)
 '
 
+test_expect_success 'remove errors out early when deleting non-existent branch' '
+	(
+		cd test &&
+		echo "fatal: No such remote: foo" >expect &&
+		test_must_fail git remote rm foo 2>actual &&
+		test_i18ncmp expect actual
+	)
+'
+
+test_expect_success 'rename errors out early when deleting non-existent branch' '
+	(
+		cd test &&
+		echo "fatal: No such remote: foo" >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