builtin builtin: Print help if run without an action to do

Fixes #9942

fish-rust/src/builtins/builtin.rs

@@ -56,6 +56,14 @@ pub fn r#builtin(
         return STATUS_INVALID_ARGS;
     }
 
+    // If we don't have either, we print our help.
+    // This is also what e.g. command and time,
+    // the other decorator/builtins do.
+    if !opts.query && !opts.list_names {
+        builtin_print_help(parser, streams, cmd);
+        return STATUS_INVALID_ARGS;
+    }
+
     if opts.query {
         let optind = w.woptind;
         for arg in argv.iter().take(argc).skip(optind) {

tests/checks/builtinbuiltin.fish

@@ -9,4 +9,9 @@ builtin -nq string
 #CHECKERR: builtin: invalid option combination, --query and --names are mutually exclusive
 echo $status
 #CHECK: 2
+
+builtin -- -q &| grep -q "builtin - run a builtin command\|fish: builtin: missing man page"
+echo $status
+#CHECK: 0
+
 exit 0