Add tests for a new feature 'tool_attributes'

src/test/ui/feature-gate-tool_attributes.rs

@@ -0,0 +1,15 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    #[rustfmt::skip] //~ ERROR scoped attribute `rustfmt::skip` is experimental
+    let x = 3
+        ;
+}

src/test/ui/feature-gate-tool_attributes.stderr

@@ -0,0 +1,10 @@
+error[E0658]: scoped attribute `rustfmt::skip` is experimental (see issue #44690)
+  --> $DIR/feature-gate-tool_attributes.rs:12:5
+   |
+12 |     #[rustfmt::skip] //~ ERROR scoped attribute `rustfmt::skip` is experimental
+   |     ^^^^^^^^^^^^^^^^
+   |
+   = help: add #![feature(tool_attributes)] to the crate attributes to enable
+
+error: aborting due to previous error
+