Add tests checking that a number of feature gates are gating their features.

Namely:

 * `box_syntax`
 * `box_patterns`
 * `simd_ffi`
 * `macro_reexport`

 cc #22820

src/test/compile-fail-fulldeps/gated-macro-reexports.rs

@@ -0,0 +1,22 @@
+// Copyright 2014 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.
+
+// Test that macro reexports item are gated by `macro_reexport` feature gate.
+
+// aux-build:macro_reexport_1.rs
+// ignore-stage1
+
+#![crate_type = "dylib"]
+
+#[macro_reexport(reexported)]
+#[macro_use] #[no_link]
+extern crate macro_reexport_1;
+//~^ ERROR macros reexports are experimental and possibly buggy
+//~| HELP add #![feature(macro_reexport)] to the crate attributes to enable

src/test/compile-fail/gated-box-patterns.rs

@@ -0,0 +1,22 @@
+// Copyright 2015 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.
+
+// Test that patterns including the box syntax are gated by `box_patterns` feature gate.
+
+fn main() {
+    let x = Box::new(1);
+
+    match x {
+        box 1 => (),
+        //~^ box pattern syntax is experimental
+        //~| add #![feature(box_patterns)] to the crate attributes to enable
+        _     => ()
+    };
+}

src/test/compile-fail/gated-box-syntax.rs

@@ -0,0 +1,17 @@
+// Copyright 2015 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.
+
+// Test that the use of the box syntax is gated by `box_syntax` feature gate.
+
+fn main() {
+    let x = box 3;
+    //~^ ERROR box expression syntax is experimental; you can call `Box::new` instead.
+    //~| HELP add #![feature(box_syntax)] to the crate attributes to enable
+}

src/test/compile-fail/gated-simd-ffi.rs

@@ -0,0 +1,27 @@
+// Copyright 2015 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.
+
+// Test that the use of smid types in the ffi is gated by `smid_ffi` feature gate.
+
+#![feature(simd)]
+
+#[repr(C)]
+#[derive(Copy)]
+#[simd]
+pub struct f32x4(f32, f32, f32, f32);
+
+#[allow(dead_code)]
+extern {
+    fn foo(x: f32x4);
+    //~^ ERROR use of SIMD type `f32x4` in FFI is highly experimental and may result in invalid code
+    //~| HELP add #![feature(simd_ffi)] to the crate attributes to enable
+}
+
+fn main() {}