Stabilize the #[global_allocator] attribute

Fixes https://github.com/rust-lang/rust/issues/27389

src/libsyntax/feature_gate.rs

@@ -357,8 +357,6 @@ declare_features! (
     // Trait aliases
     (active, trait_alias, "1.24.0", Some(41517), None),
 
-    // global allocators and their internals
-    (active, global_allocator, "1.20.0", Some(27389), None),
     // rustc internal
     (active, allocator_internals, "1.20.0", None, None),
 
@@ -615,6 +613,8 @@ declare_features! (
     (accepted, macro_lifetime_matcher, "1.27.0", Some(34303), None),
     // Termination trait in tests (RFC 1937)
     (accepted, termination_trait_test, "1.27.0", Some(48854), None),
+    // The #[global_allocator] attribute
+    (accepted, global_allocator, "1.28.0", Some(27389), None),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -776,11 +776,7 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                              "the `#[rustc_const_unstable]` attribute \
                                               is an internal feature",
                                              cfg_fn!(rustc_const_unstable))),
-    ("global_allocator", Normal, Gated(Stability::Unstable,
-                                       "global_allocator",
-                                       "the `#[global_allocator]` attribute is \
-                                        an experimental feature",
-                                       cfg_fn!(global_allocator))),
+    ("global_allocator", Normal, Ungated),
     ("default_lib_allocator", Whitelisted, Gated(Stability::Unstable,
                                             "allocator_internals",
                                             "the `#[default_lib_allocator]` \

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

@@ -1,14 +0,0 @@
-// Copyright 2016 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.
-
-#[global_allocator] //~ ERROR: attribute is an experimental feature
-static A: usize = 0;
-
-fn main() {}

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

@@ -1,11 +0,0 @@
-error[E0658]: the `#[global_allocator]` attribute is an experimental feature (see issue #27389)
-  --> $DIR/feature-gate-global_allocator.rs:11:1
-   |
-LL | #[global_allocator] //~ ERROR: attribute is an experimental feature
-   | ^^^^^^^^^^^^^^^^^^^
-   |
-   = help: add #![feature(global_allocator)] to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.