Auto merge of #51363 - japaric:stable-used, r=cramertj

stabilize #[used]

closes #40289

RFC for stabilization: rust-lang/rfcs#2386

r? @Centril

Where should this be documented? Currently the documentation is in the unstable book

src/test/run-make-fulldeps/used/used.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![crate_type = "lib"]
-#![feature(used)]
 
 #[used]
 static FOO: u32 = 0;

src/test/ui/feature-gates/feature-gate-linker-flavor.rs

@@ -1,4 +1,4 @@
-// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// 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.
 //
@@ -15,6 +15,5 @@
 
 #[used]
 fn foo() {}
-//~^^ ERROR the `#[used]` attribute is an experimental feature
 
 fn main() {}

src/test/ui/feature-gates/feature-gate-linker-flavor.stderr

@@ -1,11 +1,8 @@
-error[E0658]: the `#[used]` attribute is an experimental feature (see issue #40289)
+error: attribute must be applied to a `static` variable
   --> $DIR/feature-gate-linker-flavor.rs:16:1
    |
 LL | #[used]
    | ^^^^^^^
-   |
-   = help: add #![feature(used)] to the crate attributes to enable
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0658`.

src/test/ui/feature-gates/feature-gate-used.rs

@@ -1,15 +0,0 @@
-// Copyright 2017 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.
-
-#[used]
-fn foo() {}
-//~^^ ERROR the `#[used]` attribute is an experimental feature
-
-fn main() {}

src/test/ui/feature-gates/feature-gate-used.stderr

@@ -1,11 +0,0 @@
-error[E0658]: the `#[used]` attribute is an experimental feature (see issue #40289)
-  --> $DIR/feature-gate-used.rs:11:1
-   |
-LL | #[used]
-   | ^^^^^^^
-   |
-   = help: add #![feature(used)] to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.

src/test/ui/run-pass/issues/issue-41628.rs

@@ -10,7 +10,6 @@
 
 // run-pass
 #![deny(dead_code)]
-#![feature(used)]
 
 #[used]
 static FOO: u32 = 0;

src/test/ui/used.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(used)]
-
 #[used]
 static FOO: u32 = 0; // OK
 

src/test/ui/used.stderr

@@ -1,23 +1,23 @@
 error: attribute must be applied to a `static` variable
-  --> $DIR/used.rs:16:1
+  --> $DIR/used.rs:14:1
    |
 LL | #[used] //~ ERROR attribute must be applied to a `static` variable
    | ^^^^^^^
 
 error: attribute must be applied to a `static` variable
-  --> $DIR/used.rs:19:1
+  --> $DIR/used.rs:17:1
    |
 LL | #[used] //~ ERROR attribute must be applied to a `static` variable
    | ^^^^^^^
 
 error: attribute must be applied to a `static` variable
-  --> $DIR/used.rs:22:1
+  --> $DIR/used.rs:20:1
    |
 LL | #[used] //~ ERROR attribute must be applied to a `static` variable
    | ^^^^^^^
 
 error: attribute must be applied to a `static` variable
-  --> $DIR/used.rs:25:1
+  --> $DIR/used.rs:23:1
    |
 LL | #[used] //~ ERROR attribute must be applied to a `static` variable
    | ^^^^^^^