de-stabilize bench attribute

Author: RalfJung

library/core/src/macros/mod.rs

@@ -1683,7 +1683,6 @@ pub(crate) mod builtin {
     #[unstable(
         feature = "test",
         issue = "50297",
-        soft,
         reason = "`bench` is a part of custom test frameworks which are unstable"
     )]
     #[allow_internal_unstable(test, rustc_attrs, coverage_attribute)]

tests/ui/feature-gates/bench.rs

@@ -1,9 +1,7 @@
 //@ edition:2018
 
 #[bench] //~ ERROR use of unstable library feature `test`
-         //~| WARN this was previously accepted
 fn bench() {}
 
 use bench as _; //~ ERROR use of unstable library feature `test`
-                //~| WARN this was previously accepted
 fn main() {}

tests/ui/feature-gates/bench.stderr

@@ -1,43 +1,23 @@
-error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
+error[E0658]: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
   --> $DIR/bench.rs:3:3
    |
 LL | #[bench]
    |   ^^^^^
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
-   = note: `#[deny(soft_unstable)]` on by default
+   = note: see issue #50297 <https://github.com/rust-lang/rust/issues/50297> for more information
+   = help: add `#![feature(test)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
-  --> $DIR/bench.rs:7:5
+error[E0658]: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
+  --> $DIR/bench.rs:6:5
    |
 LL | use bench as _;
    |     ^^^^^
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
+   = note: see issue #50297 <https://github.com/rust-lang/rust/issues/50297> for more information
+   = help: add `#![feature(test)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error: aborting due to 2 previous errors
 
-Future incompatibility report: Future breakage diagnostic:
-error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
-  --> $DIR/bench.rs:3:3
-   |
-LL | #[bench]
-   |   ^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
-   = note: `#[deny(soft_unstable)]` on by default
-
-Future breakage diagnostic:
-error: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
-  --> $DIR/bench.rs:7:5
-   |
-LL | use bench as _;
-   |     ^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
-   = note: `#[deny(soft_unstable)]` on by default
-
+For more information about this error, try `rustc --explain E0658`.

tests/ui/lint/expansion-time.rs

@@ -9,13 +9,6 @@ macro_rules! foo {
 macro_rules! m { ($i) => {} } //~ WARN missing fragment specifier
                               //~| WARN this was previously accepted
 
-#[warn(soft_unstable)]
-mod benches {
-    #[bench] //~ WARN use of unstable library feature `test`
-             //~| WARN this was previously accepted
-    fn foo() {}
-}
-
 #[deprecated = "reason"]
 macro_rules! deprecated {
     () => {}

tests/ui/lint/expansion-time.stderr

@@ -26,33 +26,19 @@ note: the lint level is defined here
 LL | #[warn(missing_fragment_specifier)]
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
-  --> $DIR/expansion-time.rs:14:7
-   |
-LL |     #[bench]
-   |       ^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
-note: the lint level is defined here
-  --> $DIR/expansion-time.rs:12:8
-   |
-LL | #[warn(soft_unstable)]
-   |        ^^^^^^^^^^^^^
-
 warning: include macro expected single expression in source
   --> $DIR/expansion-time-include.rs:4:1
    |
 LL | 2
    | ^
    |
 note: the lint level is defined here
-  --> $DIR/expansion-time.rs:29:8
+  --> $DIR/expansion-time.rs:22:8
    |
 LL | #[warn(incomplete_include)]
    |        ^^^^^^^^^^^^^^^^^^
 
-warning: 4 warnings emitted
+warning: 3 warnings emitted
 
 Future incompatibility report: Future breakage diagnostic:
 warning: missing fragment specifier
@@ -69,18 +55,3 @@ note: the lint level is defined here
 LL | #[warn(missing_fragment_specifier)]
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Future breakage diagnostic:
-warning: use of unstable library feature `test`: `bench` is a part of custom test frameworks which are unstable
-  --> $DIR/expansion-time.rs:14:7
-   |
-LL |     #[bench]
-   |       ^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
-note: the lint level is defined here
-  --> $DIR/expansion-time.rs:12:8
-   |
-LL | #[warn(soft_unstable)]
-   |        ^^^^^^^^^^^^^
-