Rollup merge of #64066 - petrochenkov:softstab, r=matthewjasper

Support "soft" feature-gating using a lint

Use it for feature-gating `#[bench]`.

Closes https://github.com/rust-lang/rust/issues/63798.

2 files changed, 17 insertions, 0 deletions

diff --git a/src/test/ui/feature-gates/bench.rs b/src/test/ui/feature-gates/bench.rs
new file mode 100644
index 00000000000..afe4dc7d54c
--- /dev/null
+++ b/src/test/ui/feature-gates/bench.rs
@@ -0,0 +1,5 @@
+#[bench] //~ ERROR use of unstable library feature 'test'
+         //~| WARN this was previously accepted
+fn bench() {}
+
+fn main() {}
diff --git a/src/test/ui/feature-gates/bench.stderr b/src/test/ui/feature-gates/bench.stderr
new file mode 100644
index 00000000000..b9e24e931d4
--- /dev/null
+++ b/src/test/ui/feature-gates/bench.stderr
@@ -0,0 +1,12 @@
+error: use of unstable library feature 'test': `bench` is a part of custom test frameworks which are unstable
+  --> $DIR/bench.rs:1:3
+   |
+LL | #[bench]
+   |   ^^^^^
+   |
+   = note: `#[deny(soft_unstable)]` on by default
+   = 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>
+
+error: aborting due to previous error
+