Rollup merge of #145251 - tiif:support_trait, r=BoxyUwU

Support using #[unstable_feature_bound] on trait

This is needed to unblock https://github.com/rust-lang/rust/pull/145095

r? ```````@BoxyUwU```````

4 files changed, 57 insertions, 6 deletions

diff --git a/tests/ui/unstable-feature-bound/unstable_feature_bound_on_trait.fail.stderr b/tests/ui/unstable-feature-bound/unstable_feature_bound_on_trait.fail.stderr
new file mode 100644
index 00000000000..69be101a40d
--- /dev/null
+++ b/tests/ui/unstable-feature-bound/unstable_feature_bound_on_trait.fail.stderr
@@ -0,0 +1,18 @@
+error: unstable feature `foo` is used without being enabled.
+  --> $DIR/unstable_feature_bound_on_trait.rs:28:5
+   |
+LL |     Foo::bar();
+   |     ^^^^^^^^^^
+   |
+   = help: The feature can be enabled by marking the current item with `#[unstable_feature_bound(foo)]`
+note: required by a bound in `Bar::bar`
+  --> $DIR/unstable_feature_bound_on_trait.rs:16:1
+   |
+LL | #[unstable_feature_bound(foo)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Bar::bar`
+...
+LL |     fn bar() {}
+   |        --- required by a bound in this associated function
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/unstable-feature-bound/unstable_feature_bound_on_trait.rs b/tests/ui/unstable-feature-bound/unstable_feature_bound_on_trait.rs
new file mode 100644
index 00000000000..0ee00d5e7fb
--- /dev/null
+++ b/tests/ui/unstable-feature-bound/unstable_feature_bound_on_trait.rs
@@ -0,0 +1,33 @@
+//@ revisions: pass fail
+//@[pass] check-pass
+
+#![allow(internal_features)]
+#![feature(staged_api)]
+#![stable(feature = "a", since = "1.1.1" )]
+
+/// Test the behaviour of marking a trait with #[unstable_feature_bound].
+/// In this testcase, even though the trait method `bar` and the `struct Foo` are
+/// both stable, #[unstable_feature_bound] is still needed at the call site of Foo::bar().
+
+#[stable(feature = "a", since = "1.1.1" )]
+struct Foo;
+
+#[unstable(feature = "foo", issue = "none" )]
+#[unstable_feature_bound(foo)]
+trait Bar {
+    #[stable(feature = "a", since = "1.1.1" )]
+    fn bar() {}
+}
+
+#[unstable_feature_bound(foo)]
+impl Bar for Foo {
+}
+
+#[cfg_attr(pass, unstable_feature_bound(foo))]
+fn moo() {
+    Foo::bar();
+    //[fail]~^ ERROR: unstable feature `foo` is used without being enabled.
+}
+
+
+fn main() {}
diff --git a/tests/ui/unstable-feature-bound/unstable_inherent_method.rs b/tests/ui/unstable-feature-bound/unstable_inherent_method.rs
index 5f3095430a8..0d6e4ebb408 100644
--- a/tests/ui/unstable-feature-bound/unstable_inherent_method.rs
+++ b/tests/ui/unstable-feature-bound/unstable_inherent_method.rs
@@ -9,14 +9,14 @@
 pub trait Trait {
     #[unstable(feature = "feat", issue = "none" )]
     #[unstable_feature_bound(foo)]
-    //~^ ERROR: attribute should be applied to `impl` or free function outside of any `impl` or trait
+    //~^ ERROR: attribute should be applied to `impl`, trait or free function
     fn foo();
 }
 
 #[stable(feature = "a", since = "1.1.1" )]
 impl Trait for u8 {
     #[unstable_feature_bound(foo)]
-    //~^ ERROR: attribute should be applied to `impl` or free function outside of any `impl` or trait
+    //~^ ERROR: attribute should be applied to `impl`, trait or free function
     fn foo() {}
 }
 
diff --git a/tests/ui/unstable-feature-bound/unstable_inherent_method.stderr b/tests/ui/unstable-feature-bound/unstable_inherent_method.stderr
index fa1c39db259..90cbb32df7c 100644
--- a/tests/ui/unstable-feature-bound/unstable_inherent_method.stderr
+++ b/tests/ui/unstable-feature-bound/unstable_inherent_method.stderr
@@ -1,20 +1,20 @@
-error: attribute should be applied to `impl` or free function outside of any `impl` or trait
+error: attribute should be applied to `impl`, trait or free function
   --> $DIR/unstable_inherent_method.rs:11:5
    |
 LL |     #[unstable_feature_bound(foo)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL |     fn foo();
-   |     --------- not an `impl` or free function
+   |     --------- not an `impl`, trait or free function
 
-error: attribute should be applied to `impl` or free function outside of any `impl` or trait
+error: attribute should be applied to `impl`, trait or free function
   --> $DIR/unstable_inherent_method.rs:18:5
    |
 LL |     #[unstable_feature_bound(foo)]
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |
 LL |     fn foo() {}
-   |     ----------- not an `impl` or free function
+   |     ----------- not an `impl`, trait or free function
 
 error: aborting due to 2 previous errors