Fix TAIT & ATPIT feature gating in the presence of anon consts

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -99,6 +99,13 @@ impl<'a> PostExpansionVisitor<'a> {
                 }
                 visit::walk_ty(self, ty);
             }
+
+            fn visit_anon_const(&mut self, _: &ast::AnonConst) -> Self::Result {
+                // We don't walk the anon const because it crosses a conceptual boundary: We're no
+                // longer "inside" the original type.
+                // Brittle: We assume that the callers of `check_impl_trait` will later recurse into
+                // the items found in the AnonConst to look for nested TyAliases.
+            }
         }
         ImplTraitVisitor { vis: self, in_associated_ty }.visit_ty(ty);
     }

tests/ui/feature-gates/feature-gate-impl_trait_in_assoc_type.rs

@@ -17,4 +17,13 @@ impl Mop {
     //~| ERROR: unconstrained opaque type
 }
 
+fn funky(_: [(); {
+    impl Foo for fn() {
+        type Bar = impl Sized;
+        //~^ ERROR: `impl Trait` in associated types is unstable
+        //~| ERROR: unconstrained opaque type
+    }
+    0
+}]) {}
+
 fn main() {}

tests/ui/feature-gates/feature-gate-impl_trait_in_assoc_type.stderr

@@ -18,6 +18,16 @@ LL |     type Bop = impl std::fmt::Debug;
    = help: add `#![feature(impl_trait_in_assoc_type)]` 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    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date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[E0658]: `impl Trait` in associated types is unstable
+  --> $DIR/feature-gate-impl_trait_in_assoc_type.rs:22:20
+   |
+LL |         type Bar = impl Sized;
+   |                    ^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(impl_trait_in_assoc_type)]` 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+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date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[E0658]: inherent associated types are unstable
   --> $DIR/feature-gate-impl_trait_in_assoc_type.rs:14:5
    |
@@ -44,6 +54,14 @@ LL |     type Bop = impl std::fmt::Debug;
    |
    = note: `Bop` must be used in combination with a concrete type within the same impl
 
-error: aborting due to 5 previous errors
+error: unconstrained opaque type
+  --> $DIR/feature-gate-impl_trait_in_assoc_type.rs:22:20
+   |
+LL |         type Bar = impl Sized;
+   |                    ^^^^^^^^^^
+   |
+   = note: `Bar` must be used in combination with a concrete type within the same impl
+
+error: aborting due to 7 previous errors
 
 For more information about this error, try `rustc --explain E0658`.

tests/ui/feature-gates/feature-gate-type_alias_impl_trait.rs

@@ -1,38 +1,42 @@
-//@ check-pass
-#![feature(type_alias_impl_trait)]
 use std::fmt::Debug;
 
-type Foo = impl Debug;
+type Foo = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable
 
 struct Bar(Foo);
-#[define_opaque(Foo)]
+#[define_opaque(Foo)] //~ ERROR use of unstable library feature `type_alias_impl_trait`
 fn define() -> Bar {
     Bar(42)
 }
 
-type Foo2 = impl Debug;
+type Foo2 = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable
 
-#[define_opaque(Foo2)]
+#[define_opaque(Foo2)] //~ ERROR use of unstable library feature `type_alias_impl_trait`
 fn define2() {
     let x = || -> Foo2 { 42 };
 }
 
-type Foo3 = impl Debug;
+type Foo3 = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable
 
-#[define_opaque(Foo3)]
+#[define_opaque(Foo3)] //~ ERROR use of unstable library feature `type_alias_impl_trait`
 fn define3(x: Foo3) {
     let y: i32 = x;
 }
-#[define_opaque(Foo3)]
+#[define_opaque(Foo3)] //~ ERROR use of unstable library feature `type_alias_impl_trait`
 fn define3_1() {
     define3(42)
 }
 
-type Foo4 = impl Debug;
+type Foo4 = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable
 
-#[define_opaque(Foo4)]
+#[define_opaque(Foo4)] //~ ERROR use of unstable library feature `type_alias_impl_trait`
 fn define4(_: Foo4) {
     let y: Foo4 = 42;
 }
 
+type Foo5 = [(); {
+    type Foo = impl Debug; //~ ERROR `impl Trait` in type aliases is unstable
+    //~^ ERROR unconstrained opaque type
+    0
+}];
+
 fn main() {}

tests/ui/feature-gates/feature-gate-type_alias_impl_trait.stderr

@@ -0,0 +1,111 @@
+error[E0658]: use of unstable library feature `type_alias_impl_trait`: `type_alias_impl_trait` has open design concerns
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:6:3
+   |
+LL | #[define_opaque(Foo)]
+   |   ^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: use of unstable library feature `type_alias_impl_trait`: `type_alias_impl_trait` has open design concerns
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:13:3
+   |
+LL | #[define_opaque(Foo2)]
+   |   ^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: use of unstable library feature `type_alias_impl_trait`: `type_alias_impl_trait` has open design concerns
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:20:3
+   |
+LL | #[define_opaque(Foo3)]
+   |   ^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: use of unstable library feature `type_alias_impl_trait`: `type_alias_impl_trait` has open design concerns
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:24:3
+   |
+LL | #[define_opaque(Foo3)]
+   |   ^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: use of unstable library feature `type_alias_impl_trait`: `type_alias_impl_trait` has open design concerns
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:31:3
+   |
+LL | #[define_opaque(Foo4)]
+   |   ^^^^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: `impl Trait` in type aliases is unstable
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:3:12
+   |
+LL | type Foo = impl Debug;
+   |            ^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: `impl Trait` in type aliases is unstable
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:11:13
+   |
+LL | type Foo2 = impl Debug;
+   |             ^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: `impl Trait` in type aliases is unstable
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:18:13
+   |
+LL | type Foo3 = impl Debug;
+   |             ^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: `impl Trait` in type aliases is unstable
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:29:13
+   |
+LL | type Foo4 = impl Debug;
+   |             ^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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[E0658]: `impl Trait` in type aliases is unstable
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:37:16
+   |
+LL |     type Foo = impl Debug;
+   |                ^^^^^^^^^^
+   |
+   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
+   = help: add `#![feature(type_alias_impl_trait)]` 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: unconstrained opaque type
+  --> $DIR/feature-gate-type_alias_impl_trait.rs:37:16
+   |
+LL |     type Foo = impl Debug;
+   |                ^^^^^^^^^^
+   |
+   = note: `Foo` must be used in combination with a concrete type within the same crate
+
+error: aborting due to 11 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/impl-trait/impl_trait_projections.rs

@@ -35,4 +35,9 @@ fn projection_from_impl_trait_inside_dyn_trait_is_disallowed()
     panic!()
 }
 
+fn parametrized_value_in_anon_const_is_disallowed() -> [(); None::<impl Sized>] {
+    //~^ ERROR `impl Trait` is not allowed in paths
+    loop {}
+}
+
 fn main() {}

tests/ui/impl-trait/impl_trait_projections.stderr

@@ -30,6 +30,14 @@ LL |     -> <dyn Iterator<Item = impl Debug> as Iterator>::Item
    |
    = note: `impl Trait` is only allowed in arguments and return types of functions and methods
 
-error: aborting due to 4 previous errors
+error[E0562]: `impl Trait` is not allowed in paths
+  --> $DIR/impl_trait_projections.rs:38:68
+   |
+LL | fn parametrized_value_in_anon_const_is_disallowed() -> [(); None::<impl Sized>] {
+   |                                                                    ^^^^^^^^^^
+   |
+   = note: `impl Trait` is only allowed in arguments and return types of functions and methods
+
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0562`.

tests/ui/impl-trait/inside-item-nested-in-anon-const.rs

@@ -0,0 +1,25 @@
+// Ensure we don't misclassify `impl Trait` as TAIT/ATPIT if located inside an anon const in a
+// type alias/assoc type.
+// issue: <https://github.com/rust-lang/rust/issues/139055>
+//@ check-pass
+#![forbid(unstable_features)]
+
+struct Girder<const N: usize>;
+
+type Alias = Girder<{
+    fn pass(input: impl Sized) -> impl Sized { input }
+    0
+}>;
+
+trait Trait {
+    type Assoc;
+}
+
+impl Trait for () {
+    type Assoc = [(); {
+        fn pass(input: impl Sized) -> impl Sized { input }
+        0
+    }];
+}
+
+fn main() {}