Split out a separate feature gate for impl trait in associated types

3 files changed, 23 insertions, 10 deletions

diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 007d64f681f..9cbc4b2e2dc 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -121,24 +121,34 @@ impl<'a> PostExpansionVisitor<'a> {
     }
 
     /// Feature gate `impl Trait` inside `type Alias = $type_expr;`.
-    fn check_impl_trait(&self, ty: &ast::Ty) {
+    fn check_impl_trait(&self, ty: &ast::Ty, in_associated_ty: bool) {
         struct ImplTraitVisitor<'a> {
             vis: &'a PostExpansionVisitor<'a>,
+            in_associated_ty: bool,
         }
         impl Visitor<'_> for ImplTraitVisitor<'_> {
             fn visit_ty(&mut self, ty: &ast::Ty) {
                 if let ast::TyKind::ImplTrait(..) = ty.kind {
-                    gate_feature_post!(
-                        &self.vis,
-                        type_alias_impl_trait,
-                        ty.span,
-                        "`impl Trait` in type aliases is unstable"
-                    );
+                    if self.in_associated_ty {
+                        gate_feature_post!(
+                            &self.vis,
+                            impl_trait_in_assoc_type,
+                            ty.span,
+                            "`impl Trait` in associated types is unstable"
+                        );
+                    } else {
+                        gate_feature_post!(
+                            &self.vis,
+                            type_alias_impl_trait,
+                            ty.span,
+                            "`impl Trait` in type aliases is unstable"
+                        );
+                    }
                 }
                 visit::walk_ty(self, ty);
             }
         }
-        ImplTraitVisitor { vis: self }.visit_ty(ty);
+        ImplTraitVisitor { vis: self, in_associated_ty }.visit_ty(ty);
     }
 
     fn check_late_bound_lifetime_defs(&self, params: &[ast::GenericParam]) {
@@ -294,7 +304,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             }
 
             ast::ItemKind::TyAlias(box ast::TyAlias { ty: Some(ty), .. }) => {
-                self.check_impl_trait(&ty)
+                self.check_impl_trait(&ty, false)
             }
 
             _ => {}
@@ -517,7 +527,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     );
                 }
                 if let Some(ty) = ty {
-                    self.check_impl_trait(ty);
+                    self.check_impl_trait(ty, true);
                 }
                 false
             }
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 426c6727adc..eea185c12dd 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -416,6 +416,8 @@ declare_features! (
     (active, half_open_range_patterns_in_slices, "1.66.0", Some(67264), None),
     /// Allows `if let` guard in match arms.
     (active, if_let_guard, "1.47.0", Some(51114), None),
+    /// Allows `impl Trait` to be used inside associated types (RFC 2515).
+    (active, impl_trait_in_assoc_type, "CURRENT_RUSTC_VERSION", Some(63063), None),
     /// Allows `impl Trait` as output type in `Fn` traits in return position of functions.
     (active, impl_trait_in_fn_trait_return, "1.64.0", Some(99697), None),
     /// Allows referencing `Self` and projections in impl-trait.
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 7affad9aa01..236f85a8e08 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -800,6 +800,7 @@ symbols! {
         ignore,
         impl_header_lifetime_elision,
         impl_lint_pass,
+        impl_trait_in_assoc_type,
         impl_trait_in_bindings,
         impl_trait_in_fn_trait_return,
         impl_trait_projections,