No more associated type bounds in dyn trait

Author: compiler-errors

compiler/rustc_ast_lowering/messages.ftl

@@ -8,6 +8,9 @@ ast_lowering_arbitrary_expression_in_pattern =
 
 ast_lowering_argument = argument
 
+ast_lowering_assoc_ty_binding_in_dyn =
+    associated type bounds are not allowed in `dyn` types
+
 ast_lowering_assoc_ty_parentheses =
     parenthesized generic arguments cannot be used in associated type constraints
 
@@ -100,9 +103,6 @@ ast_lowering_match_arm_with_no_body =
     `match` arm with no body
     .suggestion = add a body after the pattern
 
-ast_lowering_misplaced_assoc_ty_binding =
-    associated type bounds are only allowed in where clauses and function signatures, not in {$position}
-
 ast_lowering_misplaced_double_dot =
     `..` patterns are not allowed here
     .note = only allowed in tuple, tuple struct, and slice patterns

compiler/rustc_ast_lowering/src/errors.rs

@@ -98,11 +98,10 @@ pub struct MisplacedImplTrait<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_lowering_misplaced_assoc_ty_binding)]
-pub struct MisplacedAssocTyBinding<'a> {
+#[diag(ast_lowering_assoc_ty_binding_in_dyn)]
+pub struct MisplacedAssocTyBinding {
     #[primary_span]
     pub span: Span,
-    pub position: DiagnosticArgFromDisplay<'a>,
 }
 
 #[derive(Diagnostic, Clone, Copy)]

compiler/rustc_ast_lowering/src/lib.rs

@@ -1079,14 +1079,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 hir::TypeBindingKind::Equality { term }
             }
             AssocConstraintKind::Bound { bounds } => {
-                enum DesugarKind<'a> {
+                enum DesugarKind {
                     ImplTrait,
-                    Error(&'a ImplTraitPosition),
+                    Error,
                     Bound,
                 }
 
                 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
                 let desugar_kind = match itctx {
+                    _ if self.is_in_dyn_type => DesugarKind::Error,
+
                     // We are in the return position:
                     //
                     //     fn foo() -> impl Iterator<Item: Debug>
@@ -1097,19 +1099,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     ImplTraitContext::ReturnPositionOpaqueTy { .. }
                     | ImplTraitContext::TypeAliasesOpaqueTy { .. } => DesugarKind::ImplTrait,
 
-                    // We are in the argument position, but within a dyn type:
-                    //
-                    //     fn foo(x: dyn Iterator<Item: Debug>)
-                    //
-                    // so desugar to
-                    //
-                    //     fn foo(x: dyn Iterator<Item = impl Debug>)
-                    ImplTraitContext::Universal if self.is_in_dyn_type => DesugarKind::ImplTrait,
-
-                    ImplTraitContext::Disallowed(position) if self.is_in_dyn_type => {
-                        DesugarKind::Error(position)
-                    }
-
                     // We are in the parameter position, but not within a dyn type:
                     //
                     //     fn foo(x: impl Iterator<Item: Debug>)
@@ -1154,11 +1143,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                         hir::TypeBindingKind::Constraint { bounds }
                     }
-                    DesugarKind::Error(position) => {
-                        let guar = self.dcx().emit_err(errors::MisplacedAssocTyBinding {
-                            span: constraint.span,
-                            position: DiagnosticArgFromDisplay(position),
-                        });
+                    DesugarKind::Error => {
+                        let guar = self
+                            .dcx()
+                            .emit_err(errors::MisplacedAssocTyBinding { span: constraint.span });
                         let err_ty =
                             &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
                         hir::TypeBindingKind::Equality { term: err_ty.into() }

tests/ui/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.rs

@@ -28,9 +28,9 @@ impl Bar for AssocNoCopy {
 
 impl Thing for AssocNoCopy {
     type Out = Box<dyn Bar<Assoc: Copy>>;
+    //~^ ERROR associated type bounds are not allowed in `dyn` types
 
     fn func() -> Self::Out {
-        //~^ ERROR the trait bound `String: Copy` is not satisfied
         Box::new(AssocNoCopy)
     }
 }

tests/ui/associated-type-bounds/assoc-type-eq-with-dyn-atb-fail.stderr

@@ -1,9 +1,8 @@
-error[E0277]: the trait bound `String: Copy` is not satisfied
-  --> $DIR/assoc-type-eq-with-dyn-atb-fail.rs:32:18
+error: associated type bounds are not allowed in `dyn` types
+  --> $DIR/assoc-type-eq-with-dyn-atb-fail.rs:30:28
    |
-LL |     fn func() -> Self::Out {
-   |                  ^^^^^^^^^ the trait `Copy` is not implemented for `String`
+LL |     type Out = Box<dyn Bar<Assoc: Copy>>;
+   |                            ^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0277`.

tests/ui/associated-type-bounds/bad-universal-in-dyn-in-where-clause.rs

@@ -7,7 +7,7 @@ trait B {
 fn f()
 where
     dyn for<'j> B<AssocType: 'j>:,
-    //~^ ERROR associated type bounds are only allowed in where clauses and function signatures
+    //~^ ERROR associated type bounds are not allowed in `dyn` types
 {
 }
 

tests/ui/associated-type-bounds/bad-universal-in-dyn-in-where-clause.stderr

@@ -1,4 +1,4 @@
-error: associated type bounds are only allowed in where clauses and function signatures, not in bounds
+error: associated type bounds are not allowed in `dyn` types
   --> $DIR/bad-universal-in-dyn-in-where-clause.rs:9:19
    |
 LL |     dyn for<'j> B<AssocType: 'j>:,

tests/ui/associated-type-bounds/bad-universal-in-impl-sig.rs

@@ -8,6 +8,6 @@ trait Trait2 {}
 
 // It's not possible to insert a universal `impl Trait` here!
 impl dyn Trait<Item: Trait2> {}
-//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
+//~^ ERROR associated type bounds are not allowed in `dyn` types
 
 fn main() {}

tests/ui/associated-type-bounds/bad-universal-in-impl-sig.stderr

@@ -1,4 +1,4 @@
-error: associated type bounds are only allowed in where clauses and function signatures, not in impl headers
+error: associated type bounds are not allowed in `dyn` types
   --> $DIR/bad-universal-in-impl-sig.rs:10:16
    |
 LL | impl dyn Trait<Item: Trait2> {}

tests/ui/associated-type-bounds/duplicate.rs

@@ -264,11 +264,4 @@ trait TRA3 {
     //~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
 }
 
-type TADyn1 = dyn Iterator<Item: Copy, Item: Send>;
-//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
-type TADyn2 = Box<dyn Iterator<Item: Copy, Item: Copy>>;
-//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
-type TADyn3 = dyn Iterator<Item: 'static, Item: 'static>;
-//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
-
 fn main() {}