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Suppress duplicated errors for associated type bounds in object types

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This commit is contained in:
Michael Goulet
2023-02-14 20:07:33 +00:00
parent e7c490892f
commit deb135748d
6 changed files with 54 additions and 135 deletions
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75
compiler/rustc_ast_lowering/src/lib.rs
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@@ -1011,8 +1011,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
hir::TypeBindingKind::Equality { term }
}
AssocConstraintKind::Bound { bounds } => {
enum DesugarKind<'a> {
ImplTrait,
Error(&'a ImplTraitPosition),
Bound,
}
// Piggy-back on the `impl Trait` context to figure out the correct behavior.
let (desugar_to_impl_trait, itctx) = match itctx {
let desugar_kind = match itctx {
// We are in the return position:
//
// fn foo() -> impl Iterator<Item: Debug>
@@ -1021,7 +1027,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
//
// fn foo() -> impl Iterator<Item = impl Debug>
ImplTraitContext::ReturnPositionOpaqueTy { .. }
| ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
| ImplTraitContext::TypeAliasesOpaqueTy { .. } => DesugarKind::ImplTrait,
// We are in the argument position, but within a dyn type:
//
@@ -1030,7 +1036,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// so desugar to
//
// fn foo(x: dyn Iterator<Item = impl Debug>)
ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
ImplTraitContext::Universal if self.is_in_dyn_type => DesugarKind::ImplTrait,
// In `type Foo = dyn Iterator<Item: Debug>` we desugar to
// `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
@@ -1039,11 +1045,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
//
// FIXME: this is only needed until `impl Trait` is allowed in type aliases.
ImplTraitContext::Disallowed(position) if self.is_in_dyn_type => {
self.tcx.sess.emit_err(errors::MisplacedAssocTyBinding {
span: constraint.span,
position: DiagnosticArgFromDisplay(position),
});
(false, itctx)
DesugarKind::Error(position)
}
// We are in the parameter position, but not within a dyn type:
@@ -1053,35 +1055,46 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// so we leave it as is and this gets expanded in astconv to a bound like
// `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
// `impl Iterator`.
_ => (false, itctx),
_ => DesugarKind::Bound,
};
if desugar_to_impl_trait {
// Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
// constructing the HIR for `impl bounds...` and then lowering that.
match desugar_kind {
DesugarKind::ImplTrait => {
// Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
// constructing the HIR for `impl bounds...` and then lowering that.
let impl_trait_node_id = self.next_node_id();
let impl_trait_node_id = self.next_node_id();
self.with_dyn_type_scope(false, |this| {
let node_id = this.next_node_id();
let ty = this.lower_ty(
&Ty {
id: node_id,
kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
span: this.lower_span(constraint.span),
tokens: None,
},
itctx,
);
self.with_dyn_type_scope(false, |this| {
let node_id = this.next_node_id();
let ty = this.lower_ty(
&Ty {
id: node_id,
kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
span: this.lower_span(constraint.span),
tokens: None,
},
itctx,
);
hir::TypeBindingKind::Equality { term: ty.into() }
})
} else {
// Desugar `AssocTy: Bounds` into a type binding where the
// later desugars into a trait predicate.
let bounds = self.lower_param_bounds(bounds, itctx);
hir::TypeBindingKind::Equality { term: ty.into() }
})
}
DesugarKind::Bound => {
// Desugar `AssocTy: Bounds` into a type binding where the
// later desugars into a trait predicate.
let bounds = self.lower_param_bounds(bounds, itctx);
hir::TypeBindingKind::Constraint { bounds }
hir::TypeBindingKind::Constraint { bounds }
}
DesugarKind::Error(position) => {
self.tcx.sess.emit_err(errors::MisplacedAssocTyBinding {
span: constraint.span,
position: DiagnosticArgFromDisplay(position),
});
let err_ty = &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err));
hir::TypeBindingKind::Equality { term: err_ty.into() }
}
}
}
};