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This commit is contained in:
Michael Goulet
2024-02-06 19:48:16 +00:00
parent 973bbfbd23
commit fde695a2d1
7 changed files with 43 additions and 57 deletions
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63
compiler/rustc_ast_lowering/src/lib.rs
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@@ -1084,41 +1084,38 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
hir::TypeBindingKind::Equality { term }
}
AssocConstraintKind::Bound { bounds } => {
enum DesugarKind {
Error,
Bound,
}
// Disallow ATB in dyn types
if self.is_in_dyn_type {
let suggestion = match itctx {
ImplTraitContext::ReturnPositionOpaqueTy { .. }
| ImplTraitContext::TypeAliasesOpaqueTy { .. }
| ImplTraitContext::Universal => {
let bound_end_span = constraint
.gen_args
.as_ref()
.map_or(constraint.ident.span, |args| args.span());
if bound_end_span.eq_ctxt(constraint.span) {
Some(self.tcx.sess.source_map().next_point(bound_end_span))
} else {
None
}
}
_ => None,
};
// 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,
let guar = self.dcx().emit_err(errors::MisplacedAssocTyBinding {
span: constraint.span,
suggestion,
});
let err_ty =
&*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
hir::TypeBindingKind::Equality { term: err_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);
// We are in the parameter position, but not within a dyn type:
//
// fn foo(x: impl Iterator<Item: Debug>)
//
// 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`.
_ => DesugarKind::Bound,
};
match desugar_kind {
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 }
}
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() }
}
hir::TypeBindingKind::Constraint { bounds }
}
}
};