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Fixed up some comments.

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This commit is contained in:
Alexander Regueiro 2019-05-10 03:46:39 +01:00
parent 538ebd197c
commit 5bf5994d92
1 changed files with 14 additions and 19 deletions
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33
src/librustc/hir/lowering.rs
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@ -1381,33 +1381,30 @@ impl<'a> LoweringContext<'a> {
let ty = match c.kind {
AssocTyConstraintKind::Equality { ref ty } => self.lower_ty(ty, itctx),
AssocTyConstraintKind::Bound { ref bounds } => {
// Piggy-back on the impl trait context to figure out
// the correct behavior.
// Piggy-back on the `impl Trait` context to figure out the correct behavior.
let (desugar_to_impl_trait, itctx) = match itctx {
// We are in the return position:
//
// fn foo() -> impl Iterator<Item: Debug>
// fn foo() -> impl Iterator<Item: Debug>
//
// so desugar to
//
// fn foo() -> impl Iterator<Item = impl Debug>
// fn foo() -> impl Iterator<Item = impl Debug>
ImplTraitContext::Existential(_) => (true, itctx),
// We are in the argument position, but within a dyn type:
//
// fn foo(x: dyn Iterator<Item: Debug>)
// fn foo(x: dyn Iterator<Item: Debug>)
//
// so desugar to
//
// fn foo(x: dyn Iterator<Item = impl Debug>)
// fn foo(x: dyn Iterator<Item = impl Debug>)
ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
// In `type Foo = dyn Iterator<Item: Debug>` we
// desugar to `type Foo = dyn Iterator<Item = impl
// Debug>` but we have to override the "impl trait
// context" to permit `impl Debug` in this
// position (it desugars then to an existential
// type).
// In `type Foo = dyn Iterator<Item: Debug>` we desugar to
// `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
// "impl trait context" to permit `impl Debug` in this position (it desugars
// then to an existential type).
//
// FIXME: this is only needed until `impl Trait` is allowed in type aliases.
ImplTraitContext::Disallowed(_) if self.is_in_dyn_type =>
@ -1415,19 +1412,17 @@ impl<'a> LoweringContext<'a> {
// We are in the argument position, but not within a dyn type:
//
// fn foo(x: impl Iterator<Item: Debug>)
// 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
// 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),
};
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.
// 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.sess.next_node_id();
let parent_def_index = self.current_hir_id_owner.last().unwrap().0;