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Auto merge of #91403 - cjgillot:inherit-async, r=oli-obk

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Inherit lifetimes for async fn instead of duplicating them.

The current desugaring of `async fn foo<'a>(&usize) -> &u8` is equivalent to
```rust
fn foo<'a, '0>(&'0 usize) -> foo<'static, 'static>::Opaque<'a, '0, '_>;
type foo<'_a, '_0>::Opaque<'a, '0, '1> = impl Future<Output = &'1 u8>;
```
following the RPIT model.

Duplicating all the inherited lifetime parameters and setting the inherited version to `'static` makes lowering more complex and causes issues like #61949. This PR removes the duplication of inherited lifetimes to directly use
```rust
fn foo<'a, '0>(&'0 usize) -> foo<'a, '0>::Opaque<'_>;
type foo<'a, '0>::Opaque<'1> = impl Future<Output = &'1 u8>;
```
following the TAIT model.

Fixes https://github.com/rust-lang/rust/issues/61949
This commit is contained in:
bors 2022-02-12 21:42:10 +00:00
commit 3cfa4def7c
34 changed files with 227 additions and 281 deletions
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34
compiler/rustc_resolve/src/late/lifetimes.rs
View file

@ -729,9 +729,16 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
match item.kind {
hir::ItemKind::Fn(ref sig, ref generics, _) => {
self.missing_named_lifetime_spots.push(generics.into());
self.visit_early_late(None, item.hir_id(), &sig.decl, generics, |this| {
intravisit::walk_item(this, item);
});
self.visit_early_late(
None,
item.hir_id(),
&sig.decl,
generics,
sig.header.asyncness,
|this| {
intravisit::walk_item(this, item);
},
);
self.missing_named_lifetime_spots.pop();
}
@ -849,11 +856,16 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
match item.kind {
hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
self.visit_early_late(None, item.hir_id(), decl, generics, |this| {
hir::ForeignItemKind::Fn(ref decl, _, ref generics) => self.visit_early_late(
None,
item.hir_id(),
decl,
generics,
hir::IsAsync::NotAsync,
|this| {
intravisit::walk_foreign_item(this, item);
})
}
},
),
hir::ForeignItemKind::Static(..) => {
intravisit::walk_foreign_item(self, item);
}
@ -1130,6 +1142,7 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
trait_item.hir_id(),
&sig.decl,
&trait_item.generics,
sig.header.asyncness,
|this| intravisit::walk_trait_item(this, trait_item),
);
self.missing_named_lifetime_spots.pop();
@ -1199,6 +1212,7 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
impl_item.hir_id(),
&sig.decl,
&impl_item.generics,
sig.header.asyncness,
|this| intravisit::walk_impl_item(this, impl_item),
);
self.missing_named_lifetime_spots.pop();
@ -2159,11 +2173,15 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
hir_id: hir::HirId,
decl: &'tcx hir::FnDecl<'tcx>,
generics: &'tcx hir::Generics<'tcx>,
asyncness: hir::IsAsync,
walk: F,
) where
F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
{
insert_late_bound_lifetimes(self.map, decl, generics);
// Async fns need all their lifetime parameters to be early bound.
if asyncness != hir::IsAsync::Async {
insert_late_bound_lifetimes(self.map, decl, generics);
}
// Find the start of nested early scopes, e.g., in methods.
let mut next_early_index = 0;