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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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69
compiler/rustc_ast_lowering/src/lib.rs
View file

@ -1659,11 +1659,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// When we create the opaque type for this async fn, it is going to have
// to capture all the lifetimes involved in the signature (including in the
// return type). This is done by introducing lifetime parameters for:
// return type). This is done by:
//
// - all the explicitly declared lifetimes from the impl and function itself;
// - all the elided lifetimes in the fn arguments;
// - all the elided lifetimes in the return type.
// - making the opaque type inherit all lifetime parameters from its parent;
// - make all the elided lifetimes in the fn arguments into parameters;
// - manually introducing parameters on the opaque type for elided
// lifetimes in the return type.
//
// So for example in this snippet:
//
@ -1679,14 +1680,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// we would create an opaque type like:
//
// ```
// type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
// type Foo<'a>::bar<'b, '0, '1>::Bar<'2> = impl Future<Output = &'2 u32>;
// ```
//
// and we would then desugar `bar` to the equivalent of:
//
// ```rust
// impl<'a> Foo<'a> {
// fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
// fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'_>
// }
// ```
//
@ -1694,29 +1695,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// this is because the elided lifetimes from the return type
// should be figured out using the ordinary elision rules, and
// this desugaring achieves that.
debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", self.in_scope_lifetimes);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", self.lifetimes_to_define);
// Calculate all the lifetimes that should be captured
// by the opaque type. This should include all in-scope
// lifetime parameters, including those defined in-band.
//
// `lifetime_params` is a vector of tuple (span, parameter name, lifetime name).
// Input lifetime like `'a` or `'1`:
let mut lifetime_params: Vec<_> = self
.in_scope_lifetimes
.iter()
.cloned()
.map(|name| (name.ident().span, name, hir::LifetimeName::Param(name)))
.chain(
self.lifetimes_to_define
.iter()
.map(|&(span, name)| (span, name, hir::LifetimeName::Param(name))),
)
.collect();
let mut lifetime_params = Vec::new();
self.with_hir_id_owner(opaque_ty_node_id, |this| {
// We have to be careful to get elision right here. The
// idea is that we create a lifetime parameter for each
@ -1735,16 +1714,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", lifetimes_to_define);
lifetime_params.extend(
// Output lifetime like `'_`:
lifetimes_to_define
.into_iter()
.map(|(span, name)| (span, name, hir::LifetimeName::Implicit(false))),
);
// Output lifetime like `'_`:
lifetime_params = lifetimes_to_define;
debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
let generic_params =
this.arena.alloc_from_iter(lifetime_params.iter().map(|&(span, hir_name, _)| {
this.arena.alloc_from_iter(lifetime_params.iter().map(|&(span, hir_name)| {
this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_id)
}));
@ -1762,28 +1737,22 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
});
// As documented above on the variable
// `input_lifetimes_count`, we need to create the lifetime
// arguments to our opaque type. Continuing with our example,
// we're creating the type arguments for the return type:
// We need to create the lifetime arguments to our opaque type.
// Continuing with our example, we're creating the type arguments
// for the return type:
//
// ```
// Bar<'a, 'b, '0, '1, '_>
// For<'a>::bar<'b, '0, '1>::Bar<'_>
// ```
//
// For the "input" lifetime parameters, we wish to create
// references to the parameters themselves, including the
// "implicit" ones created from parameter types (`'a`, `'b`,
// '`0`, `'1`).
//
// For the "output" lifetime parameters, we just want to
// generate `'_`.
// For the "input" lifetime parameters are inherited automatically.
// For the "output" lifetime parameters, we just want to generate `'_`.
let generic_args =
self.arena.alloc_from_iter(lifetime_params.into_iter().map(|(span, _, name)| {
self.arena.alloc_from_iter(lifetime_params.into_iter().map(|(span, _)| {
GenericArg::Lifetime(hir::Lifetime {
hir_id: self.next_id(),
span: self.lower_span(span),
name,
name: hir::LifetimeName::Implicit(false),
})
}));

18
compiler/rustc_borrowck/src/region_infer/mod.rs
View file

@ -2156,6 +2156,24 @@ impl<'tcx> RegionInferenceContext<'tcx> {
}
}
// When in async fn, prefer errors that come from inside the closure.
if !categorized_path[i].from_closure {
let span = categorized_path.iter().find_map(|p| {
if p.from_closure
&& p.category == categorized_path[i].category
&& categorized_path[i].cause.span.contains(p.cause.span)
{
Some(p.cause.span)
} else {
None
}
});
if let Some(span) = span {
categorized_path[i].cause.span = span;
}
}
return categorized_path[i].clone();
}

6
compiler/rustc_error_codes/src/error_codes/E0760.md
View file

@ -1,4 +1,4 @@
`async fn`/`impl trait` return type cannot contain a projection
`impl trait` return type cannot contain a projection
or `Self` that references lifetimes from a parent scope.
Erroneous code example:
@ -7,7 +7,7 @@ Erroneous code example:
struct S<'a>(&'a i32);
impl<'a> S<'a> {
async fn new(i: &'a i32) -> Self {
fn new(i: &'a i32) -> impl Into<Self> {
S(&22)
}
}
@ -19,7 +19,7 @@ To fix this error we need to spell out `Self` to `S<'a>`:
struct S<'a>(&'a i32);
impl<'a> S<'a> {
async fn new(i: &'a i32) -> S<'a> {
fn new(i: &'a i32) -> impl Into<S<'a>> {
S(&22)
}
}

4
compiler/rustc_infer/src/infer/opaque_types.rs
View file

@ -276,7 +276,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
debug!(?concrete_ty);
let first_own_region = match opaque_defn.origin {
hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) => {
hir::OpaqueTyOrigin::FnReturn(..) => {
// We lower
//
// fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
@ -291,7 +291,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
}
// These opaque type inherit all lifetime parameters from their
// parent, so we have to check them all.
hir::OpaqueTyOrigin::TyAlias => 0,
hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::TyAlias => 0,
};
// For a case like `impl Foo<'a, 'b>`, we would generate a constraint

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;

15
compiler/rustc_typeck/src/astconv/mod.rs
View file

@ -2408,16 +2408,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
let def_id = item_id.def_id.to_def_id();
match opaque_ty.kind {
hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => self
.impl_trait_ty_to_ty(
def_id,
lifetimes,
matches!(
origin,
hir::OpaqueTyOrigin::FnReturn(..)
| hir::OpaqueTyOrigin::AsyncFn(..)
),
),
hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
let replace_parent_lifetimes =
matches!(origin, hir::OpaqueTyOrigin::FnReturn(..));
self.impl_trait_ty_to_ty(def_id, lifetimes, replace_parent_lifetimes)
}
ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
}
}

15
compiler/rustc_typeck/src/check/check.rs
View file

@ -535,10 +535,8 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
}
}
if let ItemKind::OpaqueTy(hir::OpaqueTy {
origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
..
}) = item.kind
if let ItemKind::OpaqueTy(hir::OpaqueTy { origin: hir::OpaqueTyOrigin::FnReturn(..), .. }) =
item.kind
{
let mut visitor = ProhibitOpaqueVisitor {
opaque_identity_ty: tcx.mk_opaque(
@ -560,20 +558,13 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
if let Some(ty) = prohibit_opaque.break_value() {
visitor.visit_item(&item);
let is_async = match item.kind {
ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
matches!(origin, hir::OpaqueTyOrigin::AsyncFn(..))
}
_ => unreachable!(),
};
let mut err = struct_span_err!(
tcx.sess,
span,
E0760,
"`{}` return type cannot contain a projection or `Self` that references lifetimes from \
"`impl Trait` return type cannot contain a projection or `Self` that references lifetimes from \
a parent scope",
if is_async { "async fn" } else { "impl Trait" },
);
for (span, name) in visitor.selftys {

5
compiler/rustc_typeck/src/collect.rs
View file

@ -2162,8 +2162,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
generics
}
ItemKind::OpaqueTy(OpaqueTy {
origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
..
origin: hir::OpaqueTyOrigin::FnReturn(..), ..
}) => {
// return-position impl trait
//
@ -2183,7 +2182,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
}
ItemKind::OpaqueTy(OpaqueTy {
ref generics,
origin: hir::OpaqueTyOrigin::TyAlias,
origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::TyAlias,
..
}) => {
// type-alias impl trait