From 62f89e05918227276ea182e5617020a82234b52b Mon Sep 17 00:00:00 2001 From: David Wood Date: Sun, 21 Jul 2019 14:37:13 +0100 Subject: [PATCH] typeck: Prohibit RPIT types that inherit lifetimes This commit prohibits return position `impl Trait` types that "inherit lifetimes" from the parent scope. The intent is to forbid cases that are challenging until they can be addressed properly. --- src/librustc_typeck/check/mod.rs | 81 +++++++++++++++++++ .../issue-61949-self-return-type.rs | 28 +++++++ .../issue-61949-self-return-type.stderr | 8 ++ .../ui/impl-trait/bound-normalization-fail.rs | 4 +- .../bound-normalization-fail.stderr | 14 +++- 5 files changed, 130 insertions(+), 5 deletions(-) create mode 100644 src/test/ui/async-await/issue-61949-self-return-type.rs create mode 100644 src/test/ui/async-await/issue-61949-self-return-type.stderr diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs index 77d45cfa63c10..0b019a5de2594 100644 --- a/src/librustc_typeck/check/mod.rs +++ b/src/librustc_typeck/check/mod.rs @@ -1315,7 +1315,88 @@ fn check_union(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) { check_packed(tcx, span, def_id); } +/// Checks that an opaque type does not contain cycles and does not use `Self` or `T::Foo` +/// projections that would result in "inheriting lifetimes". fn check_opaque<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, substs: SubstsRef<'tcx>, span: Span) { + check_opaque_for_inheriting_lifetimes(tcx, def_id, span); + check_opaque_for_cycles(tcx, def_id, substs, span); +} + +/// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result +/// in "inheriting lifetimes". +fn check_opaque_for_inheriting_lifetimes( + tcx: TyCtxt<'tcx>, + def_id: DefId, + span: Span, +) { + let item = tcx.hir().expect_item( + tcx.hir().as_local_hir_id(def_id).expect("existential type is not local")); + debug!("check_opaque_for_inheriting_lifetimes: def_id={:?} span={:?} item={:?}", + def_id, span, item); + + #[derive(Debug)] + struct ProhibitOpaqueVisitor<'tcx> { + opaque_identity_ty: Ty<'tcx>, + generics: &'tcx ty::Generics, + }; + + impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueVisitor<'tcx> { + fn visit_ty(&mut self, t: Ty<'tcx>) -> bool { + debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t); + if t == self.opaque_identity_ty { false } else { t.super_visit_with(self) } + } + + fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { + debug!("check_opaque_for_inheriting_lifetimes: (visit_region) r={:?}", r); + if let RegionKind::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = r { + return *index < self.generics.parent_count as u32; + } + + r.super_visit_with(self) + } + } + + let prohibit_opaque = match item.node { + ItemKind::Existential(hir::ExistTy { origin: hir::ExistTyOrigin::AsyncFn, .. }) | + ItemKind::Existential(hir::ExistTy { origin: hir::ExistTyOrigin::ReturnImplTrait, .. }) => { + let mut visitor = ProhibitOpaqueVisitor { + opaque_identity_ty: tcx.mk_opaque( + def_id, InternalSubsts::identity_for_item(tcx, def_id)), + generics: tcx.generics_of(def_id), + }; + debug!("check_opaque_for_inheriting_lifetimes: visitor={:?}", visitor); + + tcx.predicates_of(def_id).predicates.iter().any( + |(predicate, _)| predicate.visit_with(&mut visitor)) + }, + _ => false, + }; + + debug!("check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}", prohibit_opaque); + if prohibit_opaque { + let is_async = match item.node { + ItemKind::Existential(hir::ExistTy { origin, .. }) => match origin { + hir::ExistTyOrigin::AsyncFn => true, + _ => false, + }, + _ => unreachable!(), + }; + + tcx.sess.span_err(span, &format!( + "`{}` return type cannot contain a projection or `Self` that references lifetimes from \ + a parent scope", + if is_async { "async fn" } else { "impl Trait" }, + )); + } +} + +/// Checks that an opaque type does not contain cycles. +fn check_opaque_for_cycles<'tcx>( + tcx: TyCtxt<'tcx>, + def_id: DefId, + substs: SubstsRef<'tcx>, + span: Span, +) { if let Err(partially_expanded_type) = tcx.try_expand_impl_trait_type(def_id, substs) { let mut err = struct_span_err!( tcx.sess, span, E0720, diff --git a/src/test/ui/async-await/issue-61949-self-return-type.rs b/src/test/ui/async-await/issue-61949-self-return-type.rs new file mode 100644 index 0000000000000..c5a66d5d4a312 --- /dev/null +++ b/src/test/ui/async-await/issue-61949-self-return-type.rs @@ -0,0 +1,28 @@ +// ignore-tidy-linelength +// edition:2018 +#![feature(async_await)] + +// This test checks that `Self` is prohibited as a return type. See #61949 for context. + +pub struct Foo<'a> { + pub bar: &'a i32, +} + +impl<'a> Foo<'a> { + pub async fn new(_bar: &'a i32) -> Self { + //~^ ERROR `async fn` return type cannot contain a projection or `Self` that references lifetimes from a parent scope + Foo { + bar: &22 + } + } +} + +async fn foo() { + let x = { + let bar = 22; + Foo::new(&bar).await + }; + drop(x); +} + +fn main() { } diff --git a/src/test/ui/async-await/issue-61949-self-return-type.stderr b/src/test/ui/async-await/issue-61949-self-return-type.stderr new file mode 100644 index 0000000000000..a9ae544502d08 --- /dev/null +++ b/src/test/ui/async-await/issue-61949-self-return-type.stderr @@ -0,0 +1,8 @@ +error: `async fn` return type cannot contain a projection or `Self` that references lifetimes from a parent scope + --> $DIR/issue-61949-self-return-type.rs:12:40 + | +LL | pub async fn new(_bar: &'a i32) -> Self { + | ^^^^ + +error: aborting due to previous error + diff --git a/src/test/ui/impl-trait/bound-normalization-fail.rs b/src/test/ui/impl-trait/bound-normalization-fail.rs index 476ae62fa0fa4..98c3242fba886 100644 --- a/src/test/ui/impl-trait/bound-normalization-fail.rs +++ b/src/test/ui/impl-trait/bound-normalization-fail.rs @@ -1,4 +1,5 @@ // compile-fail +// ignore-tidy-linelength // edition:2018 #![feature(async_await)] @@ -45,7 +46,8 @@ mod lifetimes { /// Missing bound constraining `Assoc`, `T::Assoc` can't be normalized further. fn foo2_fail<'a, T: Trait<'a>>() -> impl FooLike { - //~^ ERROR: type mismatch + //~^ ERROR: type mismatch + //~^^ ERROR `impl Trait` return type cannot contain a projection or `Self` that references lifetimes from a parent scope Foo(()) } } diff --git a/src/test/ui/impl-trait/bound-normalization-fail.stderr b/src/test/ui/impl-trait/bound-normalization-fail.stderr index fa2dd20a6eed7..22ea8116fe656 100644 --- a/src/test/ui/impl-trait/bound-normalization-fail.stderr +++ b/src/test/ui/impl-trait/bound-normalization-fail.stderr @@ -1,11 +1,11 @@ warning: the feature `impl_trait_in_bindings` is incomplete and may cause the compiler to crash - --> $DIR/bound-normalization-fail.rs:6:12 + --> $DIR/bound-normalization-fail.rs:7:12 | LL | #![feature(impl_trait_in_bindings)] | ^^^^^^^^^^^^^^^^^^^^^^ error[E0271]: type mismatch resolving ` as FooLike>::Output == ::Assoc` - --> $DIR/bound-normalization-fail.rs:30:32 + --> $DIR/bound-normalization-fail.rs:31:32 | LL | fn foo_fail() -> impl FooLike { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected (), found associated type @@ -14,8 +14,14 @@ LL | fn foo_fail() -> impl FooLike { found type `::Assoc` = note: the return type of a function must have a statically known size +error: `impl Trait` return type cannot contain a projection or `Self` that references lifetimes from a parent scope + --> $DIR/bound-normalization-fail.rs:48:41 + | +LL | fn foo2_fail<'a, T: Trait<'a>>() -> impl FooLike { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + error[E0271]: type mismatch resolving ` as FooLike>::Output == >::Assoc` - --> $DIR/bound-normalization-fail.rs:47:41 + --> $DIR/bound-normalization-fail.rs:48:41 | LL | fn foo2_fail<'a, T: Trait<'a>>() -> impl FooLike { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected (), found associated type @@ -24,6 +30,6 @@ LL | fn foo2_fail<'a, T: Trait<'a>>() -> impl FooLike { found type `>::Assoc` = note: the return type of a function must have a statically known size -error: aborting due to 2 previous errors +error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0271`.