From cf031a3355f677ed1a44e31cbc2b2d84f3cb13b6 Mon Sep 17 00:00:00 2001 From: Arpad Borsos Date: Sun, 4 Dec 2022 12:32:15 +0100 Subject: [PATCH] Replace usage of `ResumeTy` in async lowering with `Context` Replaces using `ResumeTy` / `get_context` in favor of using `&'static mut Context<'_>`. Usage of the `'static` lifetime here is technically "cheating", and replaces the raw pointer in `ResumeTy` and the `get_context` fn that pulls the correct lifetimes out of thin air. --- compiler/rustc_ast_lowering/src/expr.rs | 57 ++++++++++++------- compiler/rustc_hir/src/lang_items.rs | 3 +- compiler/rustc_span/src/symbol.rs | 3 +- library/core/src/future/mod.rs | 10 +++- library/core/src/task/wake.rs | 1 + .../async-await-let-else.drop-tracking.stderr | 2 +- .../issue-68112.drop_tracking.stderr | 2 +- .../issue-68112.no_drop_tracking.stderr | 2 +- .../issue-69446-fnmut-capture.stderr | 3 + ...e-70935-complex-spans.drop_tracking.stderr | 2 +- ...l-drop-partial-reinit.drop_tracking.stderr | 2 +- ...rop-partial-reinit.no_drop_tracking.stderr | 2 +- .../closure-in-projection-issue-97405.rs | 4 +- .../closure-in-projection-issue-97405.stderr | 20 ++++--- 14 files changed, 70 insertions(+), 43 deletions(-) diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs index 695ccec0b1cb1..9974ebff311fb 100644 --- a/compiler/rustc_ast_lowering/src/expr.rs +++ b/compiler/rustc_ast_lowering/src/expr.rs @@ -16,7 +16,7 @@ use rustc_hir::def::Res; use rustc_hir::definitions::DefPathData; use rustc_session::errors::report_lit_error; use rustc_span::source_map::{respan, DesugaringKind, Span, Spanned}; -use rustc_span::symbol::{sym, Ident}; +use rustc_span::symbol::{kw, sym, Ident}; use rustc_span::DUMMY_SP; use thin_vec::thin_vec; @@ -594,14 +594,38 @@ impl<'hir> LoweringContext<'_, 'hir> { ) -> hir::ExprKind<'hir> { let output = ret_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span))); - // Resume argument type: `ResumeTy` - let unstable_span = - self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone()); - let resume_ty = hir::QPath::LangItem(hir::LangItem::ResumeTy, unstable_span, None); + // Resume argument type, which should be `&mut Context<'_>`. + // NOTE: Using the `'static` lifetime here is technically cheating. + // The `Future::poll` argument really is `&'a mut Context<'b>`, but we cannot + // express the fact that we are not storing it across yield-points yet, + // and we would thus run into lifetime errors. + // See . + // Our lowering makes sure we are not mis-using the `_task_context` input type + // in the sense that we are indeed not using it across yield points. We + // get a fresh `&mut Context` for each resume / call of `Future::poll`. + // This "cheating" was previously done with a `ResumeTy` that contained a raw + // pointer, and a `get_context` accessor that pulled the `Context` lifetimes + // out of thin air. + let context_lifetime_ident = Ident::with_dummy_span(kw::StaticLifetime); + let context_lifetime = self.arena.alloc(hir::Lifetime { + hir_id: self.next_id(), + ident: context_lifetime_ident, + res: hir::LifetimeName::Static, + }); + let context_path = + hir::QPath::LangItem(hir::LangItem::Context, self.lower_span(span), None); + let context_ty = hir::MutTy { + ty: self.arena.alloc(hir::Ty { + hir_id: self.next_id(), + kind: hir::TyKind::Path(context_path), + span: self.lower_span(span), + }), + mutbl: hir::Mutability::Mut, + }; let input_ty = hir::Ty { hir_id: self.next_id(), - kind: hir::TyKind::Path(resume_ty), - span: unstable_span, + kind: hir::TyKind::Rptr(context_lifetime, context_ty), + span: self.lower_span(span), }; // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`. @@ -659,12 +683,9 @@ impl<'hir> LoweringContext<'_, 'hir> { .map_or(false, |attrs| attrs.into_iter().any(|attr| attr.has_name(sym::track_caller))); let hir_id = self.lower_node_id(closure_node_id); + let unstable_span = + self.mark_span_with_reason(DesugaringKind::Async, span, self.allow_gen_future.clone()); if track_caller { - let unstable_span = self.mark_span_with_reason( - DesugaringKind::Async, - span, - self.allow_gen_future.clone(), - ); self.lower_attrs( hir_id, &[Attribute { @@ -711,7 +732,7 @@ impl<'hir> LoweringContext<'_, 'hir> { /// mut __awaitee => loop { /// match unsafe { ::std::future::Future::poll( /// <::std::pin::Pin>::new_unchecked(&mut __awaitee), - /// ::std::future::get_context(task_context), + /// task_context, /// ) } { /// ::std::task::Poll::Ready(result) => break result, /// ::std::task::Poll::Pending => {} @@ -752,7 +773,7 @@ impl<'hir> LoweringContext<'_, 'hir> { // unsafe { // ::std::future::Future::poll( // ::std::pin::Pin::new_unchecked(&mut __awaitee), - // ::std::future::get_context(task_context), + // task_context, // ) // } let poll_expr = { @@ -770,16 +791,10 @@ impl<'hir> LoweringContext<'_, 'hir> { arena_vec![self; ref_mut_awaitee], Some(expr_hir_id), ); - let get_context = self.expr_call_lang_item_fn_mut( - gen_future_span, - hir::LangItem::GetContext, - arena_vec![self; task_context], - Some(expr_hir_id), - ); let call = self.expr_call_lang_item_fn( span, hir::LangItem::FuturePoll, - arena_vec![self; new_unchecked, get_context], + arena_vec![self; new_unchecked, task_context], Some(expr_hir_id), ); self.arena.alloc(self.expr_unsafe(call)) diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs index 038509031b180..b51257df713ea 100644 --- a/compiler/rustc_hir/src/lang_items.rs +++ b/compiler/rustc_hir/src/lang_items.rs @@ -286,10 +286,9 @@ language_item_table! { // FIXME(swatinem): the following lang items are used for async lowering and // should become obsolete eventually. - ResumeTy, sym::ResumeTy, resume_ty, Target::Struct, GenericRequirement::None; IdentityFuture, sym::identity_future, identity_future_fn, Target::Fn, GenericRequirement::None; - GetContext, sym::get_context, get_context_fn, Target::Fn, GenericRequirement::None; + Context, sym::Context, context, Target::Struct, GenericRequirement::None; FuturePoll, sym::poll, future_poll_fn, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None; FromFrom, sym::from, from_fn, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None; diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs index 9e446c96db319..6125384549723 100644 --- a/compiler/rustc_span/src/symbol.rs +++ b/compiler/rustc_span/src/symbol.rs @@ -165,6 +165,7 @@ symbols! { Capture, Center, Clone, + Context, Continue, Copy, Count, @@ -264,7 +265,6 @@ symbols! { Relaxed, Release, Result, - ResumeTy, Return, Right, Rust, @@ -754,7 +754,6 @@ symbols! { generic_associated_types_extended, generic_const_exprs, generic_param_attrs, - get_context, global_allocator, global_asm, globs, diff --git a/library/core/src/future/mod.rs b/library/core/src/future/mod.rs index f2b961d62e00c..2a8e12fd4cf60 100644 --- a/library/core/src/future/mod.rs +++ b/library/core/src/future/mod.rs @@ -44,7 +44,7 @@ pub use poll_fn::{poll_fn, PollFn}; /// non-Send/Sync as well, and we don't want that. /// /// It also simplifies the HIR lowering of `.await`. -#[cfg_attr(not(bootstrap), lang = "ResumeTy")] +// FIXME(swatinem): This type can be removed when bumping the bootstrap compiler #[doc(hidden)] #[unstable(feature = "gen_future", issue = "50547")] #[derive(Debug, Copy, Clone)] @@ -61,6 +61,7 @@ unsafe impl Sync for ResumeTy {} /// This function returns a `GenFuture` underneath, but hides it in `impl Trait` to give /// better error messages (`impl Future` rather than `GenFuture<[closure.....]>`). // This is `const` to avoid extra errors after we recover from `const async fn` +// FIXME(swatinem): This fn can be removed when bumping the bootstrap compiler #[cfg_attr(bootstrap, lang = "from_generator")] #[doc(hidden)] #[unstable(feature = "gen_future", issue = "50547")] @@ -102,7 +103,8 @@ where GenFuture(gen) } -#[lang = "get_context"] +// FIXME(swatinem): This fn can be removed when bumping the bootstrap compiler +#[cfg_attr(bootstrap, lang = "get_context")] #[doc(hidden)] #[unstable(feature = "gen_future", issue = "50547")] #[must_use] @@ -113,6 +115,10 @@ pub unsafe fn get_context<'a, 'b>(cx: ResumeTy) -> &'a mut Context<'b> { unsafe { &mut *cx.0.as_ptr().cast() } } +// FIXME(swatinem): This fn is currently needed to work around shortcomings +// in type and lifetime inference. +// See the comment at the bottom of `LoweringContext::make_async_expr` and +// . #[cfg_attr(not(bootstrap), lang = "identity_future")] #[doc(hidden)] #[unstable(feature = "gen_future", issue = "50547")] diff --git a/library/core/src/task/wake.rs b/library/core/src/task/wake.rs index 0cff972df3a5a..9ab9b0ba1c797 100644 --- a/library/core/src/task/wake.rs +++ b/library/core/src/task/wake.rs @@ -174,6 +174,7 @@ impl RawWakerVTable { /// Currently, `Context` only serves to provide access to a [`&Waker`](Waker) /// which can be used to wake the current task. #[stable(feature = "futures_api", since = "1.36.0")] +#[cfg_attr(not(bootstrap), lang = "Context")] pub struct Context<'a> { waker: &'a Waker, // Ensure we future-proof against variance changes by forcing diff --git a/src/test/ui/async-await/async-await-let-else.drop-tracking.stderr b/src/test/ui/async-await/async-await-let-else.drop-tracking.stderr index 3be7f370da3f5..616623ee07759 100644 --- a/src/test/ui/async-await/async-await-let-else.drop-tracking.stderr +++ b/src/test/ui/async-await/async-await-let-else.drop-tracking.stderr @@ -40,7 +40,7 @@ LL | async fn bar2(_: T) -> ! { LL | | panic!() LL | | } | |_^ - = note: required because it captures the following types: `ResumeTy`, `Option`, `impl Future`, `()` + = note: required because it captures the following types: `&mut Context<'_>`, `Option`, `impl Future`, `()` note: required because it's used within this `async fn` body --> $DIR/async-await-let-else.rs:21:32 | diff --git a/src/test/ui/async-await/issue-68112.drop_tracking.stderr b/src/test/ui/async-await/issue-68112.drop_tracking.stderr index f2802698fd5b6..1c90bedae790c 100644 --- a/src/test/ui/async-await/issue-68112.drop_tracking.stderr +++ b/src/test/ui/async-await/issue-68112.drop_tracking.stderr @@ -57,7 +57,7 @@ note: required because it appears within the type `impl Future impl Future>> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - = note: required because it captures the following types: `ResumeTy`, `impl Future>>`, `()`, `Ready` + = note: required because it captures the following types: `&mut Context<'_>`, `impl Future>>`, `()`, `Ready` note: required because it's used within this `async` block --> $DIR/issue-68112.rs:60:20 | diff --git a/src/test/ui/async-await/issue-68112.no_drop_tracking.stderr b/src/test/ui/async-await/issue-68112.no_drop_tracking.stderr index 38eb85b302fd5..e09ae7fedd805 100644 --- a/src/test/ui/async-await/issue-68112.no_drop_tracking.stderr +++ b/src/test/ui/async-await/issue-68112.no_drop_tracking.stderr @@ -57,7 +57,7 @@ note: required because it appears within the type `impl Future impl Future>> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - = note: required because it captures the following types: `ResumeTy`, `impl Future>>`, `()`, `i32`, `Ready` + = note: required because it captures the following types: `&mut Context<'_>`, `impl Future>>`, `()`, `i32`, `Ready` note: required because it's used within this `async` block --> $DIR/issue-68112.rs:60:20 | diff --git a/src/test/ui/async-await/issue-69446-fnmut-capture.stderr b/src/test/ui/async-await/issue-69446-fnmut-capture.stderr index 3d2b0402bc52c..e6ad2f0d444bb 100644 --- a/src/test/ui/async-await/issue-69446-fnmut-capture.stderr +++ b/src/test/ui/async-await/issue-69446-fnmut-capture.stderr @@ -14,6 +14,9 @@ LL | | }); | = note: `FnMut` closures only have access to their captured variables while they are executing... = note: ...therefore, they cannot allow references to captured variables to escape + = note: requirement occurs because of a mutable reference to `Context<'_>` + = note: mutable references are invariant over their type parameter + = help: see for more information about variance error: aborting due to previous error diff --git a/src/test/ui/async-await/issue-70935-complex-spans.drop_tracking.stderr b/src/test/ui/async-await/issue-70935-complex-spans.drop_tracking.stderr index 721234aa4a782..a8fd97cde8f7a 100644 --- a/src/test/ui/async-await/issue-70935-complex-spans.drop_tracking.stderr +++ b/src/test/ui/async-await/issue-70935-complex-spans.drop_tracking.stderr @@ -18,7 +18,7 @@ LL | async fn baz(_c: impl FnMut() -> T) where T: Future { | ___________________________________________________________________^ LL | | } | |_^ - = note: required because it captures the following types: `ResumeTy`, `impl Future`, `()` + = note: required because it captures the following types: `&mut Context<'_>`, `impl Future`, `()` note: required because it's used within this `async` block --> $DIR/issue-70935-complex-spans.rs:16:5 | diff --git a/src/test/ui/async-await/partial-drop-partial-reinit.drop_tracking.stderr b/src/test/ui/async-await/partial-drop-partial-reinit.drop_tracking.stderr index 17b4ef7bdc671..25876d5084015 100644 --- a/src/test/ui/async-await/partial-drop-partial-reinit.drop_tracking.stderr +++ b/src/test/ui/async-await/partial-drop-partial-reinit.drop_tracking.stderr @@ -11,7 +11,7 @@ LL | async fn foo() { | = help: within `impl Future`, the trait `Send` is not implemented for `NotSend` = note: required because it appears within the type `(NotSend,)` - = note: required because it captures the following types: `ResumeTy`, `(NotSend,)`, `()`, `impl Future` + = note: required because it captures the following types: `&mut Context<'_>`, `(NotSend,)`, `()`, `impl Future` note: required because it's used within this `async fn` body --> $DIR/partial-drop-partial-reinit.rs:31:16 | diff --git a/src/test/ui/async-await/partial-drop-partial-reinit.no_drop_tracking.stderr b/src/test/ui/async-await/partial-drop-partial-reinit.no_drop_tracking.stderr index 34d8a159f1064..dba2a620779f0 100644 --- a/src/test/ui/async-await/partial-drop-partial-reinit.no_drop_tracking.stderr +++ b/src/test/ui/async-await/partial-drop-partial-reinit.no_drop_tracking.stderr @@ -11,7 +11,7 @@ LL | async fn foo() { | = help: within `impl Future`, the trait `Send` is not implemented for `NotSend` = note: required because it appears within the type `(NotSend,)` - = note: required because it captures the following types: `ResumeTy`, `(NotSend,)`, `impl Future`, `()` + = note: required because it captures the following types: `&mut Context<'_>`, `(NotSend,)`, `impl Future`, `()` note: required because it's used within this `async fn` body --> $DIR/partial-drop-partial-reinit.rs:31:16 | diff --git a/src/test/ui/regions/closure-in-projection-issue-97405.rs b/src/test/ui/regions/closure-in-projection-issue-97405.rs index e567d5c2723f2..88b1c1396516d 100644 --- a/src/test/ui/regions/closure-in-projection-issue-97405.rs +++ b/src/test/ui/regions/closure-in-projection-issue-97405.rs @@ -22,11 +22,11 @@ fn good_generic_fn() { // This should fail because `T` ends up in the upvars of the closure. fn bad_generic_fn(t: T) { assert_static(opaque(async move { t; }).next()); - //~^ ERROR the associated type `::Item` may not live long enough + //~^ ERROR the parameter type `T` may not live long enough assert_static(opaque(move || { t; }).next()); //~^ ERROR the associated type `::Item` may not live long enough assert_static(opaque(opaque(async move { t; }).next()).next()); - //~^ ERROR the associated type `::Item` may not live long enough + //~^ ERROR the parameter type `T` may not live long enough } fn main() {} diff --git a/src/test/ui/regions/closure-in-projection-issue-97405.stderr b/src/test/ui/regions/closure-in-projection-issue-97405.stderr index c08f1059ebf58..907964aaf379e 100644 --- a/src/test/ui/regions/closure-in-projection-issue-97405.stderr +++ b/src/test/ui/regions/closure-in-projection-issue-97405.stderr @@ -1,11 +1,13 @@ -error[E0310]: the associated type `::Item` may not live long enough +error[E0310]: the parameter type `T` may not live long enough --> $DIR/closure-in-projection-issue-97405.rs:24:5 | LL | assert_static(opaque(async move { t; }).next()); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds | - = help: consider adding an explicit lifetime bound `::Item: 'static`... - = note: ...so that the type `::Item` will meet its required lifetime bounds +help: consider adding an explicit lifetime bound... + | +LL | fn bad_generic_fn(t: T) { + | +++++++++ error[E0310]: the associated type `::Item` may not live long enough --> $DIR/closure-in-projection-issue-97405.rs:26:5 @@ -16,14 +18,16 @@ LL | assert_static(opaque(move || { t; }).next()); = help: consider adding an explicit lifetime bound `::Item: 'static`... = note: ...so that the type `::Item` will meet its required lifetime bounds -error[E0310]: the associated type `::Item` may not live long enough +error[E0310]: the parameter type `T` may not live long enough --> $DIR/closure-in-projection-issue-97405.rs:28:5 | LL | assert_static(opaque(opaque(async move { t; }).next()).next()); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds | - = help: consider adding an explicit lifetime bound `::Item: 'static`... - = note: ...so that the type `::Item` will meet its required lifetime bounds +help: consider adding an explicit lifetime bound... + | +LL | fn bad_generic_fn(t: T) { + | +++++++++ error: aborting due to 3 previous errors