Rollup merge of #105915 - andrewpollack:revert-105250-async-rm-resumety, r=tmandry

Revert "Replace usage of `ResumeTy` in async lowering with `Context`"

Reverts #105250
Fixes: #105501

Following instructions from [forge](https://forge.rust-lang.org/compiler/reviews.html#reverts).

This change introduced a breaking change that is not actionable nor relevant, and is blocking updates to our toolchain. Along with other comments on the CL marking issues that are fixed by reverts, reverting is best until these issues can be resolved

cc. `@Swatinem`

Author: matthiaskrgr

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::{kw, sym, Ident};
+use rustc_span::symbol::{sym, Ident};
 use rustc_span::DUMMY_SP;
 use thin_vec::thin_vec;
 
@@ -596,38 +596,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> hir::ExprKind<'hir> {
         let output = ret_ty.unwrap_or_else(|| hir::FnRetTy::DefaultReturn(self.lower_span(span)));
 
-        // 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 <https://github.com/rust-lang/rust/issues/68923>.
-        // 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,
-        };
+        // 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);
         let input_ty = hir::Ty {
             hir_id: self.next_id(),
-            kind: hir::TyKind::Rptr(context_lifetime, context_ty),
-            span: self.lower_span(span),
+            kind: hir::TyKind::Path(resume_ty),
+            span: unstable_span,
         };
 
         // The closure/generator `FnDecl` takes a single (resume) argument of type `input_ty`.
@@ -686,9 +662,12 @@ 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 {
@@ -731,7 +710,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ///     mut __awaitee => loop {
     ///         match unsafe { ::std::future::Future::poll(
     ///             <::std::pin::Pin>::new_unchecked(&mut __awaitee),
-    ///             task_context,
+    ///             ::std::future::get_context(task_context),
     ///         ) } {
     ///             ::std::task::Poll::Ready(result) => break result,
     ///             ::std::task::Poll::Pending => {}
@@ -772,7 +751,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // unsafe {
         //     ::std::future::Future::poll(
         //         ::std::pin::Pin::new_unchecked(&mut __awaitee),
-        //         task_context,
+        //         ::std::future::get_context(task_context),
         //     )
         // }
         let poll_expr = {
@@ -790,10 +769,16 @@ 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, task_context],
+                arena_vec![self; new_unchecked, get_context],
                 Some(expr_hir_id),
             );
             self.arena.alloc(self.expr_unsafe(call))

compiler/rustc_hir/src/lang_items.rs

@@ -286,9 +286,10 @@ 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;

compiler/rustc_span/src/symbol.rs

@@ -164,7 +164,6 @@ symbols! {
         Capture,
         Center,
         Clone,
-        Context,
         Continue,
         Copy,
         Count,
@@ -264,6 +263,7 @@ symbols! {
         Relaxed,
         Release,
         Result,
+        ResumeTy,
         Return,
         Right,
         Rust,
@@ -753,6 +753,7 @@ symbols! {
         generic_associated_types_extended,
         generic_const_exprs,
         generic_param_attrs,
+        get_context,
         global_allocator,
         global_asm,
         globs,

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`.
-// FIXME(swatinem): This type can be removed when bumping the bootstrap compiler
+#[cfg_attr(not(bootstrap), lang = "ResumeTy")]
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]
 #[derive(Debug, Copy, Clone)]
@@ -61,7 +61,6 @@ 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")]
@@ -103,8 +102,7 @@ where
     GenFuture(gen)
 }
 
-// FIXME(swatinem): This fn can be removed when bumping the bootstrap compiler
-#[cfg_attr(bootstrap, lang = "get_context")]
+#[lang = "get_context"]
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]
 #[must_use]
@@ -115,10 +113,6 @@ 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
-// <https://github.com/rust-lang/rust/issues/104826>.
 #[cfg_attr(not(bootstrap), lang = "identity_future")]
 #[doc(hidden)]
 #[unstable(feature = "gen_future", issue = "50547")]

library/core/src/task/wake.rs

@@ -174,7 +174,6 @@ 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

src/test/ui/async-await/async-await-let-else.drop-tracking.stderr

@@ -40,7 +40,7 @@ LL |   async fn bar2<T>(_: T) -> ! {
 LL | |     panic!()
 LL | | }
    | |_^
-   = note: required because it captures the following types: `&mut Context<'_>`, `Option<bool>`, `impl Future<Output = !>`, `()`
+   = note: required because it captures the following types: `ResumeTy`, `Option<bool>`, `impl Future<Output = !>`, `()`
 note: required because it's used within this `async fn` body
   --> $DIR/async-await-let-else.rs:21:32
    |

src/test/ui/async-await/issue-68112.drop_tracking.stderr

@@ -57,7 +57,7 @@ note: required because it appears within the type `impl Future<Output = Arc<RefC
    |
 LL | fn make_non_send_future2() -> impl Future<Output = Arc<RefCell<i32>>> {
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: required because it captures the following types: `&mut Context<'_>`, `impl Future<Output = Arc<RefCell<i32>>>`, `()`, `Ready<i32>`
+   = note: required because it captures the following types: `ResumeTy`, `impl Future<Output = Arc<RefCell<i32>>>`, `()`, `Ready<i32>`
 note: required because it's used within this `async` block
   --> $DIR/issue-68112.rs:60:20
    |

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<Output = Arc<RefC
    |
 LL | fn make_non_send_future2() -> impl Future<Output = Arc<RefCell<i32>>> {
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: required because it captures the following types: `&mut Context<'_>`, `impl Future<Output = Arc<RefCell<i32>>>`, `()`, `i32`, `Ready<i32>`
+   = note: required because it captures the following types: `ResumeTy`, `impl Future<Output = Arc<RefCell<i32>>>`, `()`, `i32`, `Ready<i32>`
 note: required because it's used within this `async` block
   --> $DIR/issue-68112.rs:60:20
    |

src/test/ui/async-await/issue-69446-fnmut-capture.stderr

@@ -14,9 +14,6 @@ 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 <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
 error: aborting due to previous error
 

src/test/ui/async-await/issue-70935-complex-spans.drop_tracking.stderr

@@ -18,7 +18,7 @@ LL |   async fn baz<T>(_c: impl FnMut() -> T) where T: Future<Output=()> {
    |  ___________________________________________________________________^
 LL | | }
    | |_^
-   = note: required because it captures the following types: `&mut Context<'_>`, `impl Future<Output = ()>`, `()`
+   = note: required because it captures the following types: `ResumeTy`, `impl Future<Output = ()>`, `()`
 note: required because it's used within this `async` block
   --> $DIR/issue-70935-complex-spans.rs:16:5
    |

src/test/ui/async-await/partial-drop-partial-reinit.drop_tracking.stderr

@@ -11,7 +11,7 @@ LL | async fn foo() {
    |
    = help: within `impl Future<Output = ()>`, 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: `&mut Context<'_>`, `(NotSend,)`, `()`, `impl Future<Output = ()>`
+   = note: required because it captures the following types: `ResumeTy`, `(NotSend,)`, `()`, `impl Future<Output = ()>`
 note: required because it's used within this `async fn` body
   --> $DIR/partial-drop-partial-reinit.rs:31:16
    |

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<Output = ()>`, 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: `&mut Context<'_>`, `(NotSend,)`, `impl Future<Output = ()>`, `()`
+   = note: required because it captures the following types: `ResumeTy`, `(NotSend,)`, `impl Future<Output = ()>`, `()`
 note: required because it's used within this `async fn` body
   --> $DIR/partial-drop-partial-reinit.rs:31:16
    |

src/test/ui/regions/closure-in-projection-issue-97405.rs

@@ -22,11 +22,11 @@ fn good_generic_fn<T>() {
 // This should fail because `T` ends up in the upvars of the closure.
 fn bad_generic_fn<T: Copy>(t: T) {
     assert_static(opaque(async move { t; }).next());
-    //~^ ERROR the parameter type `T` may not live long enough
+    //~^ ERROR the associated type `<impl Iterator as Iterator>::Item` may not live long enough
     assert_static(opaque(move || { t; }).next());
     //~^ ERROR the associated type `<impl Iterator as Iterator>::Item` may not live long enough
     assert_static(opaque(opaque(async move { t; }).next()).next());
-    //~^ ERROR the parameter type `T` may not live long enough
+    //~^ ERROR the associated type `<impl Iterator as Iterator>::Item` may not live long enough
 }
 
 fn main() {}

src/test/ui/regions/closure-in-projection-issue-97405.stderr

@@ -1,13 +1,11 @@
-error[E0310]: the parameter type `T` may not live long enough
+error[E0310]: the associated type `<impl Iterator as Iterator>::Item` 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...
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-LL | fn bad_generic_fn<T: Copy + 'static>(t: T) {
-   |                           +++++++++
+   = help: consider adding an explicit lifetime bound `<impl Iterator as Iterator>::Item: 'static`...
+   = note: ...so that the type `<impl Iterator as Iterator>::Item` will meet its required lifetime bounds
 
 error[E0310]: the associated type `<impl Iterator as Iterator>::Item` may not live long enough
   --> $DIR/closure-in-projection-issue-97405.rs:26:5
@@ -18,16 +16,14 @@ LL |     assert_static(opaque(move || { t; }).next());
    = help: consider adding an explicit lifetime bound `<impl Iterator as Iterator>::Item: 'static`...
    = note: ...so that the type `<impl Iterator as Iterator>::Item` will meet its required lifetime bounds
 
-error[E0310]: the parameter type `T` may not live long enough
+error[E0310]: the associated type `<impl Iterator as Iterator>::Item` 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...
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-LL | fn bad_generic_fn<T: Copy + 'static>(t: T) {
-   |                           +++++++++
+   = help: consider adding an explicit lifetime bound `<impl Iterator as Iterator>::Item: 'static`...
+   = note: ...so that the type `<impl Iterator as Iterator>::Item` will meet its required lifetime bounds
 
 error: aborting due to 3 previous errors