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

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

Reverts rust-lang/rust#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`

1 files changed, 21 insertions, 36 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index e86e807279d..a3f5c18f2e7 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::{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))