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Replace usage of ResumeTy in async lowering with Context

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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.
This commit is contained in:
Arpad Borsos 2022-12-04 12:32:15 +01:00 • committed by Arpad Borsos
parent ed61c139c2
commit cf031a3355
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GPG key ID: 570F20163159CB55
14 changed files with 70 additions and 43 deletions
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57
compiler/rustc_ast_lowering/src/expr.rs
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@ -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 <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,
};
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))