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async: Give predictable, reserved name to binding generated from .await expressions.

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This name makes it to debuginfo and allows debuggers to identify such bindings and
their captured versions in suspended async fns.
This commit is contained in:
Michael Woerister 2022-03-16 15:52:21 +01:00
parent 461e807801
commit 78e27e2c7a
3 changed files with 40 additions and 14 deletions
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29
compiler/rustc_ast_lowering/src/expr.rs
View File

@ -618,9 +618,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
/// Desugar `<expr>.await` into:
/// ```rust
/// match ::std::future::IntoFuture::into_future(<expr>) {
/// mut pinned => loop {
/// mut __awaitee => loop {
/// match unsafe { ::std::future::Future::poll(
/// <::std::pin::Pin>::new_unchecked(&mut pinned),
/// <::std::pin::Pin>::new_unchecked(&mut __awaitee),
/// ::std::future::get_context(task_context),
/// ) } {
/// ::std::task::Poll::Ready(result) => break result,
@ -657,21 +657,24 @@ impl<'hir> LoweringContext<'_, 'hir> {
let expr = self.lower_expr_mut(expr);
let expr_hir_id = expr.hir_id;
let pinned_ident = Ident::with_dummy_span(sym::pinned);
let (pinned_pat, pinned_pat_hid) =
self.pat_ident_binding_mode(span, pinned_ident, hir::BindingAnnotation::Mutable);
// Note that the name of this binding must not be changed to something else because
// debuggers and debugger extensions expect it to be called `__awaitee`. They use
// this name to identify what is being awaited by a suspended async functions.
let awaitee_ident = Ident::with_dummy_span(sym::__awaitee);
let (awaitee_pat, awaitee_pat_hid) =
self.pat_ident_binding_mode(span, awaitee_ident, hir::BindingAnnotation::Mutable);
let task_context_ident = Ident::with_dummy_span(sym::_task_context);
// unsafe {
// ::std::future::Future::poll(
// ::std::pin::Pin::new_unchecked(&mut pinned),
// ::std::pin::Pin::new_unchecked(&mut __awaitee),
// ::std::future::get_context(task_context),
// )
// }
let poll_expr = {
let pinned = self.expr_ident(span, pinned_ident, pinned_pat_hid);
let ref_mut_pinned = self.expr_mut_addr_of(span, pinned);
let awaitee = self.expr_ident(span, awaitee_ident, awaitee_pat_hid);
let ref_mut_awaitee = self.expr_mut_addr_of(span, awaitee);
let task_context = if let Some(task_context_hid) = self.task_context {
self.expr_ident_mut(span, task_context_ident, task_context_hid)
} else {
@ -681,7 +684,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
let new_unchecked = self.expr_call_lang_item_fn_mut(
span,
hir::LangItem::PinNewUnchecked,
arena_vec![self; ref_mut_pinned],
arena_vec![self; ref_mut_awaitee],
Some(expr_hir_id),
);
let get_context = self.expr_call_lang_item_fn_mut(
@ -782,8 +785,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
span: self.lower_span(span),
});
// mut pinned => loop { ... }
let pinned_arm = self.arm(pinned_pat, loop_expr);
// mut __awaitee => loop { ... }
let awaitee_arm = self.arm(awaitee_pat, loop_expr);
// `match ::std::future::IntoFuture::into_future(<expr>) { ... }`
let into_future_span = self.mark_span_with_reason(
@ -799,11 +802,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
);
// match <into_future_expr> {
// mut pinned => loop { .. }
// mut __awaitee => loop { .. }
// }
hir::ExprKind::Match(
into_future_expr,
arena_vec![self; pinned_arm],
arena_vec![self; awaitee_arm],
hir::MatchSource::AwaitDesugar,
)
}

2
compiler/rustc_span/src/symbol.rs
View File

@ -272,6 +272,7 @@ symbols! {
__D,
__H,
__S,
__awaitee,
__try_var,
_d,
_e,
@ -1022,7 +1023,6 @@ symbols! {
pattern_parentheses,
phantom_data,
pin,
pinned,
platform_intrinsics,
plugin,
plugin_registrar,

23
src/test/codegen/async-fn-debug-awaitee-field.rs Normal file
View File

@ -0,0 +1,23 @@
// This test makes sure that the generator field capturing the awaitee in a `.await` expression
// is called "__awaitee" in debuginfo. This name must not be changed since debuggers and debugger
// extensions rely on the field having this name.
// ignore-tidy-linelength
// compile-flags: -C debuginfo=2 --edition=2018
async fn foo() {}
async fn async_fn_test() {
foo().await;
}
// NONMSVC: [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_structure_type, name: "{async_fn_env#0}",
// MSVC: [[GEN:!.*]] = !DICompositeType(tag: DW_TAG_union_type, name: "enum$<async_fn_debug_awaitee_field::async_fn_test::async_fn_env$0>",
// CHECK: [[SUSPEND_STRUCT:!.*]] = !DICompositeType(tag: DW_TAG_structure_type, name: "Suspend0", scope: [[GEN]],
// CHECK: !DIDerivedType(tag: DW_TAG_member, name: "__awaitee", scope: [[SUSPEND_STRUCT]], {{.*}}, baseType: [[AWAITEE_TYPE:![0-9]*]],
// NONMSVC: [[AWAITEE_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "GenFuture<async_fn_debug_awaitee_field::foo::{async_fn_env#0}>",
// MSVC: [[AWAITEE_TYPE]] = !DICompositeType(tag: DW_TAG_structure_type, name: "GenFuture<enum$<async_fn_debug_awaitee_field::foo::async_fn_env$0> >",
fn main() {
let _fn = async_fn_test();
}