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Force move async-closures that are FnOnce to make their inner coroutines also move

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This commit is contained in:
Michael Goulet
2024-04-03 12:16:17 -04:00
parent 3d9d5d7c96
commit 55e46612c1
7 changed files with 57 additions and 73 deletions
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24
compiler/rustc_hir_typeck/src/upvar.rs
View File

@@ -166,7 +166,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
span: Span,
body_id: hir::BodyId,
body: &'tcx hir::Body<'tcx>,
capture_clause: hir::CaptureBy,
mut capture_clause: hir::CaptureBy,
) {
// Extract the type of the closure.
let ty = self.node_ty(closure_hir_id);
@@ -259,6 +259,28 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
)
.consume_body(body);
// If a coroutine is comes from a coroutine-closure that is `move`, but
// the coroutine-closure was inferred to be `FnOnce` during signature
// inference, then it's still possible that we try to borrow upvars from
// the coroutine-closure because they are not used by the coroutine body
// in a way that forces a move.
//
// This would lead to an impossible to satisfy situation, since `AsyncFnOnce`
// coroutine bodies can't borrow from their parent closure. To fix this,
// we force the inner coroutine to also be `move`. This only matters for
// coroutine-closures that are `move` since otherwise they themselves will
// be borrowing from the outer environment, so there's no self-borrows occuring.
if let UpvarArgs::Coroutine(..) = args
&& let hir::CoroutineKind::Desugared(_, hir::CoroutineSource::Closure) =
self.tcx.coroutine_kind(closure_def_id).expect("coroutine should have kind")
&& let parent_hir_id =
self.tcx.local_def_id_to_hir_id(self.tcx.local_parent(closure_def_id))
&& let parent_ty = self.node_ty(parent_hir_id)
&& let Some(ty::ClosureKind::FnOnce) = self.closure_kind(parent_ty)
{
capture_clause = self.tcx.hir_node(parent_hir_id).expect_closure().capture_clause;
}
debug!(
"For closure={:?}, capture_information={:#?}",
closure_def_id, delegate.capture_information

20
compiler/rustc_mir_transform/src/coroutine/by_move_body.rs
View File

@@ -91,15 +91,17 @@ impl<'tcx> MirPass<'tcx> for ByMoveBody {
return;
}
let ty::Coroutine(_, coroutine_args) = *coroutine_ty.kind() else { bug!("{body:#?}") };
// We don't need to generate a by-move coroutine if the kind of the coroutine is
// already `FnOnce` -- that means that any upvars that the closure consumes have
// already been taken by-value.
let coroutine_kind = coroutine_args.as_coroutine().kind_ty().to_opt_closure_kind().unwrap();
if coroutine_kind == ty::ClosureKind::FnOnce {
// We don't need to generate a by-move coroutine if the coroutine body was
// produced by the `CoroutineKindShim`, since it's already by-move.
if matches!(body.source.instance, ty::InstanceDef::CoroutineKindShim { .. }) {
return;
}
let ty::Coroutine(_, args) = *coroutine_ty.kind() else { bug!("{body:#?}") };
let args = args.as_coroutine();
let coroutine_kind = args.kind_ty().to_opt_closure_kind().unwrap();
let parent_def_id = tcx.local_parent(coroutine_def_id);
let ty::CoroutineClosure(_, parent_args) =
*tcx.type_of(parent_def_id).instantiate_identity().kind()
@@ -128,6 +130,12 @@ impl<'tcx> MirPass<'tcx> for ByMoveBody {
// the outer closure body -- we need to change the coroutine to take the
// upvar by value.
if coroutine_capture.is_by_ref() && !parent_capture.is_by_ref() {
assert_ne!(
coroutine_kind,
ty::ClosureKind::FnOnce,
"`FnOnce` coroutine-closures return coroutines that capture from \
their body; it will always result in a borrowck error!"
);
by_ref_fields.insert(FieldIdx::from_usize(num_args + idx));
}