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Actually, stop making any assumption about the projections applied to the upvar

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This commit is contained in:
Michael Goulet 2024-04-08 19:47:37 -04:00
parent ab5bda1aa7
commit 54a93ab11e
2 changed files with 34 additions and 19 deletions
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36
compiler/rustc_mir_transform/src/coroutine/by_move_body.rs
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@ -281,14 +281,14 @@ impl<'tcx> MutVisitor<'tcx> for MakeByMoveBody<'tcx> {
if place.local == ty::CAPTURE_STRUCT_LOCAL
&& let Some((&mir::ProjectionElem::Field(idx, _), projection)) =
place.projection.split_first()
&& let Some(&(remapped_idx, remapped_ty, needs_deref, additional_projections)) =
&& let Some(&(remapped_idx, remapped_ty, needs_deref, bridging_projections)) =
self.field_remapping.get(&idx)
{
// As noted before, if the parent closure captures a field by value, and
// the child captures a field by ref, then for the by-move body we're
// generating, we also are taking that field by value. Peel off a deref,
// since a layer of reffing has now become redundant.
let final_deref = if needs_deref {
// since a layer of ref'ing has now become redundant.
let final_projections = if needs_deref {
let Some((mir::ProjectionElem::Deref, projection)) = projection.split_first()
else {
bug!(
@ -302,20 +302,18 @@ impl<'tcx> MutVisitor<'tcx> for MakeByMoveBody<'tcx> {
projection
};
// The only thing that should be left is a deref, if the parent captured
// an upvar by-ref.
std::assert_matches::assert_matches!(final_deref, [] | [mir::ProjectionElem::Deref]);
// For all of the additional projections that come out of precise capturing,
// re-apply these projections.
let additional_projections =
additional_projections.iter().map(|elem| match elem.kind {
ProjectionKind::Deref => mir::ProjectionElem::Deref,
ProjectionKind::Field(idx, VariantIdx::ZERO) => {
mir::ProjectionElem::Field(idx, elem.ty)
}
_ => unreachable!("precise captures only through fields and derefs"),
});
// These projections are applied in order to "bridge" the local that we are
// currently transforming *from* the old upvar that the by-ref coroutine used
// to capture *to* the upvar of the parent coroutine-closure. For example, if
// the parent captures `&s` but the child captures `&(s.field)`, then we will
// apply a field projection.
let bridging_projections = bridging_projections.iter().map(|elem| match elem.kind {
ProjectionKind::Deref => mir::ProjectionElem::Deref,
ProjectionKind::Field(idx, VariantIdx::ZERO) => {
mir::ProjectionElem::Field(idx, elem.ty)
}
_ => unreachable!("precise captures only through fields and derefs"),
});
// We start out with an adjusted field index (and ty), representing the
// upvar that we get from our parent closure. We apply any of the additional
@ -326,8 +324,8 @@ impl<'tcx> MutVisitor<'tcx> for MakeByMoveBody<'tcx> {
projection: self.tcx.mk_place_elems_from_iter(
[mir::ProjectionElem::Field(remapped_idx, remapped_ty)]
.into_iter()
.chain(additional_projections)
.chain(final_deref.iter().copied()),
.chain(bridging_projections)
.chain(final_projections.iter().copied()),
),
};
}

17
tests/ui/async-await/async-closures/truncated-fields-when-imm.rs Normal file
View File

@ -0,0 +1,17 @@
//@ edition: 2021
//@ check-pass
#![feature(async_closure)]
pub struct Struct {
pub path: String,
}
// In `upvar.rs`, `truncate_capture_for_optimization` means that we don't actually
// capture `&(*s.path)` here, but instead just `&(*s)`, but ONLY when the upvar is
// immutable. This means that the assumption we have in `ByMoveBody` pass is wrong.
pub fn test(s: &Struct) {
let c = async move || { let path = &s.path; };
}
fn main() {}