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Don't emit higher-ranked Future obligations when confirm async Fn goals

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This commit is contained in:
Michael Goulet 2024-02-26 22:49:20 +00:00
parent 118730b9a3
commit 4c0016a01f
1 changed files with 16 additions and 6 deletions
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22
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
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@ -923,14 +923,22 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
[self_ty, Ty::new_tup(tcx, sig.inputs())],
)
});
// We must additionally check that the return type impls `Future`.
// FIXME(async_closures): Investigate this before stabilization.
// We instantiate this binder eagerly because the `confirm_future_candidate`
// method doesn't support higher-ranked futures, which the `AsyncFn`
// traits expressly allow the user to write. To fix this correctly,
// we'd need to instantiate trait bounds before we get to selection,
// like the new trait solver does.
let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
let placeholder_output_ty = self.infcx.enter_forall_and_leak_universe(sig.output());
nested.push(obligation.with(
tcx,
sig.map_bound(|sig| {
ty::TraitRef::new(tcx, future_trait_def_id, [sig.output()])
}),
ty::TraitRef::new(tcx, future_trait_def_id, [placeholder_output_ty]),
));
(trait_ref, Ty::from_closure_kind(tcx, ty::ClosureKind::Fn))
}
ty::Closure(_, args) => {
@ -943,14 +951,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
[self_ty, sig.inputs()[0]],
)
});
// We must additionally check that the return type impls `Future`.
// See FIXME in last branch for why we instantiate the binder eagerly.
let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
let placeholder_output_ty = self.infcx.enter_forall_and_leak_universe(sig.output());
nested.push(obligation.with(
tcx,
sig.map_bound(|sig| {
ty::TraitRef::new(tcx, future_trait_def_id, [sig.output()])
}),
ty::TraitRef::new(tcx, future_trait_def_id, [placeholder_output_ty]),
));
(trait_ref, args.kind_ty())
}
_ => bug!("expected callable type for AsyncFn candidate"),