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Rollup merge of #121654 - compiler-errors:async-fn-for-fn-def, r=oli-obk

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Fix `async Fn` confirmation for `FnDef`/`FnPtr`/`Closure` types

Fixes three issues:
1. The code in `extract_tupled_inputs_and_output_from_async_callable` was accidentally getting the *future* type and the *output* type (returned by the future) messed up for fnptr/fndef/closure types. :/
2. We have a (class of) bug(s) in the old solver where we don't really support higher ranked built-in `Future` goals for generators. This is not possible to hit on stable code, but [can be hit with `unboxed_closures`](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=e935de7181e37e13515ad01720bcb899) (#121653).
    * I'm opting not to fix that in this PR. Instead, I just instantiate placeholders when confirming `async Fn` goals.
4. Fixed a bug when generating `FnPtr` shims for `async Fn` trait goals.

r? oli-obk
This commit is contained in:
Guillaume Gomez
2024-02-29 14:33:50 +01:00
committed by GitHub
parent 1ee54538a3 c8e3f35eb6
commit 5978b6ff83
12 changed files with 330 additions and 104 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"),