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Rollup merge of #109545 - compiler-errors:rpitit-wf, r=eholk

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Deeply check well-formedness of return-position `impl Trait` in trait

Walk the bounds of RPITITs to see if we find any more RPITITs 😸
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Matthias Krüger 2023-03-25 03:37:12 +01:00 • committed by GitHub
commit 3b49ad3814
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4 changed files with 108 additions and 44 deletions
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105
compiler/rustc_hir_analysis/src/check/wfcheck.rs
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@ -1544,42 +1544,81 @@ fn check_return_position_impl_trait_in_trait_bounds<'tcx>(
span: Span,
) {
let tcx = wfcx.tcx();
if let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id())
&& assoc_item.container == ty::AssocItemContainer::TraitContainer
{
// FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty): Even with the new lowering
// strategy, we can't just call `check_associated_item` on the new RPITITs,
// because tests like `tests/ui/async-await/in-trait/implied-bounds.rs` will fail.
// That's because we need to check that the bounds of the RPITIT hold using
// the special substs that we create during opaque type lowering, otherwise we're
// getting a bunch of early bound and free regions mixed up... Haven't looked too
// deep into this, though.
for arg in fn_output.walk() {
if let ty::GenericArgKind::Type(ty) = arg.unpack()
// RPITITs are always eagerly normalized into opaques, so always look for an
// opaque here.
&& let ty::Alias(ty::Opaque, opaque_ty) = ty.kind()
&& let Some(opaque_def_id) = opaque_ty.def_id.as_local()
&& let opaque = tcx.hir().expect_item(opaque_def_id).expect_opaque_ty()
&& let hir::OpaqueTyOrigin::FnReturn(source) | hir::OpaqueTyOrigin::AsyncFn(source) = opaque.origin
&& source == fn_def_id
let Some(assoc_item) = tcx.opt_associated_item(fn_def_id.to_def_id()) else {
return;
};
if assoc_item.container != ty::AssocItemContainer::TraitContainer {
return;
}
fn_output.visit_with(&mut ImplTraitInTraitFinder {
wfcx,
fn_def_id,
depth: ty::INNERMOST,
seen: FxHashSet::default(),
});
}
// FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty): Even with the new lowering
// strategy, we can't just call `check_associated_item` on the new RPITITs,
// because tests like `tests/ui/async-await/in-trait/implied-bounds.rs` will fail.
// That's because we need to check that the bounds of the RPITIT hold using
// the special substs that we create during opaque type lowering, otherwise we're
// getting a bunch of early bound and free regions mixed up... Haven't looked too
// deep into this, though.
struct ImplTraitInTraitFinder<'a, 'tcx> {
wfcx: &'a WfCheckingCtxt<'a, 'tcx>,
fn_def_id: LocalDefId,
depth: ty::DebruijnIndex,
seen: FxHashSet<DefId>,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ImplTraitInTraitFinder<'_, 'tcx> {
type BreakTy = !;
fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<!> {
let tcx = self.wfcx.tcx();
if let ty::Alias(ty::Opaque, unshifted_opaque_ty) = *ty.kind()
&& self.seen.insert(unshifted_opaque_ty.def_id)
&& let Some(opaque_def_id) = unshifted_opaque_ty.def_id.as_local()
&& let opaque = tcx.hir().expect_item(opaque_def_id).expect_opaque_ty()
&& let hir::OpaqueTyOrigin::FnReturn(source) | hir::OpaqueTyOrigin::AsyncFn(source) = opaque.origin
&& source == self.fn_def_id
{
let opaque_ty = tcx.fold_regions(unshifted_opaque_ty, |re, depth| {
if let ty::ReLateBound(index, bv) = re.kind() {
if depth != ty::INNERMOST {
return tcx.mk_re_error_with_message(
DUMMY_SP,
"we shouldn't walk non-predicate binders with `impl Trait`...",
);
}
tcx.mk_re_late_bound(index.shifted_out_to_binder(self.depth), bv)
} else {
re
}
});
for (bound, bound_span) in tcx
.bound_explicit_item_bounds(opaque_ty.def_id)
.subst_iter_copied(tcx, opaque_ty.substs)
{
let span = tcx.def_span(opaque_ty.def_id);
let bounds = wfcx.tcx().explicit_item_bounds(opaque_ty.def_id);
let wf_obligations = bounds.iter().flat_map(|&(bound, bound_span)| {
let bound = ty::EarlyBinder(bound).subst(tcx, opaque_ty.substs);
let normalized_bound = wfcx.normalize(span, None, bound);
traits::wf::predicate_obligations(
wfcx.infcx,
wfcx.param_env,
wfcx.body_def_id,
normalized_bound,
bound_span,
)
});
wfcx.register_obligations(wf_obligations);
let bound = self.wfcx.normalize(bound_span, None, bound);
self.wfcx.register_obligations(traits::wf::predicate_obligations(
self.wfcx.infcx,
self.wfcx.param_env,
self.wfcx.body_def_id,
bound,
bound_span,
));
// Set the debruijn index back to innermost here, since we already eagerly
// shifted the substs that we use to generate these bounds. This is unfortunately
// subtly different behavior than the `ImplTraitInTraitFinder` we use in `param_env`,
// but that function doesn't actually need to normalize the bound it's visiting
// (whereas we have to do so here)...
let old_depth = std::mem::replace(&mut self.depth, ty::INNERMOST);
bound.visit_with(self);
self.depth = old_depth;
}
}
ty.super_visit_with(self)
}
}