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Rollup merge of #113182 - compiler-errors:rpit-stricter-captures, r=oli-obk

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Error when RPITITs' hidden types capture more lifetimes than their trait definitions

This implements a stricter set of captures rules for RPITITs. They now may only capture:
1. Lifetimes from the impl header (both the self type and any trait substs -- we may want to restrict just to the self type's lifetimes, but the PR makes that easy to do, too)
2. Lifetimes mentioned by the `impl Trait` in the trait method's definition.

Namely, they may not mention lifetimes from the method (early or late) that are not mentioned in the `impl Trait`.

cc #105258 which I think was trying to do this too, though I'm not super familiar with what exactly differs from that or why that one was broken.
cc #112194 (doesn't fix this issue per se, because it's still an open question, but I think this is objectively better than the status quo, and gets us closer to resolving that issue.)

Technically is a fix for the ICE in #108580, but it turns that issue into an error now. We can decide separately whether or not nested RPITITs should capture lifetimes from their parents.

r? ``@oli-obk``
This commit is contained in:
Matthias Krüger 2023-07-01 13:46:01 +02:00 • committed by GitHub
commit ca7e27a71c
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5 changed files with 285 additions and 58 deletions
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148
compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
View file

@ -19,7 +19,7 @@ use rustc_middle::ty::{
self, InternalSubsts, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
};
use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
use rustc_span::Span;
use rustc_span::{Span, DUMMY_SP};
use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
use rustc_trait_selection::traits::{
@ -651,11 +651,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
let impl_sig = ocx.normalize(
&norm_cause,
param_env,
infcx.instantiate_binder_with_fresh_vars(
return_span,
infer::HigherRankedType,
tcx.fn_sig(impl_m.def_id).subst_identity(),
),
tcx.liberate_late_bound_regions(impl_m.def_id, tcx.fn_sig(impl_m.def_id).subst_identity()),
);
impl_sig.error_reported()?;
let impl_return_ty = impl_sig.output();
@ -665,9 +661,10 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
// them with inference variables.
// We will use these inference variables to collect the hidden types of RPITITs.
let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_def_id);
let unnormalized_trait_sig = tcx
.liberate_late_bound_regions(
impl_m.def_id,
let unnormalized_trait_sig = infcx
.instantiate_binder_with_fresh_vars(
return_span,
infer::HigherRankedType,
tcx.fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs),
)
.fold_with(&mut collector);
@ -760,15 +757,17 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
let mut collected_tys = FxHashMap::default();
for (def_id, (ty, substs)) in collected_types {
match infcx.fully_resolve(ty) {
Ok(ty) => {
match infcx.fully_resolve((ty, substs)) {
Ok((ty, substs)) => {
// `ty` contains free regions that we created earlier while liberating the
// trait fn signature. However, projection normalization expects `ty` to
// contains `def_id`'s early-bound regions.
let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
debug!(?id_substs, ?substs);
let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> =
std::iter::zip(substs, id_substs).collect();
let map: FxHashMap<_, _> = std::iter::zip(substs, id_substs)
.skip(tcx.generics_of(trait_m.def_id).count())
.filter_map(|(a, b)| Some((a.as_region()?, b.as_region()?)))
.collect();
debug!(?map);
// NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound
@ -793,25 +792,19 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
// same generics.
let num_trait_substs = trait_to_impl_substs.len();
let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
let ty = tcx.fold_regions(ty, |region, _| {
match region.kind() {
// Remap all free regions, which correspond to late-bound regions in the function.
ty::ReFree(_) => {}
// Remap early-bound regions as long as they don't come from the `impl` itself.
ty::ReEarlyBound(ebr) if tcx.parent(ebr.def_id) != impl_m.container_id(tcx) => {}
_ => return region,
}
let Some(ty::ReEarlyBound(e)) = map.get(&region.into()).map(|r| r.expect_region().kind())
else {
return ty::Region::new_error_with_message(tcx, return_span, "expected ReFree to map to ReEarlyBound")
};
ty::Region::new_early_bound(tcx, ty::EarlyBoundRegion {
def_id: e.def_id,
name: e.name,
index: (e.index as usize - num_trait_substs + num_impl_substs) as u32,
})
});
debug!(%ty);
let ty = match ty.try_fold_with(&mut RemapHiddenTyRegions {
tcx,
map,
num_trait_substs,
num_impl_substs,
def_id,
impl_def_id: impl_m.container_id(tcx),
ty,
return_span,
}) {
Ok(ty) => ty,
Err(guar) => tcx.ty_error(guar),
};
collected_tys.insert(def_id, ty::EarlyBinder::bind(ty));
}
Err(err) => {
@ -895,6 +888,97 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ImplTraitInTraitCollector<'_, 'tcx> {
}
}
struct RemapHiddenTyRegions<'tcx> {
tcx: TyCtxt<'tcx>,
map: FxHashMap<ty::Region<'tcx>, ty::Region<'tcx>>,
num_trait_substs: usize,
num_impl_substs: usize,
def_id: DefId,
impl_def_id: DefId,
ty: Ty<'tcx>,
return_span: Span,
}
impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
type Error = ErrorGuaranteed;
fn interner(&self) -> TyCtxt<'tcx> {
self.tcx
}
fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
if let ty::Alias(ty::Opaque, ty::AliasTy { substs, def_id, .. }) = *t.kind() {
let mut mapped_substs = Vec::with_capacity(substs.len());
for (arg, v) in std::iter::zip(substs, self.tcx.variances_of(def_id)) {
mapped_substs.push(match (arg.unpack(), v) {
// Skip uncaptured opaque substs
(ty::GenericArgKind::Lifetime(_), ty::Bivariant) => arg,
_ => arg.try_fold_with(self)?,
});
}
Ok(self.tcx.mk_opaque(def_id, self.tcx.mk_substs(&mapped_substs)))
} else {
t.try_super_fold_with(self)
}
}
fn try_fold_region(
&mut self,
region: ty::Region<'tcx>,
) -> Result<ty::Region<'tcx>, Self::Error> {
match region.kind() {
// Remap all free regions, which correspond to late-bound regions in the function.
ty::ReFree(_) => {}
// Remap early-bound regions as long as they don't come from the `impl` itself,
// in which case we don't really need to renumber them.
ty::ReEarlyBound(ebr) if self.tcx.parent(ebr.def_id) != self.impl_def_id => {}
_ => return Ok(region),
}
let e = if let Some(region) = self.map.get(&region) {
if let ty::ReEarlyBound(e) = region.kind() { e } else { bug!() }
} else {
let guar = match region.kind() {
ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. })
| ty::ReFree(ty::FreeRegion {
bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
..
}) => {
let return_span = if let ty::Alias(ty::Opaque, opaque_ty) = self.ty.kind() {
self.tcx.def_span(opaque_ty.def_id)
} else {
self.return_span
};
self.tcx
.sess
.struct_span_err(
return_span,
"return type captures more lifetimes than trait definition",
)
.span_label(self.tcx.def_span(def_id), "this lifetime was captured")
.span_note(
self.tcx.def_span(self.def_id),
"hidden type must only reference lifetimes captured by this impl trait",
)
.note(format!("hidden type inferred to be `{}`", self.ty))
.emit()
}
_ => self.tcx.sess.delay_span_bug(DUMMY_SP, "should've been able to remap region"),
};
return Err(guar);
};
Ok(ty::Region::new_early_bound(
self.tcx,
ty::EarlyBoundRegion {
def_id: e.def_id,
name: e.name,
index: (e.index as usize - self.num_trait_substs + self.num_impl_substs) as u32,
},
))
}
}
fn report_trait_method_mismatch<'tcx>(
infcx: &InferCtxt<'tcx>,
mut cause: ObligationCause<'tcx>,