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Add all RPITITs when augmenting param-env with GAT bounds in check_ty…
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…pe_bounds
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@compiler-errors
compiler-errors committed Oct 25, 2023
1 parent 69563f0 commit bfd836b
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Showing 2 changed files with 114 additions and 77 deletions.
180 changes: 103 additions & 77 deletions compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2162,7 +2162,7 @@ pub(super) fn check_type_bounds<'tcx>(
impl_ty: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> Result<(), ErrorGuaranteed> {
let param_env = param_env_with_gat_bounds(tcx, trait_ty, impl_ty, impl_trait_ref);
let param_env = param_env_with_gat_bounds(tcx, impl_ty, impl_trait_ref);
debug!(?param_env);

let container_id = impl_ty.container_id(tcx);
Expand Down Expand Up @@ -2288,92 +2288,118 @@ pub(super) fn check_type_bounds<'tcx>(
/// the trait (notably, that `X: Eq` and `T: Family`).
fn param_env_with_gat_bounds<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ty: ty::AssocItem,
impl_ty: ty::AssocItem,
impl_trait_ref: ty::TraitRef<'tcx>,
) -> ty::ParamEnv<'tcx> {
let param_env = tcx.param_env(impl_ty.def_id);
let container_id = impl_ty.container_id(tcx);
let mut predicates = param_env.caller_bounds().to_vec();

let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
smallvec::SmallVec::with_capacity(tcx.generics_of(impl_ty.def_id).params.len());
// Extend the impl's identity args with late-bound GAT vars
let normalize_impl_ty_args = ty::GenericArgs::identity_for_item(tcx, container_id).extend_to(
tcx,
impl_ty.def_id,
|param, _| match param.kind {
GenericParamDefKind::Type { .. } => {
let kind = ty::BoundTyKind::Param(param.def_id, param.name);
let bound_var = ty::BoundVariableKind::Ty(kind);
bound_vars.push(bound_var);
Ty::new_bound(
tcx,
ty::INNERMOST,
ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
)
.into()
// for RPITITs, we should install predicates that allow us to project all
// of the RPITITs associated with the same body. This is because checking
// the item bounds of RPITITs often involves nested RPITITs having to prove
// bounds about themselves.
let impl_tys_to_install = match impl_ty.opt_rpitit_info {
None => vec![impl_ty],
Some(
ty::ImplTraitInTraitData::Impl { fn_def_id }
| ty::ImplTraitInTraitData::Trait { fn_def_id, .. },
) => tcx
.associated_types_for_impl_traits_in_associated_fn(fn_def_id)
.iter()
.map(|def_id| tcx.associated_item(*def_id))
.collect(),
};

for impl_ty in impl_tys_to_install {
let trait_ty = match impl_ty.container {
ty::AssocItemContainer::TraitContainer => impl_ty,
ty::AssocItemContainer::ImplContainer => {
tcx.associated_item(impl_ty.trait_item_def_id.unwrap())
}
GenericParamDefKind::Lifetime => {
let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
let bound_var = ty::BoundVariableKind::Region(kind);
bound_vars.push(bound_var);
ty::Region::new_late_bound(
tcx,
ty::INNERMOST,
ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
)
.into()
};

let mut bound_vars: smallvec::SmallVec<[ty::BoundVariableKind; 8]> =
smallvec::SmallVec::with_capacity(tcx.generics_of(impl_ty.def_id).params.len());
// Extend the impl's identity args with late-bound GAT vars
let normalize_impl_ty_args = ty::GenericArgs::identity_for_item(tcx, container_id)
.extend_to(tcx, impl_ty.def_id, |param, _| match param.kind {
GenericParamDefKind::Type { .. } => {
let kind = ty::BoundTyKind::Param(param.def_id, param.name);
let bound_var = ty::BoundVariableKind::Ty(kind);
bound_vars.push(bound_var);
Ty::new_bound(
tcx,
ty::INNERMOST,
ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
)
.into()
}
GenericParamDefKind::Lifetime => {
let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
let bound_var = ty::BoundVariableKind::Region(kind);
bound_vars.push(bound_var);
ty::Region::new_late_bound(
tcx,
ty::INNERMOST,
ty::BoundRegion {
var: ty::BoundVar::from_usize(bound_vars.len() - 1),
kind,
},
)
.into()
}
GenericParamDefKind::Const { .. } => {
let bound_var = ty::BoundVariableKind::Const;
bound_vars.push(bound_var);
ty::Const::new_bound(
tcx,
ty::INNERMOST,
ty::BoundVar::from_usize(bound_vars.len() - 1),
tcx.type_of(param.def_id)
.no_bound_vars()
.expect("const parameter types cannot be generic"),
)
.into()
}
});
// When checking something like
//
// trait X { type Y: PartialEq<<Self as X>::Y> }
// impl X for T { default type Y = S; }
//
// We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
// we want <T as X>::Y to normalize to S. This is valid because we are
// checking the default value specifically here. Add this equality to the
// ParamEnv for normalization specifically.
let normalize_impl_ty =
tcx.type_of(impl_ty.def_id).instantiate(tcx, normalize_impl_ty_args);
let rebased_args =
normalize_impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args);
let bound_vars = tcx.mk_bound_variable_kinds(&bound_vars);

match normalize_impl_ty.kind() {
ty::Alias(ty::Projection, proj)
if proj.def_id == trait_ty.def_id && proj.args == rebased_args =>
{
// Don't include this predicate if the projected type is
// exactly the same as the projection. This can occur in
// (somewhat dubious) code like this:
//
// impl<T> X for T where T: X { type Y = <T as X>::Y; }
}
GenericParamDefKind::Const { .. } => {
let bound_var = ty::BoundVariableKind::Const;
bound_vars.push(bound_var);
ty::Const::new_bound(
tcx,
ty::INNERMOST,
ty::BoundVar::from_usize(bound_vars.len() - 1),
tcx.type_of(param.def_id)
.no_bound_vars()
.expect("const parameter types cannot be generic"),
_ => predicates.push(
ty::Binder::bind_with_vars(
ty::ProjectionPredicate {
projection_ty: ty::AliasTy::new(tcx, trait_ty.def_id, rebased_args),
term: normalize_impl_ty.into(),
},
bound_vars,
)
.into()
}
},
);
// When checking something like
//
// trait X { type Y: PartialEq<<Self as X>::Y> }
// impl X for T { default type Y = S; }
//
// We will have to prove the bound S: PartialEq<<T as X>::Y>. In this case
// we want <T as X>::Y to normalize to S. This is valid because we are
// checking the default value specifically here. Add this equality to the
// ParamEnv for normalization specifically.
let normalize_impl_ty = tcx.type_of(impl_ty.def_id).instantiate(tcx, normalize_impl_ty_args);
let rebased_args = normalize_impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args);
let bound_vars = tcx.mk_bound_variable_kinds(&bound_vars);

match normalize_impl_ty.kind() {
ty::Alias(ty::Projection, proj)
if proj.def_id == trait_ty.def_id && proj.args == rebased_args =>
{
// Don't include this predicate if the projected type is
// exactly the same as the projection. This can occur in
// (somewhat dubious) code like this:
//
// impl<T> X for T where T: X { type Y = <T as X>::Y; }
}
_ => predicates.push(
ty::Binder::bind_with_vars(
ty::ProjectionPredicate {
projection_ty: ty::AliasTy::new(tcx, trait_ty.def_id, rebased_args),
term: normalize_impl_ty.into(),
},
bound_vars,
)
.to_predicate(tcx),
),
};
.to_predicate(tcx),
),
};
}

ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing)
}
Expand Down
11 changes: 11 additions & 0 deletions tests/ui/impl-trait/in-trait/nested-rpitit-bounds.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
// check-pass

use std::ops::Deref;

trait Foo {
fn foo() -> impl Deref<Target = impl Deref<Target = impl Sized>> {
&&()
}
}

fn main() {}

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