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Use the normalizing param-env always in check_type_bounds

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This commit is contained in:
Michael Goulet 2023-10-24 15:49:44 +00:00
parent b20f40dba9
commit bb74d7e97d
6 changed files with 176 additions and 152 deletions
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284
compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
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@ -2162,45 +2162,140 @@ 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);
debug!(?param_env);
let container_id = impl_ty.container_id(tcx);
let impl_ty_def_id = impl_ty.def_id.expect_local();
let impl_ty_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id);
let rebased_args = impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args);
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
// A synthetic impl Trait for RPITIT desugaring has no HIR, which we currently use to get the
// span for an impl's associated type. Instead, for these, use the def_span for the synthesized
// associated type.
let impl_ty_span = if impl_ty.is_impl_trait_in_trait() {
tcx.def_span(impl_ty_def_id)
} else {
match tcx.hir().get_by_def_id(impl_ty_def_id) {
hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Type(_, Some(ty)),
..
}) => ty.span,
hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Type(ty), .. }) => ty.span,
_ => bug!(),
}
};
let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl_ty_def_id)?;
let normalize_cause = ObligationCause::new(
impl_ty_span,
impl_ty_def_id,
ObligationCauseCode::CheckAssociatedTypeBounds {
impl_item_def_id: impl_ty.def_id.expect_local(),
trait_item_def_id: trait_ty.def_id,
},
);
let mk_cause = |span: Span| {
let code = if span.is_dummy() {
traits::ItemObligation(trait_ty.def_id)
} else {
traits::BindingObligation(trait_ty.def_id, span)
};
ObligationCause::new(impl_ty_span, impl_ty_def_id, code)
};
let obligations: Vec<_> = tcx
.explicit_item_bounds(trait_ty.def_id)
.iter_instantiated_copied(tcx, rebased_args)
.map(|(concrete_ty_bound, span)| {
debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
traits::Obligation::new(tcx, mk_cause(span), param_env, concrete_ty_bound)
})
.collect();
debug!("check_type_bounds: item_bounds={:?}", obligations);
for mut obligation in util::elaborate(tcx, obligations) {
let normalized_predicate = ocx.normalize(&normalize_cause, param_env, obligation.predicate);
debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
obligation.predicate = normalized_predicate;
ocx.register_obligation(obligation);
}
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
return Err(reported);
}
// Finally, resolve all regions. This catches wily misuses of
// lifetime parameters.
let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_def_id, assumed_wf_types);
let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env)
}
/// Install projection predicates that allow GATs to project to their own
/// definition types. This is not allowed in general in cases of default
/// associated types in trait definitions, or when specialization is involved,
/// but is needed when checking these definition types actually satisfy the
/// trait bounds of the GAT.
///
/// # How it works
///
/// ```ignore (example)
/// impl<A, B> Foo<u32> for (A, B) {
/// type Bar<C> = Wrapper<A, B, C>
/// }
/// ```
///
/// - `impl_trait_ref` would be `<(A, B) as Foo<u32>>`
/// - `normalize_impl_ty_args` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
/// - `normalize_impl_ty` would be `Wrapper<A, B, ^0.0>`
/// - `rebased_args` would be `[(A, B), u32, ^0.0]`, combining the args from
/// the *trait* with the generic associated type parameters (as bound vars).
///
/// A note regarding the use of bound vars here:
/// Imagine as an example
/// ```
/// trait Family {
/// type Member<C: Eq>;
/// }
///
/// impl Family for VecFamily {
/// type Member<C: Eq> = i32;
/// }
/// ```
/// Here, we would generate
/// ```ignore (pseudo-rust)
/// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
/// ```
///
/// when we really would like to generate
/// ```ignore (pseudo-rust)
/// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
/// ```
///
/// But, this is probably fine, because although the first clause can be used with types `C` that
/// do not implement `Eq`, for it to cause some kind of problem, there would have to be a
/// `VecFamily::Member<X>` for some type `X` where `!(X: Eq)`, that appears in the value of type
/// `Member<C: Eq> = ....` That type would fail a well-formedness check that we ought to be doing
/// elsewhere, which would check that any `<T as Family>::Member<X>` meets the bounds declared in
/// 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);
// Given
//
// impl<A, B> Foo<u32> for (A, B) {
// type Bar<C> = Wrapper<A, B, C>
// }
//
// - `impl_trait_ref` would be `<(A, B) as Foo<u32>>`
// - `normalize_impl_ty_args` would be `[A, B, ^0.0]` (`^0.0` here is the bound var with db 0 and index 0)
// - `normalize_impl_ty` would be `Wrapper<A, B, ^0.0>`
// - `rebased_args` would be `[(A, B), u32, ^0.0]`, combining the args from
// the *trait* with the generic associated type parameters (as bound vars).
//
// A note regarding the use of bound vars here:
// Imagine as an example
// ```
// trait Family {
// type Member<C: Eq>;
// }
//
// impl Family for VecFamily {
// type Member<C: Eq> = i32;
// }
// ```
// Here, we would generate
// ```notrust
// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) }
// ```
// when we really would like to generate
// ```notrust
// forall<C> { Normalize(<VecFamily as Family>::Member<C> => i32) :- Implemented(C: Eq) }
// ```
// But, this is probably fine, because although the first clause can be used with types C that
// do not implement Eq, for it to cause some kind of problem, there would have to be a
// VecFamily::Member<X> for some type X where !(X: Eq), that appears in the value of type
// Member<C: Eq> = .... That type would fail a well-formedness check that we ought to be doing
// elsewhere, which would check that any <T as Family>::Member<X> meets the bounds declared in
// the trait (notably, that X: Eq and T: Family).
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
@ -2257,105 +2352,30 @@ pub(super) fn check_type_bounds<'tcx>(
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);
let normalize_param_env = {
let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
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),
),
};
ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing)
};
debug!(?normalize_param_env);
let impl_ty_def_id = impl_ty.def_id.expect_local();
let impl_ty_args = GenericArgs::identity_for_item(tcx, impl_ty.def_id);
let rebased_args = impl_ty_args.rebase_onto(tcx, container_id, impl_trait_ref.args);
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new(&infcx);
// A synthetic impl Trait for RPITIT desugaring has no HIR, which we currently use to get the
// span for an impl's associated type. Instead, for these, use the def_span for the synthesized
// associated type.
let impl_ty_span = if impl_ty.is_impl_trait_in_trait() {
tcx.def_span(impl_ty_def_id)
} else {
match tcx.hir().get_by_def_id(impl_ty_def_id) {
hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Type(_, Some(ty)),
..
}) => ty.span,
hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Type(ty), .. }) => ty.span,
_ => bug!(),
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; }
}
};
let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl_ty_def_id)?;
let normalize_cause = ObligationCause::new(
impl_ty_span,
impl_ty_def_id,
ObligationCauseCode::CheckAssociatedTypeBounds {
impl_item_def_id: impl_ty.def_id.expect_local(),
trait_item_def_id: trait_ty.def_id,
},
);
let mk_cause = |span: Span| {
let code = if span.is_dummy() {
traits::ItemObligation(trait_ty.def_id)
} else {
traits::BindingObligation(trait_ty.def_id, span)
};
ObligationCause::new(impl_ty_span, impl_ty_def_id, code)
_ => 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),
),
};
let obligations: Vec<_> = tcx
.explicit_item_bounds(trait_ty.def_id)
.iter_instantiated_copied(tcx, rebased_args)
.map(|(concrete_ty_bound, span)| {
debug!("check_type_bounds: concrete_ty_bound = {:?}", concrete_ty_bound);
traits::Obligation::new(tcx, mk_cause(span), param_env, concrete_ty_bound)
})
.collect();
debug!("check_type_bounds: item_bounds={:?}", obligations);
for mut obligation in util::elaborate(tcx, obligations) {
let normalized_predicate =
ocx.normalize(&normalize_cause, normalize_param_env, obligation.predicate);
debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
obligation.predicate = normalized_predicate;
ocx.register_obligation(obligation);
}
// Check that all obligations are satisfied by the implementation's
// version.
let errors = ocx.select_all_or_error();
if !errors.is_empty() {
let reported = infcx.err_ctxt().report_fulfillment_errors(errors);
return Err(reported);
}
// Finally, resolve all regions. This catches wily misuses of
// lifetime parameters.
let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_def_id, assumed_wf_types);
let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env)
ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing)
}
fn assoc_item_kind_str(impl_item: &ty::AssocItem) -> &'static str {