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old solver: improve normalization of Pointee::Metadata

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This commit is contained in:
Lukas Markeffsky 2024-02-05 14:54:24 +01:00
parent 77fb540684
commit 0c1f401d98
5 changed files with 113 additions and 39 deletions
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37
compiler/rustc_trait_selection/src/traits/project.rs
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@ -1916,10 +1916,11 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
// Integers and floats are always Sized, and so have unit type metadata.
| ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
// type parameters, opaques, and unnormalized projections have pointer
// metadata if they're known (e.g. by the param_env) to be sized
// We normalize from `Wrapper<Tail>::Metadata` to `Tail::Metadata` if able.
// Otherwise, type parameters, opaques, and unnormalized projections have
// unit metadata if they're known (e.g. by the param_env) to be sized.
ty::Param(_) | ty::Alias(..)
if selcx.infcx.predicate_must_hold_modulo_regions(
if self_ty != tail || selcx.infcx.predicate_must_hold_modulo_regions(
&obligation.with(
selcx.tcx(),
ty::TraitRef::from_lang_item(selcx.tcx(), LangItem::Sized, obligation.cause.span(),[self_ty]),
@ -2289,7 +2290,7 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
assert_eq!(metadata_def_id, item_def_id);
let mut obligations = Vec::new();
let (metadata_ty, check_is_sized) = self_ty.ptr_metadata_ty(tcx, |ty| {
let normalize = |ty| {
normalize_with_depth_to(
selcx,
obligation.param_env,
@ -2298,16 +2299,26 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
ty,
&mut obligations,
)
};
let metadata_ty = self_ty.ptr_metadata_ty_or_tail(tcx, normalize).unwrap_or_else(|tail| {
if tail == self_ty {
// This is the fallback case for type parameters, unnormalizable projections
// and opaque types.
// If the `self_ty` is `Sized`, then the metadata is `()`.
let sized_predicate = ty::TraitRef::from_lang_item(
tcx,
LangItem::Sized,
obligation.cause.span(),
[self_ty],
);
obligations.push(obligation.with(tcx, sized_predicate));
tcx.types.unit
} else {
// We know that `self_ty` has the same metadata as `tail`. This allows us
// to prove predicates like `Wrapper<Tail>::Metadata == Tail::Metadata`.
Ty::new_projection(tcx, metadata_def_id, [tail])
}
});
if check_is_sized {
let sized_predicate = ty::TraitRef::from_lang_item(
tcx,
LangItem::Sized,
obligation.cause.span(),
[self_ty],
);
obligations.push(obligation.with(tcx, sized_predicate));
}
(metadata_ty.into(), obligations)
} else {
bug!("unexpected builtin trait with associated type: {:?}", obligation.predicate);