bjoernager/rust
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type parameters have unit metadata if they are sized

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This commit is contained in:
Michael Goulet 2022-02-13 13:39:07 -08:00
parent 6d7684101a
commit ef0ba1d2ce
3 changed files with 47 additions and 14 deletions
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27
compiler/rustc_trait_selection/src/traits/project.rs
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@ -1399,6 +1399,8 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
let tail = selcx.tcx().struct_tail_with_normalize(self_ty, |ty| {
// We throw away any obligations we get from this, since we normalize
// and confirm these obligations once again during confirmation
normalize_with_depth(
selcx,
obligation.param_env,
@ -1415,7 +1417,6 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Foreign(_)
| ty::Str
| ty::Array(..)
| ty::Slice(_)
@ -1428,6 +1429,8 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
| ty::Generator(..)
| ty::GeneratorWitness(..)
| ty::Never
// Extern types have unit metadata, according to RFC 2850
| ty::Foreign(_)
// If returned by `struct_tail_without_normalization` this is a unit struct
// without any fields, or not a struct, and therefore is Sized.
| ty::Adt(..)
@ -1436,9 +1439,10 @@ 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,
ty::Projection(..)
| ty::Opaque(..)
| ty::Param(..)
// type parameters and unnormalized projections have pointer metadata if they're still known to be sized
ty::Param(_) | ty::Projection(..) => tail.is_sized(selcx.tcx().at(obligation.cause.span), obligation.param_env),
ty::Opaque(..)
| ty::Bound(..)
| ty::Placeholder(..)
| ty::Infer(..)
@ -1657,7 +1661,7 @@ fn confirm_pointee_candidate<'cx, 'tcx>(
let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
let mut obligations = vec![];
let metadata_ty = self_ty.ptr_metadata_ty(tcx, |ty| {
let (metadata_ty, check_is_sized) = self_ty.ptr_metadata_ty(tcx, |ty| {
normalize_with_depth_to(
selcx,
obligation.param_env,
@ -1667,6 +1671,19 @@ fn confirm_pointee_candidate<'cx, 'tcx>(
&mut obligations,
)
});
if check_is_sized {
let sized_predicate = ty::Binder::dummy(ty::TraitRef::new(
tcx.require_lang_item(LangItem::Sized, None),
tcx.mk_substs_trait(self_ty, &[]),
))
.without_const()
.to_predicate(tcx);
obligations.push(Obligation::new(
obligation.cause.clone(),
obligation.param_env,
sized_predicate,
));
}
let substs = tcx.mk_substs([self_ty.into()].iter());
let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);