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Rollup merge of #93977 - compiler-errors:sized-generic-metadata, r=wesleywiser

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Type params and assoc types have unit metadata if they are sized

Extend the logic in `Pointee` projection to ensure that we can satisfy `<T as Pointee>::Metadata = ()` if `T: Sized`.

cc: `@SimonSapin` and #93959
This commit is contained in:
Matthias Krüger 2022-03-14 17:24:57 +01:00 • committed by GitHub
commit 774655da5f
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5 changed files with 134 additions and 15 deletions
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23
compiler/rustc_middle/src/ty/sty.rs
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@ -2252,12 +2252,13 @@ impl<'tcx> Ty<'tcx> {
}
}
/// Returns the type of metadata for (potentially fat) pointers to this type.
/// Returns the type of metadata for (potentially fat) pointers to this type,
/// and a boolean signifying if this is conditional on this type being `Sized`.
pub fn ptr_metadata_ty(
self,
tcx: TyCtxt<'tcx>,
normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
) -> Ty<'tcx> {
) -> (Ty<'tcx>, bool) {
let tail = tcx.struct_tail_with_normalize(self, normalize);
match tail.kind() {
// Sized types
@ -2277,28 +2278,30 @@ impl<'tcx> Ty<'tcx> {
| ty::Closure(..)
| ty::Never
| ty::Error(_)
// Extern types have metadata = ().
| 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(..)
// If returned by `struct_tail_without_normalization` this is the empty tuple,
// a.k.a. unit type, which is Sized
| ty::Tuple(..) => tcx.types.unit,
| ty::Tuple(..) => (tcx.types.unit, false),
ty::Str | ty::Slice(_) => tcx.types.usize,
ty::Str | ty::Slice(_) => (tcx.types.usize, false),
ty::Dynamic(..) => {
let dyn_metadata = tcx.lang_items().dyn_metadata().unwrap();
tcx.type_of(dyn_metadata).subst(tcx, &[tail.into()])
(tcx.type_of(dyn_metadata).subst(tcx, &[tail.into()]), false)
},
ty::Projection(_)
| ty::Param(_)
| ty::Opaque(..)
| ty::Infer(ty::TyVar(_))
// type parameters only have unit metadata if they're sized, so return true
// to make sure we double check this during confirmation
ty::Param(_) | ty::Projection(_) | ty::Opaque(..) => (tcx.types.unit, true),
ty::Infer(ty::TyVar(_))
| ty::Bound(..)
| ty::Placeholder(..)
| ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
bug!("`ptr_metadata_ty` applied to unexpected type: {:?}", tail)
bug!("`ptr_metadata_ty` applied to unexpected type: {:?} (tail = {:?})", self, tail)
}
}
}