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Rollup merge of #89441 - Nadrieril:fix-89393, r=tmandry

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Normalize after substituting via `field.ty()`

Back in https://github.com/rust-lang/rust/issues/72476 I hadn't understood where the problem was coming from, and only worked around the issue. What happens is that calling `field.ty()` on a field of a generic struct substitutes the appropriate generics but doesn't normalize the resulting type.
As a consumer of types I'm surprised that one would substitute without normalizing, feels like a footgun, so I added a comment.

Fixes https://github.com/rust-lang/rust/issues/89393.
This commit is contained in:
Manish Goregaokar 2021-10-01 14:46:52 -07:00 • committed by GitHub
commit 5ab1245303
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5 changed files with 62 additions and 27 deletions
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4
compiler/rustc_middle/src/ty/mod.rs
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@ -1640,8 +1640,8 @@ impl ReprOptions {
}
impl<'tcx> FieldDef {
/// Returns the type of this field. The `subst` is typically obtained
/// via the second field of `TyKind::AdtDef`.
/// Returns the type of this field. The resulting type is not normalized. The `subst` is
/// typically obtained via the second field of `TyKind::AdtDef`.
pub fn ty(&self, tcx: TyCtxt<'tcx>, subst: SubstsRef<'tcx>) -> Ty<'tcx> {
tcx.type_of(self.did).subst(tcx, subst)
}