eb3e9c1f45
Update `ty::VariantDef` to use `IndexVec<FieldIdx, FieldDef>` And while doing the updates for that, also uses `FieldIdx` in `ProjectionKind::Field` and `TypeckResults::field_indices`. There's more places that could use it (like `rustc_const_eval` and `LayoutS`), but I tried to keep this PR from exploding to *even more* places. Part 2/? of https://github.com/rust-lang/compiler-team/issues/606
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.