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

2 files changed, 5 insertions, 4 deletions

diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 380931742e3..73f86f74d14 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -320,7 +320,7 @@ fn layout_of_uncached<'tcx>(
             }
 
             // Type of the first ADT field:
-            let f0_ty = def.non_enum_variant().fields[0].ty(tcx, substs);
+            let f0_ty = def.non_enum_variant().fields[FieldIdx::from_u32(0)].ty(tcx, substs);
 
             // Heterogeneous SIMD vectors are not supported:
             // (should be caught by typeck)
@@ -456,7 +456,8 @@ fn layout_of_uncached<'tcx>(
                     {
                         let param_env = tcx.param_env(def.did());
                         def.is_struct()
-                            && match def.variants().iter().next().and_then(|x| x.fields.last()) {
+                            && match def.variants().iter().next().and_then(|x| x.fields.raw.last())
+                            {
                                 Some(last_field) => tcx
                                     .type_of(last_field.did)
                                     .subst_identity()
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 50aeb7f440f..cb06c7acff0 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -107,7 +107,7 @@ fn adt_sized_constraint(tcx: TyCtxt<'_>, def_id: DefId) -> &[Ty<'_>] {
     let result = tcx.mk_type_list_from_iter(
         def.variants()
             .iter()
-            .flat_map(|v| v.fields.last())
+            .filter_map(|v| v.fields.raw.last())
             .flat_map(|f| sized_constraint_for_ty(tcx, def, tcx.type_of(f.did).subst_identity())),
     );
 
@@ -542,7 +542,7 @@ fn unsizing_params_for_adt<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> BitSet<u32
 
     // The last field of the structure has to exist and contain type/const parameters.
     let Some((tail_field, prefix_fields)) =
-        def.non_enum_variant().fields.split_last() else
+        def.non_enum_variant().fields.raw.split_last() else
     {
         return BitSet::new_empty(num_params);
     };