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

3 files changed, 10 insertions, 5 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/valtrees.rs b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
index 8e4454d7cec..4d54c01830b 100644
--- a/compiler/rustc_const_eval/src/const_eval/valtrees.rs
+++ b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
@@ -8,7 +8,7 @@ use crate::interpret::{
 use crate::interpret::{MPlaceTy, Value};
 use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
 use rustc_span::source_map::DUMMY_SP;
-use rustc_target::abi::{Align, VariantIdx, FIRST_VARIANT};
+use rustc_target::abi::{Align, FieldIdx, VariantIdx, FIRST_VARIANT};
 
 #[instrument(skip(ecx), level = "debug")]
 fn branches<'tcx>(
@@ -412,6 +412,7 @@ fn valtree_into_mplace<'tcx>(
 
                         let inner_ty = match ty.kind() {
                             ty::Adt(def, substs) => {
+                                let i = FieldIdx::from_usize(i);
                                 def.variant(FIRST_VARIANT).fields[i].ty(tcx, substs)
                             }
                             ty::Tuple(inner_tys) => inner_tys[i],
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index f7881c50960..93b5273e1b1 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -16,7 +16,9 @@ use rustc_middle::mir::interpret::InterpError;
 use rustc_middle::ty;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_span::symbol::{sym, Symbol};
-use rustc_target::abi::{Abi, Scalar as ScalarAbi, Size, VariantIdx, Variants, WrappingRange};
+use rustc_target::abi::{
+    Abi, FieldIdx, Scalar as ScalarAbi, Size, VariantIdx, Variants, WrappingRange,
+};
 
 use std::hash::Hash;
 
@@ -269,14 +271,16 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 match layout.variants {
                     Variants::Single { index } => {
                         // Inside a variant
-                        PathElem::Field(def.variant(index).fields[field].name)
+                        PathElem::Field(def.variant(index).fields[FieldIdx::from_usize(field)].name)
                     }
                     Variants::Multiple { .. } => bug!("we handled variants above"),
                 }
             }
 
             // other ADTs
-            ty::Adt(def, _) => PathElem::Field(def.non_enum_variant().fields[field].name),
+            ty::Adt(def, _) => {
+                PathElem::Field(def.non_enum_variant().fields[FieldIdx::from_usize(field)].name)
+            }
 
             // arrays/slices
             ty::Array(..) | ty::Slice(..) => PathElem::ArrayElem(field),
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 2be385d551e..cd5c92f7342 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -360,7 +360,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     }
                     ty::Adt(adt_def, substs) => {
                         let var = parent_ty.variant_index.unwrap_or(FIRST_VARIANT);
-                        let Some(field) = adt_def.variant(var).fields.get(f.as_usize()) else {
+                        let Some(field) = adt_def.variant(var).fields.get(f) else {
                             fail_out_of_bounds(self, location);
                             return;
                         };