Various minor Idx-related tweaks

Nothing particularly exciting here, but a couple of things I noticed as I was looking for more index conversions to simplify.

compiler/rustc_abi/src/layout.rs

@@ -461,8 +461,8 @@ pub trait LayoutCalculator {
             let all_indices = variants.indices();
             let needs_disc =
                 |index: VariantIdx| index != largest_variant_index && !absent(&variants[index]);
-            let niche_variants = all_indices.clone().find(|v| needs_disc(*v)).unwrap().index()
-                ..=all_indices.rev().find(|v| needs_disc(*v)).unwrap().index();
+            let niche_variants = all_indices.clone().find(|v| needs_disc(*v)).unwrap()
+                ..=all_indices.rev().find(|v| needs_disc(*v)).unwrap();
 
             let count = niche_variants.size_hint().1.unwrap() as u128;
 
@@ -560,8 +560,7 @@ pub trait LayoutCalculator {
                     tag: niche_scalar,
                     tag_encoding: TagEncoding::Niche {
                         untagged_variant: largest_variant_index,
-                        niche_variants: (VariantIdx::new(*niche_variants.start())
-                            ..=VariantIdx::new(*niche_variants.end())),
+                        niche_variants,
                         niche_start,
                     },
                     tag_field: 0,

compiler/rustc_abi/src/lib.rs

@@ -11,7 +11,7 @@ use bitflags::bitflags;
 use rustc_data_structures::intern::Interned;
 #[cfg(feature = "nightly")]
 use rustc_data_structures::stable_hasher::StableOrd;
-use rustc_index::vec::{Idx, IndexSlice, IndexVec};
+use rustc_index::vec::{IndexSlice, IndexVec};
 #[cfg(feature = "nightly")]
 use rustc_macros::HashStable_Generic;
 #[cfg(feature = "nightly")]

compiler/rustc_ast/src/node_id.rs

@@ -9,14 +9,14 @@ rustc_index::newtype_index! {
     ///
     /// [`DefId`]: rustc_span::def_id::DefId
     #[debug_format = "NodeId({})"]
-    pub struct NodeId {}
+    pub struct NodeId {
+        /// The [`NodeId`] used to represent the root of the crate.
+        const CRATE_NODE_ID = 0;
+    }
 }
 
 rustc_data_structures::define_id_collections!(NodeMap, NodeSet, NodeMapEntry, NodeId);
 
-/// The [`NodeId`] used to represent the root of the crate.
-pub const CRATE_NODE_ID: NodeId = NodeId::from_u32(0);
-
 /// When parsing and at the beginning of doing expansions, we initially give all AST nodes
 /// this dummy AST [`NodeId`]. Then, during a later phase of expansion, we renumber them
 /// to have small, positive IDs.

compiler/rustc_borrowck/src/diagnostics/var_name.rs

@@ -3,7 +3,7 @@
 
 use crate::region_infer::RegionInferenceContext;
 use crate::Upvar;
-use rustc_index::vec::{Idx, IndexSlice};
+use rustc_index::vec::IndexSlice;
 use rustc_middle::mir::{Body, Local};
 use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_span::source_map::Span;
@@ -117,7 +117,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         argument_index: usize,
     ) -> (Option<Symbol>, Span) {
         let implicit_inputs = self.universal_regions().defining_ty.implicit_inputs();
-        let argument_local = Local::new(implicit_inputs + argument_index + 1);
+        let argument_local = Local::from_usize(implicit_inputs + argument_index + 1);
         debug!("get_argument_name_and_span_for_region: argument_local={argument_local:?}");
 
         let argument_name = local_names[argument_local];

compiler/rustc_borrowck/src/facts.rs

@@ -4,7 +4,6 @@ use crate::location::{LocationIndex, LocationTable};
 use crate::BorrowIndex;
 use polonius_engine::AllFacts as PoloniusFacts;
 use polonius_engine::Atom;
-use rustc_index::vec::Idx;
 use rustc_middle::mir::Local;
 use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_mir_dataflow::move_paths::MovePathIndex;
@@ -93,13 +92,13 @@ impl AllFactsExt for AllFacts {
 
 impl Atom for BorrowIndex {
     fn index(self) -> usize {
-        Idx::index(self)
+        self.as_usize()
     }
 }
 
 impl Atom for LocationIndex {
     fn index(self) -> usize {
-        Idx::index(self)
+        self.as_usize()
     }
 }
 

compiler/rustc_borrowck/src/location.rs

@@ -1,6 +1,6 @@
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::vec::IndexVec;
 use rustc_middle::mir::{BasicBlock, Body, Location};
 
 /// Maps between a MIR Location, which identifies a particular
@@ -50,19 +50,19 @@ impl LocationTable {
     }
 
     pub fn all_points(&self) -> impl Iterator<Item = LocationIndex> {
-        (0..self.num_points).map(LocationIndex::new)
+        (0..self.num_points).map(LocationIndex::from_usize)
     }
 
     pub fn start_index(&self, location: Location) -> LocationIndex {
         let Location { block, statement_index } = location;
         let start_index = self.statements_before_block[block];
-        LocationIndex::new(start_index + statement_index * 2)
+        LocationIndex::from_usize(start_index + statement_index * 2)
     }
 
     pub fn mid_index(&self, location: Location) -> LocationIndex {
         let Location { block, statement_index } = location;
         let start_index = self.statements_before_block[block];
-        LocationIndex::new(start_index + statement_index * 2 + 1)
+        LocationIndex::from_usize(start_index + statement_index * 2 + 1)
     }
 
     pub fn to_location(&self, index: LocationIndex) -> RichLocation {

compiler/rustc_borrowck/src/nll.rs

@@ -7,8 +7,8 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_index::vec::IndexSlice;
 use rustc_middle::mir::{create_dump_file, dump_enabled, dump_mir, PassWhere};
 use rustc_middle::mir::{
-    BasicBlock, Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location,
-    Promoted,
+    Body, ClosureOutlivesSubject, ClosureRegionRequirements, LocalKind, Location, Promoted,
+    START_BLOCK,
 };
 use rustc_middle::ty::{self, OpaqueHiddenType, TyCtxt};
 use rustc_span::symbol::sym;
@@ -94,8 +94,8 @@ fn populate_polonius_move_facts(
         }
     }
 
-    let fn_entry_start = location_table
-        .start_index(Location { block: BasicBlock::from_u32(0u32), statement_index: 0 });
+    let fn_entry_start =
+        location_table.start_index(Location { block: START_BLOCK, statement_index: 0 });
 
     // initialized_at
     for init in move_data.inits.iter() {

compiler/rustc_borrowck/src/type_check/input_output.rs

@@ -7,7 +7,6 @@
 //! `RETURN_PLACE` the MIR arguments) are always fully normalized (and
 //! contain revealed `impl Trait` values).
 
-use rustc_index::vec::Idx;
 use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty};
@@ -83,7 +82,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             }
 
             // In MIR, argument N is stored in local N+1.
-            let local = Local::new(argument_index + 1);
+            let local = Local::from_usize(argument_index + 1);
 
             let mir_input_ty = body.local_decls[local].ty;
 

compiler/rustc_borrowck/src/universal_regions.rs

@@ -19,7 +19,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::BodyOwnerKind;
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::vec::IndexVec;
 use rustc_infer::infer::NllRegionVariableOrigin;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::{self, InlineConstSubsts, InlineConstSubstsParts, RegionVid, Ty, TyCtxt};
@@ -289,7 +289,7 @@ impl<'tcx> UniversalRegions<'tcx> {
     /// Returns an iterator over all the RegionVids corresponding to
     /// universally quantified free regions.
     pub fn universal_regions(&self) -> impl Iterator<Item = RegionVid> {
-        (FIRST_GLOBAL_INDEX..self.num_universals).map(RegionVid::new)
+        (FIRST_GLOBAL_INDEX..self.num_universals).map(RegionVid::from_usize)
     }
 
     /// Returns `true` if `r` is classified as an local region.

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -12,7 +12,6 @@ use crate::MemFlags;
 use rustc_ast as ast;
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_hir::lang_items::LangItem;
-use rustc_index::vec::Idx;
 use rustc_middle::mir::{self, AssertKind, SwitchTargets};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, ValidityRequirement};
 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
@@ -369,7 +368,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         if self.fn_abi.c_variadic {
             // The `VaList` "spoofed" argument is just after all the real arguments.
             let va_list_arg_idx = self.fn_abi.args.len();
-            match self.locals[mir::Local::new(1 + va_list_arg_idx)] {
+            match self.locals[mir::Local::from_usize(1 + va_list_arg_idx)] {
                 LocalRef::Place(va_list) => {
                     bx.va_end(va_list.llval);
                 }

compiler/rustc_const_eval/src/interpret/discriminant.rs

@@ -211,18 +211,19 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                             let variant_index_relative = u32::try_from(variant_index_relative)
                                 .expect("we checked that this fits into a u32");
                             // Then computing the absolute variant idx should not overflow any more.
-                            let variant_index = variants_start
-                                .checked_add(variant_index_relative)
-                                .expect("overflow computing absolute variant idx");
-                            let variants_len = op
+                            let variant_index = VariantIdx::from_u32(
+                                variants_start
+                                    .checked_add(variant_index_relative)
+                                    .expect("overflow computing absolute variant idx"),
+                            );
+                            let variants = op
                                 .layout
                                 .ty
                                 .ty_adt_def()
                                 .expect("tagged layout for non adt")
-                                .variants()
-                                .len();
-                            assert!(usize::try_from(variant_index).unwrap() < variants_len);
-                            VariantIdx::from_u32(variant_index)
+                                .variants();
+                            assert!(variant_index < variants.next_index());
+                            variant_index
                         } else {
                             untagged_variant
                         }

compiler/rustc_hir_typeck/src/demand.rs

@@ -17,7 +17,6 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Article, AssocItem, Ty, TypeAndMut, TypeFoldable};
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{BytePos, Span, DUMMY_SP};
-use rustc_target::abi::FieldIdx;
 use rustc_trait_selection::infer::InferCtxtExt as _;
 use rustc_trait_selection::traits::ObligationCause;
 
@@ -875,7 +874,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     variant.fields.len() == 1
                 })
                 .filter_map(|variant| {
-                    let sole_field = &variant.fields[FieldIdx::from_u32(0)];
+                    let sole_field = &variant.single_field();
 
                     let field_is_local = sole_field.did.is_local();
                     let field_is_accessible =

compiler/rustc_hir_typeck/src/intrinsicck.rs

@@ -4,7 +4,7 @@ use rustc_hir as hir;
 use rustc_index::vec::Idx;
 use rustc_middle::ty::layout::{LayoutError, SizeSkeleton};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
-use rustc_target::abi::{FieldIdx, Pointer, VariantIdx};
+use rustc_target::abi::{Pointer, VariantIdx};
 
 use super::FnCtxt;
 
@@ -28,7 +28,7 @@ fn unpack_option_like<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
         }
 
         if def.variant(data_idx).fields.len() == 1 {
-            return def.variant(data_idx).fields[FieldIdx::from_u32(0)].ty(tcx, substs);
+            return def.variant(data_idx).single_field().ty(tcx, substs);
         }
     }
 

compiler/rustc_infer/src/infer/error_reporting/suggest.rs

@@ -10,7 +10,6 @@ use rustc_middle::traits::{
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self as ty, GenericArgKind, IsSuggestable, Ty, TypeVisitableExt};
 use rustc_span::{sym, BytePos, Span};
-use rustc_target::abi::FieldIdx;
 
 use crate::errors::{
     ConsiderAddingAwait, FnConsiderCasting, FnItemsAreDistinct, FnUniqTypes,
@@ -114,7 +113,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         variant.fields.len() == 1 && variant.ctor_kind() == Some(CtorKind::Fn)
                     })
                     .filter_map(|variant| {
-                        let sole_field = &variant.fields[FieldIdx::from_u32(0)];
+                        let sole_field = &variant.single_field();
                         let sole_field_ty = sole_field.ty(self.tcx, substs);
                         if self.same_type_modulo_infer(sole_field_ty, exp_found.found) {
                             let variant_path =

compiler/rustc_middle/src/ty/mod.rs

@@ -1969,6 +1969,16 @@ impl VariantDef {
     pub fn ctor_def_id(&self) -> Option<DefId> {
         self.ctor.map(|(_, def_id)| def_id)
     }
+
+    /// Returns the one field in this variant.
+    ///
+    /// `panic!`s if there are no fields or multiple fields.
+    #[inline]
+    pub fn single_field(&self) -> &FieldDef {
+        assert!(self.fields.len() == 1);
+
+        &self.fields[FieldIdx::from_u32(0)]
+    }
 }
 
 impl PartialEq for VariantDef {

compiler/rustc_query_system/src/dep_graph/query.rs

@@ -24,10 +24,7 @@ impl<K: DepKind> DepGraphQuery<K> {
 
     pub fn push(&mut self, index: DepNodeIndex, node: DepNode<K>, edges: &[DepNodeIndex]) {
         let source = self.graph.add_node(node);
-        if index.index() >= self.dep_index_to_index.len() {
-            self.dep_index_to_index.resize(index.index() + 1, None);
-        }
-        self.dep_index_to_index[index] = Some(source);
+        self.dep_index_to_index.insert(index, source);
         self.indices.insert(node, source);
 
         for &target in edges.iter() {

compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs

@@ -11,12 +11,13 @@
 use super::{CanonicalGoal, Certainty, EvalCtxt, Goal};
 use crate::solve::canonicalize::{CanonicalizeMode, Canonicalizer};
 use crate::solve::{CanonicalResponse, QueryResult, Response};
+use rustc_index::vec::IndexVec;
 use rustc_infer::infer::canonical::query_response::make_query_region_constraints;
 use rustc_infer::infer::canonical::CanonicalVarValues;
 use rustc_infer::infer::canonical::{CanonicalExt, QueryRegionConstraints};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::solve::{ExternalConstraints, ExternalConstraintsData};
-use rustc_middle::ty::{self, GenericArgKind};
+use rustc_middle::ty::{self, BoundVar, GenericArgKind};
 use rustc_span::DUMMY_SP;
 use std::iter;
 use std::ops::Deref;
@@ -139,25 +140,25 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         //
         // We therefore instantiate the existential variable in the canonical response with the
         // inference variable of the input right away, which is more performant.
-        let mut opt_values = vec![None; response.variables.len()];
+        let mut opt_values = IndexVec::from_elem_n(None, response.variables.len());
         for (original_value, result_value) in iter::zip(original_values, var_values.var_values) {
             match result_value.unpack() {
                 GenericArgKind::Type(t) => {
                     if let &ty::Bound(debruijn, b) = t.kind() {
                         assert_eq!(debruijn, ty::INNERMOST);
-                        opt_values[b.var.index()] = Some(*original_value);
+                        opt_values[b.var] = Some(*original_value);
                     }
                 }
                 GenericArgKind::Lifetime(r) => {
                     if let ty::ReLateBound(debruijn, br) = *r {
                         assert_eq!(debruijn, ty::INNERMOST);
-                        opt_values[br.var.index()] = Some(*original_value);
+                        opt_values[br.var] = Some(*original_value);
                     }
                 }
                 GenericArgKind::Const(c) => {
                     if let ty::ConstKind::Bound(debrujin, b) = c.kind() {
                         assert_eq!(debrujin, ty::INNERMOST);
-                        opt_values[b.index()] = Some(*original_value);
+                        opt_values[b] = Some(*original_value);
                     }
                 }
             }
@@ -180,7 +181,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
                     // more placeholders then they should be able to. However the inference variables have
                     // to "come from somewhere", so by equating them with the original values of the caller
                     // later on, we pull them down into their correct universe again.
-                    if let Some(v) = opt_values[index] {
+                    if let Some(v) = opt_values[BoundVar::from_usize(index)] {
                         v
                     } else {
                         self.infcx.instantiate_canonical_var(DUMMY_SP, info, |_| prev_universe)