Use &IndexSlice instead of &IndexVec where possible

All the same reasons as for `[T]`: more general, less pointer chasing, and `&mut IndexSlice` emphasizes that it doesn't change *length*.

compiler/rustc_abi/src/layout.rs

@@ -289,7 +289,7 @@ pub trait LayoutCalculator {
     fn layout_of_struct_or_enum(
         &self,
         repr: &ReprOptions,
-        variants: &IndexVec<VariantIdx, Vec<Layout<'_>>>,
+        variants: &IndexSlice<VariantIdx, Vec<Layout<'_>>>,
         is_enum: bool,
         is_unsafe_cell: bool,
         scalar_valid_range: (Bound<u128>, Bound<u128>),
@@ -883,7 +883,7 @@ pub trait LayoutCalculator {
     fn layout_of_union(
         &self,
         repr: &ReprOptions,
-        variants: &IndexVec<VariantIdx, Vec<Layout<'_>>>,
+        variants: &IndexSlice<VariantIdx, Vec<Layout<'_>>>,
     ) -> Option<LayoutS> {
         let dl = self.current_data_layout();
         let dl = dl.borrow();

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, IndexVec};
+use rustc_index::vec::{Idx, IndexSlice, IndexVec};
 #[cfg(feature = "nightly")]
 use rustc_macros::HashStable_Generic;
 #[cfg(feature = "nightly")]

compiler/rustc_ast_lowering/src/item.rs

@@ -12,7 +12,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_hir::PredicateOrigin;
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::vec::{Idx, IndexSlice, IndexVec};
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::source_map::DesugaringKind;
@@ -25,7 +25,7 @@ use thin_vec::ThinVec;
 pub(super) struct ItemLowerer<'a, 'hir> {
     pub(super) tcx: TyCtxt<'hir>,
     pub(super) resolver: &'a mut ResolverAstLowering,
-    pub(super) ast_index: &'a IndexVec<LocalDefId, AstOwner<'a>>,
+    pub(super) ast_index: &'a IndexSlice<LocalDefId, AstOwner<'a>>,
     pub(super) owners: &'a mut IndexVec<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
 }
 

compiler/rustc_ast_lowering/src/lib.rs

@@ -60,7 +60,7 @@ use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
 use rustc_hir::definitions::DefPathData;
 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::vec::{Idx, IndexSlice, IndexVec};
 use rustc_macros::fluent_messages;
 use rustc_middle::{
     span_bug,
@@ -414,7 +414,7 @@ fn index_crate<'a>(
 /// This hash will then be part of the crate_hash which is stored in the metadata.
 fn compute_hir_hash(
     tcx: TyCtxt<'_>,
-    owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
+    owners: &IndexSlice<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
 ) -> Fingerprint {
     let mut hir_body_nodes: Vec<_> = owners
         .iter_enumerated()

compiler/rustc_borrowck/src/constraints/mod.rs

@@ -2,7 +2,7 @@
 #![deny(rustc::diagnostic_outside_of_impl)]
 
 use rustc_data_structures::graph::scc::Sccs;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::{RegionVid, VarianceDiagInfo};
 use rustc_span::Span;
@@ -60,7 +60,9 @@ impl<'tcx> OutlivesConstraintSet<'tcx> {
         Sccs::new(region_graph)
     }
 
-    pub(crate) fn outlives(&self) -> &IndexVec<OutlivesConstraintIndex, OutlivesConstraint<'tcx>> {
+    pub(crate) fn outlives(
+        &self,
+    ) -> &IndexSlice<OutlivesConstraintIndex, OutlivesConstraint<'tcx>> {
         &self.outlives
     }
 }

compiler/rustc_borrowck/src/consumers.rs

@@ -3,7 +3,7 @@
 //! This file provides API for compiler consumers.
 
 use rustc_hir::def_id::LocalDefId;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
 use rustc_middle::mir::Body;
 use rustc_middle::ty::{self, TyCtxt};
@@ -35,6 +35,6 @@ pub fn get_body_with_borrowck_facts(
     let (input_body, promoted) = tcx.mir_promoted(def);
     let infcx = tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(def.did)).build();
     let input_body: &Body<'_> = &input_body.borrow();
-    let promoted: &IndexVec<_, _> = &promoted.borrow();
+    let promoted: &IndexSlice<_, _> = &promoted.borrow();
     *super::do_mir_borrowck(&infcx, input_body, promoted, true).1.unwrap()
 }

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -3,7 +3,7 @@
 use rustc_errors::{Applicability, Diagnostic};
 use rustc_hir as hir;
 use rustc_hir::intravisit::Visitor;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_infer::infer::NllRegionVariableOrigin;
 use rustc_middle::mir::{
     Body, CastKind, ConstraintCategory, FakeReadCause, Local, LocalInfo, Location, Operand, Place,
@@ -60,7 +60,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
         &self,
         tcx: TyCtxt<'tcx>,
         body: &Body<'tcx>,
-        local_names: &IndexVec<Local, Option<Symbol>>,
+        local_names: &IndexSlice<Local, Option<Symbol>>,
         err: &mut Diagnostic,
         borrow_desc: &str,
         borrow_span: Option<Span>,

compiler/rustc_borrowck/src/diagnostics/var_name.rs

@@ -3,7 +3,7 @@
 
 use crate::Upvar;
 use crate::{nll::ToRegionVid, region_infer::RegionInferenceContext};
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::vec::{Idx, IndexSlice};
 use rustc_middle::mir::{Body, Local};
 use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_span::source_map::Span;
@@ -14,7 +14,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         &self,
         tcx: TyCtxt<'tcx>,
         body: &Body<'tcx>,
-        local_names: &IndexVec<Local, Option<Symbol>>,
+        local_names: &IndexSlice<Local, Option<Symbol>>,
         upvars: &[Upvar<'tcx>],
         fr: RegionVid,
     ) -> Option<(Option<Symbol>, Span)> {
@@ -113,7 +113,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     pub(crate) fn get_argument_name_and_span_for_region(
         &self,
         body: &Body<'tcx>,
-        local_names: &IndexVec<Local, Option<Symbol>>,
+        local_names: &IndexSlice<Local, Option<Symbol>>,
         argument_index: usize,
     ) -> (Option<Symbol>, Span) {
         let implicit_inputs = self.universal_regions().defining_ty.implicit_inputs();

compiler/rustc_borrowck/src/lib.rs

@@ -23,7 +23,7 @@ use rustc_errors::{Diagnostic, DiagnosticBuilder, DiagnosticMessage, Subdiagnost
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_index::bit_set::ChunkedBitSet;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_infer::infer::{
     DefiningAnchor, InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin, TyCtxtInferExt,
 };
@@ -154,7 +154,7 @@ fn mir_borrowck(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> &Bor
     let infcx =
         tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(hir_owner.def_id)).build();
     let input_body: &Body<'_> = &input_body.borrow();
-    let promoted: &IndexVec<_, _> = &promoted.borrow();
+    let promoted: &IndexSlice<_, _> = &promoted.borrow();
     let opt_closure_req = do_mir_borrowck(&infcx, input_body, promoted, false).0;
     debug!("mir_borrowck done");
 
@@ -170,7 +170,7 @@ fn mir_borrowck(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> &Bor
 fn do_mir_borrowck<'tcx>(
     infcx: &InferCtxt<'tcx>,
     input_body: &Body<'tcx>,
-    input_promoted: &IndexVec<Promoted, Body<'tcx>>,
+    input_promoted: &IndexSlice<Promoted, Body<'tcx>>,
     return_body_with_facts: bool,
 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
     let def = input_body.source.with_opt_param().as_local().unwrap();
@@ -223,7 +223,7 @@ fn do_mir_borrowck<'tcx>(
     // be modified (in place) to contain non-lexical lifetimes. It
     // will have a lifetime tied to the inference context.
     let mut body_owned = input_body.clone();
-    let mut promoted = input_promoted.clone();
+    let mut promoted = input_promoted.to_owned();
     let free_regions =
         nll::replace_regions_in_mir(&infcx, param_env, &mut body_owned, &mut promoted);
     let body = &body_owned; // no further changes

compiler/rustc_borrowck/src/member_constraints.rs

@@ -2,7 +2,7 @@
 #![deny(rustc::diagnostic_outside_of_impl)]
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxIndexMap;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::infer::MemberConstraint;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::Span;
@@ -215,7 +215,7 @@ where
 /// target_list: A -> B -> C -> D -> E -> F -> (None)
 /// ```
 fn append_list(
-    constraints: &mut IndexVec<NllMemberConstraintIndex, NllMemberConstraint<'_>>,
+    constraints: &mut IndexSlice<NllMemberConstraintIndex, NllMemberConstraint<'_>>,
     target_list: NllMemberConstraintIndex,
     source_list: NllMemberConstraintIndex,
 ) {

compiler/rustc_borrowck/src/nll.rs

@@ -4,7 +4,7 @@
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_hir::def_id::LocalDefId;
-use rustc_index::vec::IndexVec;
+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,
@@ -59,7 +59,7 @@ pub(crate) fn replace_regions_in_mir<'tcx>(
     infcx: &BorrowckInferCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     body: &mut Body<'tcx>,
-    promoted: &mut IndexVec<Promoted, Body<'tcx>>,
+    promoted: &mut IndexSlice<Promoted, Body<'tcx>>,
 ) -> UniversalRegions<'tcx> {
     let def = body.source.with_opt_param().as_local().unwrap();
 
@@ -158,7 +158,7 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
     infcx: &BorrowckInferCtxt<'_, 'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
-    promoted: &IndexVec<Promoted, Body<'tcx>>,
+    promoted: &IndexSlice<Promoted, Body<'tcx>>,
     location_table: &LocationTable,
     param_env: ty::ParamEnv<'tcx>,
     flow_inits: &mut ResultsCursor<'cx, 'tcx, MaybeInitializedPlaces<'cx, 'tcx>>,

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -7,7 +7,7 @@ use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::scc::Sccs;
 use rustc_errors::Diagnostic;
 use rustc_hir::def_id::CRATE_DEF_ID;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_infer::infer::outlives::test_type_match;
 use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound, VerifyIfEq};
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
@@ -399,7 +399,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// the minimum, or narrowest, universe.
     fn compute_scc_universes(
         constraint_sccs: &Sccs<RegionVid, ConstraintSccIndex>,
-        definitions: &IndexVec<RegionVid, RegionDefinition<'tcx>>,
+        definitions: &IndexSlice<RegionVid, RegionDefinition<'tcx>>,
     ) -> IndexVec<ConstraintSccIndex, ty::UniverseIndex> {
         let num_sccs = constraint_sccs.num_sccs();
         let mut scc_universes = IndexVec::from_elem_n(ty::UniverseIndex::MAX, num_sccs);
@@ -486,7 +486,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// more details.
     fn compute_scc_representatives(
         constraints_scc: &Sccs<RegionVid, ConstraintSccIndex>,
-        definitions: &IndexVec<RegionVid, RegionDefinition<'tcx>>,
+        definitions: &IndexSlice<RegionVid, RegionDefinition<'tcx>>,
     ) -> IndexVec<ConstraintSccIndex, ty::RegionVid> {
         let num_sccs = constraints_scc.num_sccs();
         let next_region_vid = definitions.next_index();

compiler/rustc_borrowck/src/renumber.rs

@@ -1,7 +1,7 @@
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
 use crate::BorrowckInferCtxt;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_infer::infer::NllRegionVariableOrigin;
 use rustc_middle::mir::visit::{MutVisitor, TyContext};
 use rustc_middle::mir::Constant;
@@ -16,7 +16,7 @@ use rustc_span::{Span, Symbol};
 pub fn renumber_mir<'tcx>(
     infcx: &BorrowckInferCtxt<'_, 'tcx>,
     body: &mut Body<'tcx>,
-    promoted: &mut IndexVec<Promoted, Body<'tcx>>,
+    promoted: &mut IndexSlice<Promoted, Body<'tcx>>,
 ) {
     debug!(?body.arg_count);
 

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -125,7 +125,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
     infcx: &BorrowckInferCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     body: &Body<'tcx>,
-    promoted: &IndexVec<Promoted, Body<'tcx>>,
+    promoted: &IndexSlice<Promoted, Body<'tcx>>,
     universal_regions: &Rc<UniversalRegions<'tcx>>,
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
@@ -292,7 +292,7 @@ enum FieldAccessError {
 /// is a problem.
 struct TypeVerifier<'a, 'b, 'tcx> {
     cx: &'a mut TypeChecker<'b, 'tcx>,
-    promoted: &'b IndexVec<Promoted, Body<'tcx>>,
+    promoted: &'b IndexSlice<Promoted, Body<'tcx>>,
     last_span: Span,
     errors_reported: bool,
 }
@@ -493,7 +493,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
 impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
     fn new(
         cx: &'a mut TypeChecker<'b, 'tcx>,
-        promoted: &'b IndexVec<Promoted, Body<'tcx>>,
+        promoted: &'b IndexSlice<Promoted, Body<'tcx>>,
     ) -> Self {
         TypeVerifier { promoted, last_span: cx.body.span, cx, errors_reported: false }
     }

compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs

@@ -3,7 +3,7 @@ use rustc_codegen_ssa::debuginfo::{
     wants_c_like_enum_debuginfo,
 };
 use rustc_hir::def::CtorKind;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::IndexSlice;
 use rustc_middle::{
     bug,
     mir::{GeneratorLayout, GeneratorSavedLocal},
@@ -323,7 +323,7 @@ pub fn build_generator_variant_struct_type_di_node<'ll, 'tcx>(
     generator_type_and_layout: TyAndLayout<'tcx>,
     generator_type_di_node: &'ll DIType,
     generator_layout: &GeneratorLayout<'tcx>,
-    state_specific_upvar_names: &IndexVec<GeneratorSavedLocal, Option<Symbol>>,
+    state_specific_upvar_names: &IndexSlice<GeneratorSavedLocal, Option<Symbol>>,
     common_upvar_names: &[String],
 ) -> &'ll DIType {
     let variant_name = GeneratorSubsts::variant_name(variant_index);

compiler/rustc_codegen_ssa/src/coverageinfo/map.rs

@@ -1,6 +1,6 @@
 pub use super::ffi::*;
 
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::mir::coverage::{
     CodeRegion, CounterValueReference, ExpressionOperandId, InjectedExpressionId,
     InjectedExpressionIndex, MappedExpressionIndex, Op,
@@ -205,7 +205,7 @@ impl<'tcx> FunctionCoverage<'tcx> {
         // `expression_index`s lower than the referencing `Expression`. Therefore, it is
         // reasonable to look up the new index of an expression operand while the `new_indexes`
         // vector is only complete up to the current `ExpressionIndex`.
-        let id_to_counter = |new_indexes: &IndexVec<
+        let id_to_counter = |new_indexes: &IndexSlice<
             InjectedExpressionIndex,
             Option<MappedExpressionIndex>,
         >,

compiler/rustc_codegen_ssa/src/mir/analyze.rs

@@ -5,7 +5,7 @@ use super::FunctionCx;
 use crate::traits::*;
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_index::bit_set::BitSet;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_middle::mir::traversal;
 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::{self, Location, TerminatorKind};
@@ -277,7 +277,7 @@ impl CleanupKind {
 /// Recover that structure in an analyze pass.
 pub fn cleanup_kinds(mir: &mir::Body<'_>) -> IndexVec<mir::BasicBlock, CleanupKind> {
     fn discover_masters<'tcx>(
-        result: &mut IndexVec<mir::BasicBlock, CleanupKind>,
+        result: &mut IndexSlice<mir::BasicBlock, CleanupKind>,
         mir: &mir::Body<'tcx>,
     ) {
         for (bb, data) in mir.basic_blocks.iter_enumerated() {
@@ -308,7 +308,10 @@ pub fn cleanup_kinds(mir: &mir::Body<'_>) -> IndexVec<mir::BasicBlock, CleanupKi
         }
     }
 
-    fn propagate<'tcx>(result: &mut IndexVec<mir::BasicBlock, CleanupKind>, mir: &mir::Body<'tcx>) {
+    fn propagate<'tcx>(
+        result: &mut IndexSlice<mir::BasicBlock, CleanupKind>,
+        mir: &mir::Body<'tcx>,
+    ) {
         let mut funclet_succs = IndexVec::from_elem(None, &mir.basic_blocks);
 
         let mut set_successor = |funclet: mir::BasicBlock, succ| match funclet_succs[funclet] {

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -21,7 +21,7 @@ use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::{self, List, TyCtxt, TypeVisitableExt};
 use rustc_span::Span;
 
-use rustc_index::vec::{Idx, IndexVec};
+use rustc_index::vec::{Idx, IndexSlice, IndexVec};
 
 use std::cell::Cell;
 use std::{cmp, iter, mem};
@@ -184,7 +184,7 @@ pub fn collect_temps_and_candidates<'tcx>(
 /// This wraps an `Item`, and has access to all fields of that `Item` via `Deref` coercion.
 struct Validator<'a, 'tcx> {
     ccx: &'a ConstCx<'a, 'tcx>,
-    temps: &'a mut IndexVec<Local, TempState>,
+    temps: &'a mut IndexSlice<Local, TempState>,
 }
 
 impl<'a, 'tcx> std::ops::Deref for Validator<'a, 'tcx> {
@@ -669,7 +669,7 @@ impl<'tcx> Validator<'_, 'tcx> {
 // FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`.
 pub fn validate_candidates(
     ccx: &ConstCx<'_, '_>,
-    temps: &mut IndexVec<Local, TempState>,
+    temps: &mut IndexSlice<Local, TempState>,
     candidates: &[Candidate],
 ) -> Vec<Candidate> {
     let mut validator = Validator { ccx, temps };