Stop using CRATE_DEF_INDEX.

`CRATE_DEF_ID` and `CrateNum::as_def_id` are almost always what we want.

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -1,12 +1,10 @@
 use std::collections::hash_map::Entry::*;
 
 use rustc_ast::expand::allocator::ALLOCATOR_METHODS;
-use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::Node;
-use rustc_index::vec::IndexVec;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::exported_symbols::{
     metadata_symbol_name, ExportedSymbol, SymbolExportLevel,
@@ -277,17 +275,6 @@ fn upstream_monomorphizations_provider(
 
     let mut instances: DefIdMap<FxHashMap<_, _>> = Default::default();
 
-    let cnum_stable_ids: IndexVec<CrateNum, Fingerprint> = {
-        let mut cnum_stable_ids = IndexVec::from_elem_n(Fingerprint::ZERO, cnums.len() + 1);
-
-        for &cnum in cnums.iter() {
-            cnum_stable_ids[cnum] =
-                tcx.def_path_hash(DefId { krate: cnum, index: CRATE_DEF_INDEX }).0;
-        }
-
-        cnum_stable_ids
-    };
-
     let drop_in_place_fn_def_id = tcx.lang_items().drop_in_place_fn();
 
     for &cnum in cnums.iter() {
@@ -316,7 +303,7 @@ fn upstream_monomorphizations_provider(
                     // If there are multiple monomorphizations available,
                     // we select one deterministically.
                     let other_cnum = *e.get();
-                    if cnum_stable_ids[other_cnum] > cnum_stable_ids[cnum] {
+                    if tcx.stable_crate_id(other_cnum) > tcx.stable_crate_id(cnum) {
                         e.insert(cnum);
                     }
                 }

compiler/rustc_hir/src/def.rs

@@ -1,4 +1,4 @@
-use crate::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use crate::def_id::DefId;
 use crate::hir;
 
 use rustc_ast as ast;
@@ -124,9 +124,7 @@ impl DefKind {
     pub fn descr(self, def_id: DefId) -> &'static str {
         match self {
             DefKind::Fn => "function",
-            DefKind::Mod if def_id.index == CRATE_DEF_INDEX && def_id.krate != LOCAL_CRATE => {
-                "crate"
-            }
+            DefKind::Mod if def_id.is_crate_root() && !def_id.is_local() => "crate",
             DefKind::Mod => "module",
             DefKind::Static(..) => "static",
             DefKind::Enum => "enum",

compiler/rustc_hir/src/definitions.rs

@@ -353,11 +353,6 @@ impl Definitions {
         }
     }
 
-    /// Retrieves the root definition.
-    pub fn get_root_def(&self) -> LocalDefId {
-        LocalDefId { local_def_index: CRATE_DEF_INDEX }
-    }
-
     /// Adds a definition with a parent definition.
     pub fn create_def(
         &mut self,

compiler/rustc_hir/src/hir_id.rs

@@ -1,4 +1,4 @@
-use crate::def_id::{LocalDefId, CRATE_DEF_INDEX};
+use crate::def_id::{LocalDefId, CRATE_DEF_ID};
 use std::fmt;
 
 /// Uniquely identifies a node in the HIR of the current crate. It is
@@ -84,8 +84,5 @@ impl ItemLocalId {
     pub const INVALID: ItemLocalId = ItemLocalId::MAX;
 }
 
-/// The `HirId` corresponding to `CRATE_NODE_ID` and `CRATE_DEF_INDEX`.
-pub const CRATE_HIR_ID: HirId = HirId {
-    owner: LocalDefId { local_def_index: CRATE_DEF_INDEX },
-    local_id: ItemLocalId::from_u32(0),
-};
+/// The `HirId` corresponding to `CRATE_NODE_ID` and `CRATE_DEF_ID`.
+pub const CRATE_HIR_ID: HirId = HirId { owner: CRATE_DEF_ID, local_id: ItemLocalId::from_u32(0) };

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -5,7 +5,7 @@ use crate::native_libs;
 
 use rustc_ast as ast;
 use rustc_hir::def::{CtorKind, DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_middle::metadata::ModChild;
 use rustc_middle::middle::exported_symbols::ExportedSymbol;
@@ -324,7 +324,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
                     continue;
                 }
 
-                bfs_queue.push_back(DefId { krate: cnum, index: CRATE_DEF_INDEX });
+                bfs_queue.push_back(cnum.as_def_id());
             }
 
             let mut add_child = |bfs_queue: &mut VecDeque<_>, child: &ModChild, parent: DefId| {

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1633,7 +1633,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             let hir = tcx.hir();
 
             let proc_macro_decls_static = tcx.proc_macro_decls_static(()).unwrap().local_def_index;
-            let stability = tcx.lookup_stability(DefId::local(CRATE_DEF_INDEX));
+            let stability = tcx.lookup_stability(CRATE_DEF_ID);
             let macros =
                 self.lazy(tcx.resolutions(()).proc_macros.iter().map(|p| p.local_def_index));
             let spans = self.tcx.sess.parse_sess.proc_macro_quoted_spans();

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -60,7 +60,7 @@ use crate::mir::mono::MonoItem;
 use crate::ty::TyCtxt;
 
 use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_hir::definitions::DefPathHash;
 use rustc_hir::HirId;
 use rustc_query_system::dep_graph::FingerprintStyle;
@@ -366,7 +366,7 @@ impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for CrateNum {
 
     #[inline(always)]
     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
-        let def_id = DefId { krate: *self, index: CRATE_DEF_INDEX };
+        let def_id = self.as_def_id();
         def_id.to_fingerprint(tcx)
     }
 

compiler/rustc_middle/src/middle/stability.rs

@@ -11,7 +11,7 @@ use rustc_errors::{Applicability, Diagnostic};
 use rustc_feature::GateIssue;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
-use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::{self, HirId};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_session::lint::builtin::{DEPRECATED, DEPRECATED_IN_FUTURE, SOFT_UNSTABLE};
@@ -370,8 +370,7 @@ impl<'tcx> TyCtxt<'tcx> {
             };
         }
 
-        let is_staged_api =
-            self.lookup_stability(DefId { index: CRATE_DEF_INDEX, ..def_id }).is_some();
+        let is_staged_api = self.lookup_stability(def_id.krate.as_def_id()).is_some();
         if !is_staged_api {
             return EvalResult::Allow;
         }

compiler/rustc_middle/src/mir/mod.rs

@@ -15,7 +15,7 @@ use crate::ty::{AdtDef, InstanceDef, Region, ScalarInt, UserTypeAnnotationIndex}
 
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::{CtorKind, Namespace};
-use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
 use rustc_hir::{self, GeneratorKind};
 use rustc_hir::{self as hir, HirId};
 use rustc_session::Session;
@@ -385,7 +385,7 @@ impl<'tcx> Body<'tcx> {
     pub fn new_cfg_only(basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>) -> Self {
         let mut body = Body {
             phase: MirPhase::Built,
-            source: MirSource::item(DefId::local(CRATE_DEF_INDEX)),
+            source: MirSource::item(CRATE_DEF_ID.to_def_id()),
             basic_blocks,
             source_scopes: IndexVec::new(),
             generator: None,

compiler/rustc_middle/src/ty/mod.rs

@@ -36,7 +36,7 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::tagged_ptr::CopyTaggedPtr;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LocalDefIdMap, CRATE_DEF_INDEX};
+use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, LocalDefIdMap, CRATE_DEF_ID};
 use rustc_hir::Node;
 use rustc_macros::HashStable;
 use rustc_query_system::ich::StableHashingContext;
@@ -319,7 +319,7 @@ impl Visibility {
     pub fn from_hir(visibility: &hir::Visibility<'_>, id: hir::HirId, tcx: TyCtxt<'_>) -> Self {
         match visibility.node {
             hir::VisibilityKind::Public => Visibility::Public,
-            hir::VisibilityKind::Crate(_) => Visibility::Restricted(DefId::local(CRATE_DEF_INDEX)),
+            hir::VisibilityKind::Crate(_) => Visibility::Restricted(CRATE_DEF_ID.to_def_id()),
             hir::VisibilityKind::Restricted { ref path, .. } => match path.res {
                 // If there is no resolution, `resolve` will have already reported an error, so
                 // assume that the visibility is public to avoid reporting more privacy errors.
@@ -1992,8 +1992,8 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     fn opt_item_name(self, def_id: DefId) -> Option<Symbol> {
-        if def_id.index == CRATE_DEF_INDEX {
-            Some(self.crate_name(def_id.krate))
+        if let Some(cnum) = def_id.as_crate_root() {
+            Some(self.crate_name(cnum))
         } else {
             let def_key = self.def_key(def_id);
             match def_key.disambiguated_data.data {

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -6,7 +6,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sso::SsoHashSet;
 use rustc_hir as hir;
 use rustc_hir::def::{self, CtorKind, DefKind, Namespace};
-use rustc_hir::def_id::{DefId, DefIdSet, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{DefId, DefIdSet, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::definitions::{DefPathData, DefPathDataName, DisambiguatedDefPathData};
 use rustc_hir::ItemKind;
 use rustc_session::config::TrimmedDefPaths;
@@ -336,9 +336,7 @@ pub trait PrettyPrinter<'tcx>:
 
         // If `def_id` is a direct or injected extern crate, return the
         // path to the crate followed by the path to the item within the crate.
-        if def_id.index == CRATE_DEF_INDEX {
-            let cnum = def_id.krate;
-
+        if let Some(cnum) = def_id.as_crate_root() {
             if cnum == LOCAL_CRATE {
                 return Ok((self.path_crate(cnum)?, true));
             }
@@ -2228,11 +2226,11 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
                     ty::BrNamed(_, _) => br.kind,
                     ty::BrAnon(i) => {
                         let name = region_map[&(i + 1)];
-                        ty::BrNamed(DefId::local(CRATE_DEF_INDEX), name)
+                        ty::BrNamed(CRATE_DEF_ID.to_def_id(), name)
                     }
                     ty::BrEnv => {
                         let name = region_map[&0];
-                        ty::BrNamed(DefId::local(CRATE_DEF_INDEX), name)
+                        ty::BrNamed(CRATE_DEF_ID.to_def_id(), name)
                     }
                 };
                 self.tcx.mk_region(ty::ReLateBound(
@@ -2258,7 +2256,7 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
                             }
                         };
                         do_continue(&mut self, name);
-                        ty::BrNamed(DefId::local(CRATE_DEF_INDEX), name)
+                        ty::BrNamed(CRATE_DEF_ID.to_def_id(), name)
                     }
                 };
                 tcx.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { var: br.var, kind }))
@@ -2693,7 +2691,7 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
     let mut seen_defs: DefIdSet = Default::default();
 
     for &cnum in tcx.crates(()).iter() {
-        let def_id = DefId { krate: cnum, index: CRATE_DEF_INDEX };
+        let def_id = cnum.as_def_id();
 
         // Ignore crates that are not direct dependencies.
         match tcx.extern_crate(def_id) {

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -10,7 +10,6 @@ use crate::ty::{self, InferConst, Lift, Term, Ty, TyCtxt};
 use rustc_data_structures::functor::IdFunctor;
 use rustc_hir as hir;
 use rustc_hir::def::Namespace;
-use rustc_hir::def_id::CRATE_DEF_INDEX;
 use rustc_index::vec::{Idx, IndexVec};
 
 use std::fmt;
@@ -71,7 +70,7 @@ impl fmt::Debug for ty::BoundRegionKind {
         match *self {
             ty::BrAnon(n) => write!(f, "BrAnon({:?})", n),
             ty::BrNamed(did, name) => {
-                if did.index == CRATE_DEF_INDEX {
+                if did.is_crate_root() {
                     write!(f, "BrNamed({})", name)
                 } else {
                     write!(f, "BrNamed({:?}, {})", did, name)

compiler/rustc_monomorphize/src/partitioning/default.rs

@@ -2,7 +2,7 @@ use std::collections::hash_map::Entry;
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def::DefKind;
-use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::definitions::DefPathDataName;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::exported_symbols::SymbolExportLevel;
@@ -335,10 +335,10 @@ fn compute_codegen_unit_name(
     let mut cgu_def_id = None;
     // Walk backwards from the item we want to find the module for.
     loop {
-        if current_def_id.index == CRATE_DEF_INDEX {
+        if current_def_id.is_crate_root() {
             if cgu_def_id.is_none() {
                 // If we have not found a module yet, take the crate root.
-                cgu_def_id = Some(DefId { krate: def_id.krate, index: CRATE_DEF_INDEX });
+                cgu_def_id = Some(def_id.krate.as_def_id());
             }
             break;
         } else if tcx.def_kind(current_def_id) == DefKind::Mod {