Perform indexing during lowering.

Do not access DefId<->HirId maps before they are initialized.

compiler/rustc_hir/src/arena.rs

@@ -37,6 +37,7 @@ macro_rules! arena_types {
             [few] llvm_inline_asm: rustc_hir::LlvmInlineAsm<$tcx>,
             [] local: rustc_hir::Local<$tcx>,
             [few] mod_: rustc_hir::Mod<$tcx>,
+            [] owner_info: rustc_hir::OwnerInfo<$tcx>,
             [] param: rustc_hir::Param<$tcx>,
             [] pat: rustc_hir::Pat<$tcx>,
             [] path: rustc_hir::Path<$tcx>,

compiler/rustc_hir/src/hir.rs

@@ -1,5 +1,5 @@
 use crate::def::{CtorKind, DefKind, Res};
-use crate::def_id::{DefId, CRATE_DEF_ID};
+use crate::def_id::DefId;
 crate use crate::hir_id::{HirId, ItemLocalId};
 use crate::LangItem;
 
@@ -663,18 +663,49 @@ pub struct WhereEqPredicate<'hir> {
     pub rhs_ty: &'hir Ty<'hir>,
 }
 
+/// HIR node coupled with its parent's id in the same HIR owner.
+///
+/// The parent is trash when the node is a HIR owner.
+#[derive(Clone, Debug)]
+pub struct ParentedNode<'tcx> {
+    pub parent: ItemLocalId,
+    pub node: Node<'tcx>,
+}
+
 #[derive(Debug)]
-pub struct OwnerInfo<'hir> {
-    pub node: OwnerNode<'hir>,
-    pub attrs: BTreeMap<ItemLocalId, &'hir [Attribute]>,
-    pub bodies: IndexVec<ItemLocalId, Option<&'hir Body<'hir>>>,
-    /// Map indicating what traits are in scope for places where this
-    /// is relevant; generated by resolve.
-    pub trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
+pub struct OwnerNodes<'tcx> {
     /// Pre-computed hash of the full HIR.
     pub hash: Fingerprint,
     /// Pre-computed hash of the top node.
     pub node_hash: Fingerprint,
+    /// Full HIR for the current owner.
+    // The zeroth node's parent is trash, but is never accessed.
+    pub nodes: IndexVec<ItemLocalId, Option<ParentedNode<'tcx>>>,
+    /// Content of local bodies.
+    pub bodies: IndexVec<ItemLocalId, Option<&'tcx Body<'tcx>>>,
+}
+
+#[derive(Debug)]
+pub struct OwnerInfo<'hir> {
+    /// Contents of the HIR.
+    pub nodes: OwnerNodes<'hir>,
+    /// Map from each nested owner to its parent's local id.
+    pub parenting: FxHashMap<LocalDefId, ItemLocalId>,
+
+    pub attrs: BTreeMap<ItemLocalId, &'hir [Attribute]>,
+    /// Map indicating what traits are in scope for places where this
+    /// is relevant; generated by resolve.
+    pub trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
+}
+
+impl<'tcx> OwnerInfo<'tcx> {
+    #[inline]
+    pub fn node(&self) -> OwnerNode<'tcx> {
+        use rustc_index::vec::Idx;
+        let node = self.nodes.nodes[ItemLocalId::new(0)].as_ref().unwrap().node;
+        let node = node.as_owner().unwrap(); // Indexing must ensure it is an OwnerNode.
+        node
+    }
 }
 
 /// The top-level data structure that stores the entire contents of
@@ -688,39 +719,6 @@ pub struct Crate<'hir> {
     pub owners: IndexVec<LocalDefId, Option<OwnerInfo<'hir>>>,
 }
 
-impl Crate<'hir> {
-    pub fn module(&self) -> &'hir Mod<'hir> {
-        let i = self.owners[CRATE_DEF_ID].as_ref().unwrap().node;
-        if let OwnerNode::Crate(m) = i { m } else { panic!() }
-    }
-
-    pub fn item(&self, id: ItemId) -> &'hir Item<'hir> {
-        self.owners[id.def_id].as_ref().unwrap().node.expect_item()
-    }
-
-    pub fn trait_item(&self, id: TraitItemId) -> &'hir TraitItem<'hir> {
-        self.owners[id.def_id].as_ref().unwrap().node.expect_trait_item()
-    }
-
-    pub fn impl_item(&self, id: ImplItemId) -> &'hir ImplItem<'hir> {
-        self.owners[id.def_id].as_ref().unwrap().node.expect_impl_item()
-    }
-
-    pub fn foreign_item(&self, id: ForeignItemId) -> &'hir ForeignItem<'hir> {
-        self.owners[id.def_id].as_ref().unwrap().node.expect_foreign_item()
-    }
-
-    pub fn body(&self, id: BodyId) -> &'hir Body<'hir> {
-        let HirId { owner, local_id } = id.hir_id;
-        self.owners[owner].as_ref().unwrap().bodies[local_id].unwrap()
-    }
-
-    pub fn attrs(&self, id: HirId) -> &'hir [Attribute] {
-        let HirId { owner, local_id } = id;
-        &self.owners[owner].as_ref().unwrap().attrs.get(&local_id).map(|la| *la).unwrap_or(&[])
-    }
-}
-
 /// A block of statements `{ .. }`, which may have a label (in this case the
 /// `targeted_by_break` field will be `true`) and may be `unsafe` by means of
 /// the `rules` being anything but `DefaultBlock`.

compiler/rustc_hir/src/intravisit.rs

@@ -130,6 +130,28 @@ pub trait Map<'hir> {
     fn foreign_item(&self, id: ForeignItemId) -> &'hir ForeignItem<'hir>;
 }
 
+// Used when no map is actually available, forcing manual implementation of nested visitors.
+impl Map<'hir> for ! {
+    fn find(&self, _: HirId) -> Option<Node<'hir>> {
+        unreachable!()
+    }
+    fn body(&self, _: BodyId) -> &'hir Body<'hir> {
+        unreachable!()
+    }
+    fn item(&self, _: ItemId) -> &'hir Item<'hir> {
+        unreachable!()
+    }
+    fn trait_item(&self, _: TraitItemId) -> &'hir TraitItem<'hir> {
+        unreachable!()
+    }
+    fn impl_item(&self, _: ImplItemId) -> &'hir ImplItem<'hir> {
+        unreachable!()
+    }
+    fn foreign_item(&self, _: ForeignItemId) -> &'hir ForeignItem<'hir> {
+        unreachable!()
+    }
+}
+
 /// An erased version of `Map<'hir>`, using dynamic dispatch.
 /// NOTE: This type is effectively only usable with `NestedVisitorMap::None`.
 pub struct ErasedMap<'hir>(&'hir dyn Map<'hir>);

compiler/rustc_hir/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(in_band_lifetimes)]
 #![feature(once_cell)]
 #![feature(min_specialization)]
+#![feature(never_type)]
 #![recursion_limit = "256"]
 
 #[macro_use]

compiler/rustc_hir/src/stable_hash_impls.rs

@@ -1,8 +1,8 @@
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
 
 use crate::hir::{
-    BodyId, Expr, ForeignItem, ForeignItemId, ImplItem, ImplItemId, Item, ItemId, Mod, TraitItem,
-    TraitItemId, Ty, VisibilityKind,
+    BodyId, Expr, ForeignItem, ForeignItemId, ImplItem, ImplItemId, Item, ItemId, Mod, OwnerNodes,
+    TraitItem, TraitItemId, Ty, VisibilityKind,
 };
 use crate::hir_id::{HirId, ItemLocalId};
 use rustc_span::def_id::DefPathHash;
@@ -209,3 +209,12 @@ impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for Item<'_> {
         });
     }
 }
+
+impl<HirCtx: crate::HashStableContext> HashStable<HirCtx> for OwnerNodes<'tcx> {
+    fn hash_stable(&self, hcx: &mut HirCtx, hasher: &mut StableHasher) {
+        // We ignore the `nodes` and `bodies` fields since these refer to information included in
+        // `hash` which is hashed in the collector and used for the crate hash.
+        let OwnerNodes { hash, node_hash: _, nodes: _, bodies: _ } = *self;
+        hash.hash_stable(hcx, hasher);
+    }
+}