Perform indexing during lowering.

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

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`.