HIR: introduce a HirId to DefId map in Definitions

src/librustc/hir/lowering.rs

@@ -392,14 +392,18 @@ impl<'a> LoweringContext<'a> {
                 match tree.kind {
                     UseTreeKind::Simple(_, id1, id2) => {
                         for &id in &[id1, id2] {
-                            self.lctx.resolver.definitions().create_def_with_parent(
+                            let def_index = self.lctx.resolver.definitions().create_def_with_parent(
                                 owner,
                                 id,
+                                None,
                                 DefPathData::Misc,
                                 ExpnId::root(),
                                 tree.prefix.span,
                             );
-                            self.lctx.allocate_hir_id_counter(id);
+                            let hir_id = self.lctx.allocate_hir_id_counter(id);
+
+                            self.lctx.resolver.definitions()
+                                .hir_to_def_index.insert(hir_id, def_index);
                         }
                     }
                     UseTreeKind::Glob => (),
@@ -534,6 +538,10 @@ impl<'a> LoweringContext<'a> {
             .definitions()
             .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
 
+        self.resolver
+            .definitions()
+            .finalize_hir_to_def_index_mapping();
+
         hir::Crate {
             module,
             attrs,
@@ -793,17 +801,20 @@ impl<'a> LoweringContext<'a> {
             ),
         };
 
+        let hir_id = self.lower_node_id(node_id);
+
         // Add a definition for the in-band lifetime def.
         self.resolver.definitions().create_def_with_parent(
             parent_index,
             node_id,
+            Some(hir_id),
             DefPathData::LifetimeNs(str_name),
             ExpnId::root(),
             span,
         );
 
         hir::GenericParam {
-            hir_id: self.lower_node_id(node_id),
+            hir_id,
             name: hir_name,
             attrs: hir_vec![],
             bounds: hir_vec![],
@@ -1095,6 +1106,7 @@ impl<'a> LoweringContext<'a> {
                     self.resolver.definitions().create_def_with_parent(
                         parent_def_index,
                         impl_trait_node_id,
+                        None,
                         DefPathData::ImplTrait,
                         ExpnId::root(),
                         constraint.span,
@@ -1576,6 +1588,7 @@ impl<'a> LoweringContext<'a> {
                     self.context.resolver.definitions().create_def_with_parent(
                         self.parent,
                         def_node_id,
+                        Some(hir_id),
                         DefPathData::LifetimeNs(name.ident().as_interned_str()),
                         ExpnId::root(),
                         lifetime.span);

src/librustc/hir/map/def_collector.rs

@@ -28,7 +28,8 @@ impl<'a> DefCollector<'a> {
                   -> DefIndex {
         let parent_def = self.parent_def;
         debug!("create_def(node_id={:?}, data={:?}, parent_def={:?})", node_id, data, parent_def);
-        self.definitions.create_def_with_parent(parent_def, node_id, data, self.expansion, span)
+        self.definitions.create_def_with_parent(
+            parent_def, node_id, None, data, self.expansion, span)
     }
 
     fn with_parent<F: FnOnce(&mut Self)>(&mut self, parent_def: DefIndex, f: F) {

src/librustc/hir/map/definitions.rs

@@ -8,14 +8,15 @@ use crate::hir;
 use crate::hir::def_id::{CrateNum, DefId, DefIndex, LOCAL_CRATE, CRATE_DEF_INDEX};
 use crate::ich::Fingerprint;
 use crate::session::CrateDisambiguator;
-use crate::util::nodemap::NodeMap;
+use crate::util::nodemap::{HirIdMap, NodeMap};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::indexed_vec::{IndexVec};
 use rustc_data_structures::stable_hasher::StableHasher;
 use std::borrow::Borrow;
 use std::fmt::Write;
 use std::hash::Hash;
+use std::mem;
 use syntax::ast;
 use syntax::ext::hygiene::ExpnId;
 use syntax::symbol::{Symbol, sym, InternedString};
@@ -92,6 +93,10 @@ impl DefPathTable {
 pub struct Definitions {
     table: DefPathTable,
     node_to_def_index: NodeMap<DefIndex>,
+    pub hir_to_def_index: HirIdMap<DefIndex>,
+    /// `DefIndex`es created by `DefCollector::create_def` before the AST lowering; used
+    /// to complete the `hir_to_def_index` mapping afterwards.
+    defs_awaiting_hir_id: NodeMap<DefIndex>,
     def_index_to_node: Vec<ast::NodeId>,
     pub(super) node_to_hir_id: IndexVec<ast::NodeId, hir::HirId>,
     /// If `ExpnId` is an ID of some macro expansion,
@@ -360,11 +365,21 @@ impl Definitions {
         self.node_to_def_index.get(&node).cloned()
     }
 
+    #[inline]
+    pub fn opt_def_index_from_hir_id(&self, hir: hir::HirId) -> Option<DefIndex> {
+        self.hir_to_def_index.get(&hir).cloned()
+    }
+
     #[inline]
     pub fn opt_local_def_id(&self, node: ast::NodeId) -> Option<DefId> {
         self.opt_def_index(node).map(DefId::local)
     }
 
+    #[inline]
+    pub fn opt_local_def_id_from_hir_id(&self, hir: hir::HirId) -> Option<DefId> {
+        self.opt_def_index_from_hir_id(hir).map(DefId::local)
+    }
+
     #[inline]
     pub fn local_def_id(&self, node: ast::NodeId) -> DefId {
         self.opt_local_def_id(node).unwrap()
@@ -440,6 +455,7 @@ impl Definitions {
         assert!(self.def_index_to_node.is_empty());
         self.def_index_to_node.push(ast::CRATE_NODE_ID);
         self.node_to_def_index.insert(ast::CRATE_NODE_ID, root_index);
+        self.hir_to_def_index.insert(hir::CRATE_HIR_ID, root_index);
         self.set_invocation_parent(ExpnId::root(), root_index);
 
         // Allocate some other `DefIndex`es that always must exist.
@@ -452,6 +468,7 @@ impl Definitions {
     pub fn create_def_with_parent(&mut self,
                                   parent: DefIndex,
                                   node_id: ast::NodeId,
+                                  hir_id: Option<hir::HirId>,
                                   data: DefPathData,
                                   expn_id: ExpnId,
                                   span: Span)
@@ -499,6 +516,12 @@ impl Definitions {
         if node_id != ast::DUMMY_NODE_ID {
             debug!("create_def_with_parent: def_index_to_node[{:?} <-> {:?}", index, node_id);
             self.node_to_def_index.insert(node_id, index);
+
+            if let Some(hir_id) = hir_id {
+                self.hir_to_def_index.insert(hir_id, index);
+            } else {
+                self.defs_awaiting_hir_id.insert(node_id, index);
+            }
         }
 
         if expn_id != ExpnId::root() {
@@ -522,6 +545,15 @@ impl Definitions {
         self.node_to_hir_id = mapping;
     }
 
+    /// Fill the missing bits of the `HirId` to `DefIndex` mapping after the AST lowering; see
+    /// the related comment to the `defs_awaiting_hir_id` map in the `Definitions` struct.
+    pub fn finalize_hir_to_def_index_mapping(&mut self) {
+        for (node_id, def_id) in mem::replace(&mut self.defs_awaiting_hir_id, Default::default()) {
+            let hir_id = self.node_to_hir_id[node_id];
+            self.hir_to_def_index.insert(hir_id, def_id);
+        }
+    }
+
     pub fn expansion_that_defined(&self, index: DefIndex) -> ExpnId {
         self.expansions_that_defined.get(&index).cloned().unwrap_or(ExpnId::root())
     }
@@ -611,6 +643,7 @@ macro_rules! define_global_metadata_kind {
                     definitions.create_def_with_parent(
                         CRATE_DEF_INDEX,
                         ast::DUMMY_NODE_ID,
+                        Some(hir::DUMMY_HIR_ID),
                         DefPathData::GlobalMetaData(instance.name().as_interned_str()),
                         ExpnId::root(),
                         DUMMY_SP

src/librustc/hir/map/mod.rs

@@ -281,8 +281,7 @@ impl<'hir> Map<'hir> {
 
     #[inline]
     pub fn opt_local_def_id(&self, hir_id: HirId) -> Option<DefId> {
-        let node_id = self.hir_to_node_id(hir_id);
-        self.definitions.opt_local_def_id(node_id)
+        self.definitions.opt_local_def_id_from_hir_id(hir_id)
     }
 
     #[inline]