Refactor the per-module node map `module_children` into a per-resolver map.

src/librustc_resolve/build_reduced_graph.rs

@@ -260,7 +260,7 @@ fn build_reduced_graph_for_item(&mut self, item: &Item, parent_ref: &mut Module<
                 let def = Def::Mod(self.ast_map.local_def_id(item.id));
                 let module = self.new_module(parent_link, Some(def), false, vis);
                 self.define(parent, name, TypeNS, (module, sp));
-                parent.module_children.borrow_mut().insert(item.id, module);
+                self.module_map.insert(item.id, module);
                 *parent_ref = module;
             }
 
@@ -398,7 +398,7 @@ fn build_reduced_graph_for_block(&mut self, block: &Block, parent: &mut Module<'
 
             let parent_link = BlockParentLink(parent, block_id);
             let new_module = self.new_module(parent_link, None, false, parent.vis);
-            parent.module_children.borrow_mut().insert(block_id, new_module);
+            self.module_map.insert(block_id, new_module);
             *parent = new_module;
         }
     }

src/librustc_resolve/lib.rs

@@ -827,22 +827,6 @@ pub struct ModuleS<'a> {
     resolutions: RefCell<HashMap<(Name, Namespace), &'a RefCell<NameResolution<'a>>>>,
     unresolved_imports: RefCell<Vec<&'a ImportDirective<'a>>>,
 
-    // The module children of this node, including normal modules and anonymous modules.
-    // Anonymous children are pseudo-modules that are implicitly created around items
-    // contained within blocks.
-    //
-    // For example, if we have this:
-    //
-    //  fn f() {
-    //      fn g() {
-    //          ...
-    //      }
-    //  }
-    //
-    // There will be an anonymous module created around `g` with the ID of the
-    // entry block for `f`.
-    module_children: RefCell<NodeMap<Module<'a>>>,
-
     prelude: RefCell<Option<Module<'a>>>,
 
     glob_importers: RefCell<Vec<(Module<'a>, &'a ImportDirective<'a>)>>,
@@ -871,7 +855,6 @@ fn new(parent_link: ParentLink<'a>,
             extern_crate_id: None,
             resolutions: RefCell::new(HashMap::new()),
             unresolved_imports: RefCell::new(Vec::new()),
-            module_children: RefCell::new(NodeMap()),
             prelude: RefCell::new(None),
             glob_importers: RefCell::new(Vec::new()),
             globs: RefCell::new((Vec::new())),
@@ -1078,6 +1061,22 @@ pub struct Resolver<'a, 'tcx: 'a> {
     export_map: ExportMap,
     trait_map: TraitMap,
 
+    // A map from nodes to modules, both normal (`mod`) modules and anonymous modules.
+    // Anonymous modules are pseudo-modules that are implicitly created around items
+    // contained within blocks.
+    //
+    // For example, if we have this:
+    //
+    //  fn f() {
+    //      fn g() {
+    //          ...
+    //      }
+    //  }
+    //
+    // There will be an anonymous module created around `g` with the ID of the
+    // entry block for `f`.
+    module_map: NodeMap<Module<'a>>,
+
     // Whether or not to print error messages. Can be set to true
     // when getting additional info for error message suggestions,
     // so as to avoid printing duplicate errors
@@ -1179,6 +1178,7 @@ fn new(session: &'a Session,
             freevars_seen: NodeMap(),
             export_map: NodeMap(),
             trait_map: NodeMap(),
+            module_map: NodeMap(),
             used_imports: HashSet::new(),
             used_crates: HashSet::new(),
 
@@ -1578,7 +1578,8 @@ fn resolve_name_in_module(&mut self,
     fn with_scope<F>(&mut self, id: NodeId, f: F)
         where F: FnOnce(&mut Resolver)
     {
-        if let Some(module) = self.current_module.module_children.borrow().get(&id) {
+        let module = self.module_map.get(&id).cloned(); // clones a reference
+        if let Some(module) = module {
             // Move down in the graph.
             let orig_module = ::std::mem::replace(&mut self.current_module, module);
             self.value_ribs.push(Rib::new(ModuleRibKind(module)));
@@ -2129,8 +2130,7 @@ fn resolve_block(&mut self, block: &Block) {
         debug!("(resolving block) entering block");
         // Move down in the graph, if there's an anonymous module rooted here.
         let orig_module = self.current_module;
-        let anonymous_module =
-            orig_module.module_children.borrow().get(&block.id).map(|module| *module);
+        let anonymous_module = self.module_map.get(&block.id).cloned(); // clones a reference
 
         if let Some(anonymous_module) = anonymous_module {
             debug!("(resolving block) found anonymous module, moving down");