rustc: don't recurse through nested items in decoded HIR fragments.

src/librustc/hir/map/collector.rs

@@ -27,6 +27,10 @@ pub struct NodeCollector<'ast> {
     pub map: Vec<MapEntry<'ast>>,
     /// The parent of this node
     pub parent_node: NodeId,
+    /// If true, completely ignore nested items. We set this when loading
+    /// HIR from metadata, since in that case we only want the HIR for
+    /// one specific item (and not the ones nested inside of it).
+    pub ignore_nested_items: bool
 }
 
 impl<'ast> NodeCollector<'ast> {
@@ -35,6 +39,7 @@ impl<'ast> NodeCollector<'ast> {
             krate: krate,
             map: vec![],
             parent_node: CRATE_NODE_ID,
+            ignore_nested_items: false
         };
         collector.insert_entry(CRATE_NODE_ID, RootCrate);
 
@@ -52,6 +57,7 @@ impl<'ast> NodeCollector<'ast> {
             krate: krate,
             map: map,
             parent_node: parent_node,
+            ignore_nested_items: true
         };
 
         assert_eq!(parent_def_path.krate, parent_def_id.krate);
@@ -88,7 +94,9 @@ impl<'ast> Visitor<'ast> for NodeCollector<'ast> {
     /// their outer items.
     fn visit_nested_item(&mut self, item: ItemId) {
         debug!("visit_nested_item: {:?}", item);
-        self.visit_item(self.krate.item(item.id))
+        if !self.ignore_nested_items {
+            self.visit_item(self.krate.item(item.id))
+        }
     }
 
     fn visit_item(&mut self, i: &'ast Item) {

src/librustc/hir/map/def_collector.rs

@@ -285,15 +285,6 @@ impl<'ast> visit::Visitor for DefCollector<'ast> {
 
 // We walk the HIR rather than the AST when reading items from metadata.
 impl<'ast> intravisit::Visitor<'ast> for DefCollector<'ast> {
-    /// Because we want to track parent items and so forth, enable
-    /// deep walking so that we walk nested items in the context of
-    /// their outer items.
-    fn visit_nested_item(&mut self, item_id: hir::ItemId) {
-        debug!("visit_nested_item: {:?}", item_id);
-        let item = self.hir_crate.unwrap().item(item_id.id);
-        self.visit_item(item)
-    }
-
     fn visit_item(&mut self, i: &'ast hir::Item) {
         debug!("visit_item: {:?}", i);
 

src/test/run-pass/auxiliary/issue-17718-aux.rs

@@ -14,11 +14,10 @@ use std::sync::atomic;
 
 pub const C1: usize = 1;
 pub const C2: atomic::AtomicUsize = atomic::AtomicUsize::new(0);
-pub const C3: fn() = foo;
+pub const C3: fn() = { fn foo() {} foo };
 pub const C4: usize = C1 * C1 + C1 / C1;
 pub const C5: &'static usize = &C4;
 
 pub static S1: usize = 3;
 pub static S2: atomic::AtomicUsize = atomic::AtomicUsize::new(0);
 
-fn foo() {}