Only store a LocalDefId in hir::ForeignItem.

compiler/rustc_metadata/src/foreign_modules.rs

@@ -4,25 +4,23 @@ use rustc_middle::middle::cstore::ForeignModule;
 use rustc_middle::ty::TyCtxt;
 
 crate fn collect(tcx: TyCtxt<'_>) -> Vec<ForeignModule> {
-    let mut collector = Collector { tcx, modules: Vec::new() };
+    let mut collector = Collector { modules: Vec::new() };
     tcx.hir().krate().visit_all_item_likes(&mut collector);
     collector.modules
 }
 
-struct Collector<'tcx> {
-    tcx: TyCtxt<'tcx>,
+struct Collector {
     modules: Vec<ForeignModule>,
 }
 
-impl ItemLikeVisitor<'tcx> for Collector<'tcx> {
+impl ItemLikeVisitor<'tcx> for Collector {
     fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
         let items = match it.kind {
             hir::ItemKind::ForeignMod { items, .. } => items,
             _ => return,
         };
 
-        let foreign_items =
-            items.iter().map(|it| self.tcx.hir().local_def_id(it.id.hir_id).to_def_id()).collect();
+        let foreign_items = items.iter().map(|it| it.id.def_id.to_def_id()).collect();
         self.modules.push(ForeignModule { foreign_items, def_id: it.def_id.to_def_id() });
     }