rustdoc: Inline items from foreign mods

These were all just previously skipped.

Closes #15648

src/librustdoc/clean/inline.rs

@@ -364,27 +364,33 @@ fn is_doc_hidden(a: &clean::Attribute) -> bool {
 fn build_module(cx: &core::DocContext, tcx: &ty::ctxt,
                 did: ast::DefId) -> clean::Module {
     let mut items = Vec::new();
+    fill_in(cx, tcx, did, &mut items);
+    return clean::Module {
+        items: items,
+        is_crate: false,
+    };
 
     // FIXME: this doesn't handle reexports inside the module itself.
     //        Should they be handled?
+    fn fill_in(cx: &core::DocContext, tcx: &ty::ctxt, did: ast::DefId,
+               items: &mut Vec<clean::Item>) {
         csearch::each_child_of_item(&tcx.sess.cstore, did, |def, _, vis| {
-        if vis != ast::Public { return }
             match def {
-            decoder::DlDef(def) => {
+                decoder::DlDef(def::DefForeignMod(did)) => {
+                    fill_in(cx, tcx, did, items);
+                }
+                decoder::DlDef(def) if vis == ast::Public => {
                     match try_inline_def(cx, tcx, def) {
                         Some(i) => items.extend(i.move_iter()),
                         None => {}
                     }
                 }
+                decoder::DlDef(..) => {}
                 // All impls were inlined above
                 decoder::DlImpl(..) => {}
                 decoder::DlField => fail!("unimplemented field"),
             }
         });
-
-    clean::Module {
-        items: items,
-        is_crate: false,
     }
 }