Handle mutually recursive re-exports in dartdocgen

pkg/docgen/lib/src/models/model_helpers.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library docgen.model_helpers;
 
 import 'dart:collection';
 
 import 'package:compiler/src/constants/expressions.dart';
 
@@ skipping 199 matching lines @@
   }
   return map;
 }
 
 /// For the given library determine what items (if any) are exported.
 ///
 /// Returns a Map with three keys: "classes", "methods", and "variables" the
 /// values of which point to a map of exported name identifiers with values
 /// corresponding to the actual DeclarationMirror.
 Map<String, Map<String, DeclarationMirror>> calcExportedItems(
-    LibrarySourceMirror library) {
+    LibrarySourceMirror library, Map visited) {

[tjblasi, 2015/02/19 00:52:55]

It seems a bit strange that this is a required param since non-recursive calls
don't really need to specify it.

I'd put in a weak vote for:
- Have calcExportedItems call _calcExportedItemsRecursive(...) which accepts the
visited map
- Make it an optional positional parameter & check if (visited == null) visited
= {};

Or do nothing, I don't feel strongly about it :)

[Alan Knight, 2015/02/19 01:07:04]

We can't know in advance if it's recursive or not. Or at least not without
re-doing much of the same work. And there are only two callers - the one just
below that passes it through, and the one that starts it all off with the empty
map. So it seemed simplest just to always pass it.

   var exports = {};
+  visited[library] = exports;
   exports['classes'] = new SplayTreeMap();
   exports['methods'] = new SplayTreeMap();
   exports['variables'] = new SplayTreeMap();
 
   // Determine the classes, variables and methods that are exported for a
   // specific dependency.
   void _populateExports(LibraryDependencyMirror export, bool showExport) {
-    var transitiveExports = calcExportedItems(export.targetLibrary);
+    if (visited[export.targetLibrary] != null) return;
+    var transitiveExports = calcExportedItems(export.targetLibrary, visited);
     exports['classes'].addAll(transitiveExports['classes']);
     exports['methods'].addAll(transitiveExports['methods']);
     exports['variables'].addAll(transitiveExports['variables']);
     // If there is a show in the export, add only the show items to the
     // library. Ex: "export foo show bar"
     // Otherwise, add all items, and then remove the hidden ones.
     // Ex: "export foo hide bar"
 
     if (!showExport) {
       // Add all items, and then remove the hidden ones.
@@ skipping 119 matching lines @@
   // the time.
   var sdkLibrary = LIBRARIES[dart2js_util.nameOf(mirror)];
   if (sdkLibrary != null) {
     return !sdkLibrary.documented;
   } else if (dart2js_util.nameOf(mirror).startsWith('_') || dart2js_util.nameOf(
       mirror).contains('._')) {
     return true;
   }
   return false;
 }