Emit classes that are only referenced by type literals.

sdk/lib/_internal/compiler/implementation/dart_backend/backend.dart

 // Copyright (c) 2012, 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.
 
 part of dart_backend;
 
 // TODO(ahe): This class is simply wrong.  This backend should use
 // elements when it can, not AST nodes.  Perhaps a [Map<Element,
 // TreeElements>] is what is needed.
 class ElementAst {
@@ skipping 27 matching lines @@
   /// Initialized when dart:mirrors is loaded if the useMirrorHelperLibrary
   /// field is set.
   FunctionElement mirrorHelperGetNameFunction;
   /// Initialized when dart:mirrors is loaded if the useMirrorHelperLibrary
   /// field is set.
   Element mirrorHelperSymbolsMap;
 
   Map<Element, TreeElements> get resolvedElements =>
       compiler.enqueuer.resolution.resolvedElements;
 
+  final Set<ClassElement> usedTypeLiterals = new Set<ClassElement>();
+
   /**
    * Tells whether it is safe to remove type declarations from variables,
    * functions parameters. It becomes not safe if:
    * 1) TypeError is used somewhere in the code,
    * 2) The code has typedefs in right hand side of IS checks,
    * 3) The code has classes which extend typedefs, have type arguments typedefs
    *    or type variable bounds typedefs.
    * These restrictions can be less strict.
    */
   bool isSafeToRemoveTypeDeclarations(
@@ skipping 232 matching lines @@
         assert(shouldOutput(enclosingClass));
         addClass(enclosingClass);
         classMembers[enclosingClass].add(element);
         processElement(element, elementAst);
       } else {
         if (element.isTopLevel()) {
           addTopLevel(element, elementAst);
         }
       }
     });
+    Set<ClassElement> emitNoMembersFor = new Set<ClassElement>();
+    usedTypeLiterals.forEach((ClassElement element) {
+      if (shouldOutput(element)) {
+        if (!topLevelElements.contains(element)) {
+          // The class is only referenced by type literals.
+          emitNoMembersFor.add(element);
+        }
+        addClass(element);
+      }
+    });
 
     // Add synthesized constructors to classes with no resolved constructors,
     // but which originally had any constructor.  That should prevent
     // those classes from being instantiable with default constructor.
     Identifier synthesizedIdentifier = new Identifier(
         new StringToken.fromString(IDENTIFIER_INFO, '', -1));
 
     NextClassElement:
     for (ClassElement classElement in classMembers.keys) {
+      if (emitNoMembersFor.contains(classElement)) continue;
       for (Element member in classMembers[classElement]) {
         if (member.isConstructor()) continue NextClassElement;
       }
       if (classElement.constructors.isEmpty) continue NextClassElement;
 
       // TODO(antonm): check with AAR team if there is better approach.
       // As an idea: provide template as a Dart code---class C { C.name(); }---
       // and then overwrite necessary parts.
       var classNode = classElement.parseNode(compiler);
       SynthesizedConstructorElementX constructor =
@@ skipping 55 matching lines @@
     if (outputAst) {
       // TODO(antonm): Ideally XML should be a separate backend.
       // TODO(antonm): obey renames and minification, at least as an option.
       StringBuffer sb = new StringBuffer();
       outputElement(element) {
         sb.write(element.parseNode(compiler).toDebugString());
       }
 
       // Emit XML for AST instead of the program.
       for (final topLevel in sortedTopLevels) {
-        if (topLevel.isClass()) {
+        if (topLevel.isClass() && !emitNoMembersFor.contains(topLevel)) {
           // TODO(antonm): add some class info.
           sortedClassMembers[topLevel].forEach(outputElement);
         } else {
           outputElement(topLevel);
         }
       }
       compiler.assembledCode = '<Program>\n$sb</Program>\n';
       return;
     }
 
@@ skipping 51 matching lines @@
         mirrorHelperLibrary = element;
         mirrorHelperGetNameFunction = mirrorHelperLibrary.find(
             MirrorRenamer.MIRROR_HELPER_GET_NAME_FUNCTION);
         mirrorHelperSymbolsMap = mirrorHelperLibrary.find(
             MirrorRenamer.MIRROR_HELPER_SYMBOLS_MAP_NAME);
       });
     }
     return new Future.value();
   }
 
+  void registerTypeLiteral(Element element,
+                           Enqueuer enqueuer,
+                           TreeElements elements) {
+    if (element.isClass()) {
+      usedTypeLiterals.add(element);
+    }
+  }
+
   void registerStaticSend(Element element, Node node) {
     if (useMirrorHelperLibrary) {
       mirrorRenamer.registerStaticSend(element, node);
     }
   }
 
   void registerMirrorHelperElement(Element element, Node node) {
     if (mirrorHelperLibrary != null
         && element.getLibrary() == mirrorHelperLibrary) {
       mirrorRenamer.registerHelperElement(element, node);
@@ skipping 87 matching lines @@
 }
 
 compareElements(e0, e1) {
   int result = compareBy((e) => e.getLibrary().canonicalUri.toString())(e0, e1);
   if (result != 0) return result;
   return compareBy((e) => e.position().charOffset)(e0, e1);
 }
 
 List<Element> sortElements(Iterable<Element> elements) =>
     sorted(elements, compareElements);