Issue 3968. Support for redirecting factory constructors

compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java

 // 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.
 
 package com.google.dart.compiler.resolver;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Objects;
 import com.google.dart.compiler.DartCompilerContext;
 import com.google.dart.compiler.ErrorCode;
-import com.google.dart.compiler.PackageLibraryManager;
-import com.google.dart.compiler.Source;
 import com.google.dart.compiler.ast.ASTVisitor;
 import com.google.dart.compiler.ast.DartBlock;
 import com.google.dart.compiler.ast.DartClass;
 import com.google.dart.compiler.ast.DartExpression;
 import com.google.dart.compiler.ast.DartField;
 import com.google.dart.compiler.ast.DartFieldDefinition;
 import com.google.dart.compiler.ast.DartFunction;
 import com.google.dart.compiler.ast.DartFunctionTypeAlias;
 import com.google.dart.compiler.ast.DartIdentifier;
 import com.google.dart.compiler.ast.DartMethodDefinition;
@@ skipping 554 matching lines @@
           DartBlock dartBlock = method.getFunction().getBody();
           if (dartBlock != null && !(dartBlock instanceof DartNativeBlock)) {
             resolutionError(method.getName(),
                             ResolverErrorCode.CONST_CONSTRUCTOR_CANNOT_HAVE_BODY);
           }
         }
       }
 
       if (modifiers.isFactory()) {
         if (modifiers.isConstant()) {
-          // Allow const factory ... native ... ; type of constructors, used in core libraries
+          // Allow const factory ... native ... ; type of constructors, used in core libraries.
+          // Allow const factory redirecting.
           DartBlock dartBlock = method.getFunction().getBody();
-          if (dartBlock == null  || !(dartBlock instanceof DartNativeBlock)) {
+          if (!(dartBlock instanceof DartNativeBlock || method.getRedirectedTypeName() != null)) {
             resolutionError(method.getName(), ResolverErrorCode.FACTORY_CANNOT_BE_CONST);
           }
         }
       }
       // TODO(ngeoffray): Add more checks on the modifiers. For
       // example const and missing body.
     }
 
     private void checkConstructor(MethodElement element, DartMethodDefinition method) {
       if (Elements.isNonFactoryConstructor(element) && method.getFunction() != null
@@ skipping 79 matching lines @@
      */
     private void reportDuplicateDeclaration(ErrorCode errorCode, Element element) {
       String name =
           element instanceof MethodElement
               ? Elements.getRawMethodName((MethodElement) element)
               : element.getName();
       resolutionError(element.getNameLocation(), errorCode, name);
     }
   }
 }