Implement the new '??' operator in analyzer.

pkg/analyzer/test/generated/resolver_test.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 engine.resolver_test;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 347 matching lines @@
   void set analysisOptions(AnalysisOptions options) {
     AnalysisOptions currentOptions = analysisOptions;
     bool needsRecompute = currentOptions.analyzeFunctionBodiesPredicate !=
             options.analyzeFunctionBodiesPredicate ||
         currentOptions.generateImplicitErrors !=
             options.generateImplicitErrors ||
         currentOptions.generateSdkErrors != options.generateSdkErrors ||
         currentOptions.dart2jsHint != options.dart2jsHint ||
         (currentOptions.hint && !options.hint) ||
         currentOptions.preserveComments != options.preserveComments ||
+        currentOptions.enableNullAwareOperators !=
+            options.enableNullAwareOperators ||
         currentOptions.enableStrictCallChecks != options.enableStrictCallChecks;
     if (needsRecompute) {
       fail(
           "Cannot set options that cause the sources to be reanalyzed in a test context");
     }
     super.analysisOptions = options;
   }
 
   @override
   bool exists(Source source) =>
@@ skipping 9531 matching lines @@
   }
 
   void test_visitBinaryExpression_equals() {
     // 2 == 3
     Expression node = AstFactory.binaryExpression(
         _resolvedInteger(2), TokenType.EQ_EQ, _resolvedInteger(3));
     expect(_analyze(node), same(_typeProvider.boolType));
     _listener.assertNoErrors();
   }
 
+  void test_visitBinaryExpression_ifNull() {
+    // 1 ?? 1.5
+    Expression node = AstFactory.binaryExpression(
+        _resolvedInteger(1), TokenType.QUESTION_QUESTION, _resolvedDouble(1.5));
+    expect(_analyze(node), same(_typeProvider.numType));
+    _listener.assertNoErrors();
+  }
+
   void test_visitBinaryExpression_logicalAnd() {
     // false && true
     Expression node = AstFactory.binaryExpression(
         AstFactory.booleanLiteral(false), TokenType.AMPERSAND_AMPERSAND,
         AstFactory.booleanLiteral(true));
     expect(_analyze(node), same(_typeProvider.boolType));
     _listener.assertNoErrors();
   }
 
   void test_visitBinaryExpression_logicalOr() {
@@ skipping 3805 matching lines @@
         // check propagated type
         FunctionType propagatedType = node.propagatedType as FunctionType;
         expect(propagatedType.returnType, test.typeProvider.stringType);
       } on AnalysisException catch (e, stackTrace) {
         thrownException[0] = new CaughtException(e, stackTrace);
       }
     }
     return null;
   }
 }