Implement the new '??=' operator in analyzer.

pkg/analyzer/test/generated/non_error_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.non_error_resolver_test;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/parser.dart' show ParserErrorCode;
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:unittest/unittest.dart' as _ut;
 
 import '../reflective_tests.dart';
 import 'resolver_test.dart';
 import 'test_support.dart';
 
 main() {
@@ skipping 2281 matching lines @@
 
   void test_invalidAssignment_defaultValue_optional() {
     Source source = addSource(r'''
 f([String x = '0']) {
 }''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
 
+  void test_invalidAssignment_ifNullAssignment_compatibleType() {
+    AnalysisOptionsImpl options = new AnalysisOptionsImpl();
+    options.enableNullAwareOperators = true;
+    resetWithOptions(options);
+    Source source = addSource('''
+void f(int i) {
+  num n;
+  n ??= i;
+}
+''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
+  void test_invalidAssignment_ifNullAssignment_sameType() {
+    AnalysisOptionsImpl options = new AnalysisOptionsImpl();
+    options.enableNullAwareOperators = true;
+    resetWithOptions(options);
+    Source source = addSource('''
+void f(int i) {
+  int j;
+  j ??= i;
+}
+''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_invalidAssignment_implicitlyImplementFunctionViaCall_1() {
     // 18341
     //
     // This test and
     // 'test_invalidAssignment_implicitlyImplementFunctionViaCall_2()'
     // are closely related: here we see that 'I' checks as a subtype of
     // 'IntToInt'.
     Source source = addSource(r'''
 class I {
   int call(int x) => 0;
@@ skipping 3071 matching lines @@
     resolve(source);
     assertNoErrors(source);
     verify([source]);
     reset();
   }
 
   void _check_wrongNumberOfParametersForOperator1(String name) {
     _check_wrongNumberOfParametersForOperator(name, "a");
   }
 }