Implement the new '??' operator in analyzer.

pkg/analyzer/lib/src/generated/incremental_scanner.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.incremental_scanner;
 
 import "dart:math" as math;
 
+import 'package:analyzer/src/generated/engine.dart';
+
 import 'error.dart';
 import 'scanner.dart';
 import 'source.dart';
 import 'utilities_collection.dart' show TokenMap;
 
 /**
  * An `IncrementalScanner` is a scanner that scans a subset of a string and
  * inserts the resulting tokens into the middle of an existing token stream.
  */
 class IncrementalScanner {
   /**
    * The source being scanned.
    */
   final Source source;
 
   /**
    * The reader used to access the characters in the source.
    */
   final CharacterReader reader;
 
   /**
    * The error listener that will be informed of any errors that are found
    * during the scan.
    *
    * TODO(brianwilkerson) Replace this with a list of errors so that we can
    * update the errors.
    */
   final AnalysisErrorListener errorListener;
 
+  final AnalysisOptions _options;
+
   /**
    * A map from tokens that were copied to the copies of the tokens.
    */
   TokenMap _tokenMap = new TokenMap();
 
   /**
    * The token immediately to the left of the range of tokens that were
    * modified.
    */
   Token leftToken;
 
   /**
    * The token immediately to the right of the range of tokens that were
    * modified.
    */
   Token rightToken;
 
   /**
    * A flag indicating whether there were any non-comment tokens changed (other
    * than having their position updated) as a result of the modification.
    */
   bool hasNonWhitespaceChange = false;
 
   /**
    * Initialize a newly created scanner to scan characters within the given
    * [source]. The content of the source can be read using the given [reader].
    * Any errors that are found will be reported to the given [errorListener].
+   * [_options] will determine how scanning is to be performed.
    */
-  IncrementalScanner(this.source, this.reader, this.errorListener);
+  IncrementalScanner(
+      this.source, this.reader, this.errorListener, this._options);
 
   /**
    * Return a map from tokens that were copied to the copies of the tokens.
    *
    * @return a map from tokens that were copied to the copies of the tokens
    */
   TokenMap get tokenMap => _tokenMap;
 
   /**
    * Given the [stream] of tokens scanned from the original source, the modified
@@ skipping 134 matching lines @@
     return token;
   }
 
   /**
    * Scan the token between the [start] (inclusive) and [end] (exclusive)
    * offsets.
    */
   Token _scanRange(int start, int end) {
     Scanner scanner = new Scanner(
         source, new CharacterRangeReader(reader, start, end), errorListener);
+    scanner.enableNullAwareOperators = _options.enableNullAwareOperators;
     return scanner.tokenize();
   }
 
   /**
    * Update the offsets of every token from the given [token] to the end of the
    * stream by adding the given [delta].
    */
   void _updateOffsets(Token token, int delta) {
     while (token.type != TokenType.EOF) {
       _tokenMap.put(token, token);
       token.offset += delta;
       Token comment = token.precedingComments;
       while (comment != null) {
         comment.offset += delta;
         comment = comment.next;
       }
       token = token.next;
     }
     _tokenMap.put(token, token);
     token.offset += delta;
   }
 }