Implementation of null-aware operators.

pkg/compiler/lib/src/scanner/scanner.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 scanner;
 
 abstract class Scanner {
   Token tokenize();
 
   factory Scanner(SourceFile file, {bool includeComments: false}) {
@@ skipping 312 matching lines @@
     }
 
     if (identical(next, $SEMICOLON)) {
       appendPrecedenceToken(SEMICOLON_INFO);
       // Type parameters and arguments cannot contain semicolon.
       discardOpenLt();
       return advance();
     }
 
     if (identical(next, $QUESTION)) {
-      appendPrecedenceToken(QUESTION_INFO);
-      return advance();
+      return tokenizeQuestion(next);
     }
 
     if (identical(next, $CLOSE_SQUARE_BRACKET)) {
       return appendEndGroup(CLOSE_SQUARE_BRACKET_INFO,
                             OPEN_SQUARE_BRACKET_TOKEN);
     }
 
     if (identical(next, $BACKPING)) {
       appendPrecedenceToken(BACKPING_INFO);
       return advance();
@@ skipping 98 matching lines @@
     }
     appendBeginGroup(OPEN_SQUARE_BRACKET_INFO);
     return next;
   }
 
   int tokenizeCaret(int next) {
     // ^ ^=
     return select($EQ, CARET_EQ_INFO, CARET_INFO);
   }
 
+  int tokenizeQuestion(int next) {
+    // ? ?. ?? ??=
+    next = advance();
+    if (identical(next, $QUESTION)) {
+      return select($EQ, QUESTION_QUESTION_EQ_INFO, QUESTION_QUESTION_INFO);
+    } else if (identical(next, $PERIOD)) {
+      appendPrecedenceToken(QUESTION_PERIOD_INFO);
+      return advance();
+    } else {
+      appendPrecedenceToken(QUESTION_INFO);
+      return next;
+    }
+  }
+
   int tokenizeBar(int next) {
     // | || |=
     next = advance();
     if (identical(next, $BAR)) {
       appendPrecedenceToken(BAR_BAR_INFO);
       return advance();
     } else if (identical(next, $EQ)) {
       appendPrecedenceToken(BAR_EQ_INFO);
       return advance();
     } else {
@@ skipping 684 matching lines @@
 
 PrecedenceInfo closeBraceInfoFor(BeginGroupToken begin) {
   return const {
     '(': CLOSE_PAREN_INFO,
     '[': CLOSE_SQUARE_BRACKET_INFO,
     '{': CLOSE_CURLY_BRACKET_INFO,
     '<': GT_INFO,
     r'${': CLOSE_CURLY_BRACKET_INFO,
   }[begin.value];
 }