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}) {
+  factory Scanner(SourceFile file,
+      {bool includeComments: false, bool enableNullAwareOperators: false}) {
     if (file is Utf8BytesSourceFile) {
-      return new Utf8BytesScanner(file, includeComments: includeComments);
+      return new Utf8BytesScanner(file, includeComments: includeComments,
+          enableNullAwareOperators: enableNullAwareOperators);
     } else {
-      return new StringScanner(file, includeComments: includeComments);
+      return new StringScanner(file, includeComments: includeComments,
+          enableNullAwareOperators: enableNullAwareOperators);
     }
   }
 }
 
 abstract class AbstractScanner implements Scanner {
   // TODO(ahe): Move this class to implementation.
 
   final bool includeComments;
+  final bool enableNullAwareOperators;
 
   /**
    * The string offset for the next token that will be created.
    *
    * Note that in the [Utf8BytesScanner], [stringOffset] and [scanOffset] values
    * are different. One string character can be encoded using multiple UTF-8
    * bytes.
    */
   int tokenStart = -1;
 
@@ skipping 13 matching lines @@
 
   /**
    * The source file that is being scanned. This field can be [:null:].
    * If the source file is available, the scanner assigns its [:lineStarts:] and
    * [:length:] fields at the end of [tokenize].
    */
   final SourceFile file;
 
   final List<int> lineStarts = <int>[0];
 
-  AbstractScanner(this.file, this.includeComments) {
+  AbstractScanner(
+      this.file, this.includeComments, this.enableNullAwareOperators) {
     this.tail = this.tokens;
   }
 
   /**
    * Advances and returns the next character.
    *
    * If the next character is non-ASCII, then the returned value depends on the
    * scanner implementation. The [Utf8BytesScanner] returns a UTF-8 byte, while
    * the [StringScanner] returns a UTF-16 code unit.
    *
@@ skipping 256 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, $QUESTION)) {
+      if (enableNullAwareOperators) {
+        return select($EQ, QUESTION_QUESTION_EQ_INFO, QUESTION_QUESTION_INFO);
+      } else {
+        next = advance();
+        PrecedenceInfo info;
+        if (identical(next, $EQ)) {
+          info = QUESTION_QUESTION_EQ_INFO;
+          next = advance();
+        } else {
+          info = QUESTION_QUESTION_INFO;
+        }
+        appendErrorToken(new UnsupportedNullAwareToken(info.value, tokenStart));
+        return next;
+      }
+    } else if (identical(next, $PERIOD)) {
+      if (enableNullAwareOperators) {
+        appendPrecedenceToken(QUESTION_PERIOD_INFO);
+      } else {
+        appendErrorToken(new UnsupportedNullAwareToken(
+            QUESTION_PERIOD_INFO.value, tokenStart));
+      }
+      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];
 }