dart2js: Handle zero-terminated content explicitly.

pkg/compiler/lib/src/scanner/utf8_bytes_scanner.dart

 // Copyright (c) 2013, 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;
 
 /**
  * Scanner that reads from a UTF-8 encoded list of bytes and creates tokens
  * that points to substrings.
  */
 class Utf8BytesScanner extends ArrayBasedScanner {
-  /** The file content. */
+  /**
+   * The file content.
+   *
+   * The content is zero-terminated.
+   */
   List<int> bytes;
 
   /**
    * Points to the offset of the last byte returned by [advance].
    *
    * After invoking [currentAsUnicode], the [byteOffset] points to the last
    * byte that is part of the (unicode or ASCII) character. That way, [advance]
    * can always increase the byte offset by 1.
    */
   int byteOffset = -1;
@@ skipping 36 matching lines @@
   /**
    * Creates a new Utf8BytesScanner. The source file is expected to be a
    * [Utf8BytesSourceFile] that holds a list of UTF-8 bytes. Otherwise the
    * string text of the source file is decoded.
    *
    * The list of UTF-8 bytes [file.slowUtf8Bytes()] is expected to return an
    * array whose last element is '0' to signal the end of the file. If this
    * is not the case, the entire array is copied before scanning.
    */
   Utf8BytesScanner(SourceFile file, {bool includeComments: false})
-      : bytes = file.slowUtf8Bytes(),
+      : bytes = file.slowUtf8ZeroTerminatedBytes(),
         super(file, includeComments) {
-    ensureZeroTermination();
+    assert(bytes.last == 0);
     // Skip a leading BOM.
     if (_containsBomAt(0)) byteOffset += 3;
   }
 
   /**
    * Creates a new Utf8BytesScanner from a list of UTF-8 bytes.
    *
    * The last element of the list is expected to be '0' to signal the end of
    * the file. If this is not the case, the entire array is copied before
    * scanning.
    */
-  Utf8BytesScanner.fromBytes(this.bytes, {bool includeComments: false})
-      : super(null, includeComments) {
-    ensureZeroTermination();
-  }
-
-  void ensureZeroTermination() {
-    if (bytes.isEmpty || bytes[bytes.length - 1] != 0) {
-      // TODO(lry): abort instead of copying the array, or warn?
-      var newBytes =  new Uint8List(bytes.length + 1);
-      for (int i = 0; i < bytes.length; i++) {
-        newBytes[i] = bytes[i];
-      }
-      newBytes[bytes.length] = 0;
-      bytes = newBytes;
-    }
+  Utf8BytesScanner.fromBytes(List<int> zeroTerminatedBytes,
+                             {bool includeComments: false})
+      : this.bytes = zeroTerminatedBytes,
+        super(null, includeComments) {
+    assert(bytes.last == 0);
   }
 
   bool _containsBomAt(int offset) {
     const BOM_UTF8 = const [0xEF, 0xBB, 0xBF];
 
     return offset + 3 < bytes.length &&
         bytes[offset] == BOM_UTF8[0] &&
         bytes[offset + 1] == BOM_UTF8[1] &&
         bytes[offset + 2] == BOM_UTF8[2];
   }
@@ skipping 96 matching lines @@
 
   void appendSubstringToken(PrecedenceInfo info, int start, bool asciiOnly,
                             [int extraOffset = 0]) {
     tail.next = new StringToken.fromUtf8Bytes(
         info, bytes, start, byteOffset + extraOffset, asciiOnly, tokenStart);
     tail = tail.next;
   }
 
   bool atEndOfFile() => byteOffset >= bytes.length - 1;
 }