Update charted to 0.4.8 and roll

packages/string_scanner/lib/src/span_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 string_scanner.span_scanner;
-
 import 'package:source_span/source_span.dart';
 
 import 'eager_span_scanner.dart';
 import 'exception.dart';
 import 'line_scanner.dart';
+import 'relative_span_scanner.dart';
 import 'string_scanner.dart';
 import 'utils.dart';
 
 /// A subclass of [LineScanner] that exposes matched ranges as source map
 /// [Span]s.
 class SpanScanner extends StringScanner implements LineScanner {
   /// The source of the scanner.
   ///
   /// This caches line break information and is used to generate [Span]s.
   final SourceFile _sourceFile;
@@ skipping 10 matching lines @@
           "this LineScanner.");
     }
 
     this.position = state.position;
   }
 
   /// The [FileSpan] for [lastMatch].
   ///
   /// This is the span for the entire match. There's no way to get spans for
   /// subgroups since [Match] exposes no information about their positions.
-  FileSpan get lastSpan => _lastSpan;
+  FileSpan get lastSpan {
+    if (lastMatch == null) _lastSpan = null;
+    return _lastSpan;
+  }
   FileSpan _lastSpan;
 
   /// The current location of the scanner.
   FileLocation get location => _sourceFile.location(position);
 
   /// Returns an empty span at the current location.
   FileSpan get emptySpan => location.pointSpan();
 
   /// Creates a new [SpanScanner] that starts scanning from [position].
   ///
   /// [sourceUrl] is used as [SourceLocation.sourceUrl] for the returned
   /// [FileSpan]s as well as for error reporting. It can be a [String], a
   /// [Uri], or `null`.
   SpanScanner(String string, {sourceUrl, int position})
-      : _sourceFile = new SourceFile(string, url: sourceUrl),
+      : _sourceFile = new SourceFile.fromString(string, url: sourceUrl),
         super(string, sourceUrl: sourceUrl, position: position);
 
   /// Creates a new [SpanScanner] that eagerly computes line and column numbers.
   ///
   /// In general [new SpanScanner] will be more efficient, since it avoids extra
   /// computation on every scan. However, eager scanning can be useful for
   /// situations where the normal course of parsing frequently involves
   /// accessing the current line and column numbers.
   ///
   /// Note that *only* the `line` and `column` fields on the `SpanScanner`
   /// itself and its `LineScannerState` are eagerly computed. To limit their
   /// memory footprint, returned spans and locations will still lazily compute
   /// their line and column numbers.
   factory SpanScanner.eager(String string, {sourceUrl, int position}) =
       EagerSpanScanner;
 
+  /// Creates a new [SpanScanner] that scans within [span].
+  ///
+  /// This scans through [span.text], but emits new spans from [span.file] in
+  /// their appropriate relative positions. The [string] field contains only
+  /// [span.text], and [position], [line], and [column] are all relative to the
+  /// span.
+  factory SpanScanner.within(FileSpan span) = RelativeSpanScanner;
+
   /// Creates a [FileSpan] representing the source range between [startState]
   /// and the current position.
   FileSpan spanFrom(LineScannerState startState, [LineScannerState endState]) {
     var endPosition = endState == null ? position : endState.position;
     return _sourceFile.span(startState.position, endPosition);
   }
 
   bool matches(Pattern pattern) {
     if (!super.matches(pattern)) {
       _lastSpan = null;
       return false;
     }
 
     _lastSpan = _sourceFile.span(position, lastMatch.end);
     return true;
   }
 
   void error(String message, {Match match, int position, int length}) {
     validateErrorArgs(string, match, position, length);
 
     if (match == null && position == null && length == null) match = lastMatch;
     if (position == null) {
       position = match == null ? this.position : match.start;
     }
-    if (length == null) length = match == null ? 1 : match.end - match.start;
+    if (length == null) length = match == null ? 0 : match.end - match.start;
 
     var span = _sourceFile.span(position, position + length);
     throw new StringScannerException(message, span, string);
   }
 }
 
 /// A class representing the state of a [SpanScanner].
 class _SpanScannerState implements LineScannerState {
   /// The [SpanScanner] that created this.
   final SpanScanner _scanner;
 
   final int position;
   int get line => _scanner._sourceFile.getLine(position);
   int get column => _scanner._sourceFile.getColumn(position);
 
   _SpanScannerState(this._scanner, this.position);
 }