Add LineScanner and SpanScanner classes to string_scanner.

pkg/string_scanner/lib/string_scanner.dart

Index: pkg/string_scanner/lib/string_scanner.dart
diff --git a/pkg/string_scanner/lib/string_scanner.dart b/pkg/string_scanner/lib/string_scanner.dart
index 3e3913b50169ba5796102c6314aba658341457b8..be294f4f651d8be72bdcfe78353ca12554dab99c 100644
--- a/pkg/string_scanner/lib/string_scanner.dart
+++ b/pkg/string_scanner/lib/string_scanner.dart
@@ -5,165 +5,7 @@
 /// A library for parsing strings using a sequence of patterns.
 library string_scanner;
 
-import 'dart:math' as math;
-
-/// When compiled to JS, forward slashes are always escaped in [RegExp.pattern].
-///
-/// See issue 17998.
-final _slashAutoEscape = new RegExp("/").pattern == "\\/";
-
-// TODO(nweiz): Add some integration between this and source maps.
-/// A class that scans through a string using [Pattern]s.
-class StringScanner {
-  /// The string being scanned through.
-  final String string;
-
-  /// The current position of the scanner in the string, in characters.
-  int get position => _position;
-  set position(int position) {
-    if (position < 0 || position > string.length) {
-      throw new ArgumentError("Invalid position $position");
-    }
-
-    _position = position;
-  }
-  int _position = 0;
-
-  /// The data about the previous match made by the scanner.
-  ///
-  /// If the last match failed, this will be `null`.
-  Match get lastMatch => _lastMatch;
-  Match _lastMatch;
-
-  /// The portion of the string that hasn't yet been scanned.
-  String get rest => string.substring(position);
-
-  /// Whether the scanner has completely consumed [string].
-  bool get isDone => position == string.length;
-
-  /// Creates a new [StringScanner] that starts scanning from [position].
-  ///
-  /// [position] defaults to 0, the beginning of the string.
-  StringScanner(this.string, {int position}) {
-    if (position != null) this.position = position;
-  }
-
-  /// If [pattern] matches at the current position of the string, scans forward
-  /// until the end of the match.
-  ///
-  /// Returns whether or not [pattern] matched.
-  bool scan(Pattern pattern) {
-    var success = matches(pattern);
-    if (success) _position = _lastMatch.end;
-    return success;
-  }
-
-  /// If [pattern] matches at the current position of the string, scans forward
-  /// until the end of the match.
-  ///
-  /// If [pattern] did not match, throws a [FormatException] describing the
-  /// position of the failure. [name] is used in this error as the expected name
-  /// of the pattern being matched; if it's `null`, the pattern itself is used
-  /// instead.
-  void expect(Pattern pattern, {String name}) {
-    if (scan(pattern)) return;
-
-    if (name == null) {
-      if (pattern is RegExp) {
-        var source = pattern.pattern;
-        if (!_slashAutoEscape) source = source.replaceAll("/", "\\/");
-        name = "/$source/";
-      } else {
-        name = pattern.toString()
-            .replaceAll("\\", "\\\\").replaceAll('"', '\\"');
-        name = '"$name"';
-      }
-    }
-    _fail(name);
-  }
-
-  /// If the string has not been fully consumed, this throws a
-  /// [FormatException].
-  void expectDone() {
-    if (isDone) return;
-    _fail("no more input");
-  }
-
-  /// Returns whether or not [pattern] matches at the current position of the
-  /// string.
-  ///
-  /// This doesn't move the scan pointer forward.
-  bool matches(Pattern pattern) {
-    _lastMatch = pattern.matchAsPrefix(string, position);
-    return _lastMatch != null;
-  }
-
-  /// Throws a [FormatException] with [message] as well as a detailed
-  /// description of the location of the error in the string.
-  ///
-  /// [match] is the match information for the span of the string with which the
-  /// error is associated. This should be a match returned by this scanner's
-  /// [lastMatch] property. By default, the error is associated with the last
-  /// match.
-  ///
-  /// If [position] and/or [length] are passed, they are used as the error span
-  /// instead. If only [length] is passed, [position] defaults to the current
-  /// position; if only [position] is passed, [length] defaults to 1.
-  ///
-  /// It's an error to pass [match] at the same time as [position] or [length].
-  void error(String message, {Match match, int position, int length}) {
-    if (match != null && (position != null || length != null)) {
-      throw new ArgumentError("Can't pass both match and position/length.");
-    }
-
-    if (position != null && position < 0) {
-      throw new RangeError("position must be greater than or equal to 0.");
-    }
-
-    if (length != null && length < 1) {
-      throw new RangeError("length must be greater than or equal to 0.");
-    }
-
-    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;
-
-    var newlines = "\n".allMatches(string.substring(0, position)).toList();
-    var line = newlines.length + 1;
-    var column;
-    var lastLine;
-    if (newlines.isEmpty) {
-      column = position + 1;
-      lastLine = string.substring(0, position);
-    } else {
-      column = position - newlines.last.end + 1;
-      lastLine = string.substring(newlines.last.end, position);
-    }
-
-    var remaining = string.substring(position);
-    var nextNewline = remaining.indexOf("\n");
-    if (nextNewline == -1) {
-      lastLine += remaining;
-    } else {
-      length = math.min(length, nextNewline);
-      lastLine += remaining.substring(0, nextNewline);
-    }
-
-    var spaces = new List.filled(column - 1, ' ').join();
-    var underline = new List.filled(length, '^').join();
-
-    throw new FormatException(
-        "Error on line $line, column $column: $message\n"
-        "$lastLine\n"
-        "$spaces$underline");
-  }
-
-  // TODO(nweiz): Make this handle long lines more gracefully.
-  /// Throws a [FormatException] describing that [name] is expected at the
-  /// current position in the string.
-  void _fail(String name) {
-    error("expected $name.", position: this.position, length: 1);
-  }
-}
+export 'src/exception.dart';
+export 'src/line_scanner.dart';
+export 'src/span_scanner.dart';
+export 'src/string_scanner.dart';