Add LineScanner and SpanScanner classes to string_scanner.

pkg/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_maps/source_maps.dart';
+
+import 'exception.dart';
+import 'line_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;
+
+  int get line => _sourceFile.getLine(position);
+  int get column => _sourceFile.getColumn(line, position);
+
+  LineScannerState get state => new _SpanScannerState(this, position);
+
+  set state(LineScannerState state) {
+    if (state is! _SpanScannerState ||
+        !identical((state as _SpanScannerState)._scanner, this)) {
+      throw new ArgumentError("The given LineScannerState was not returned by "
+          "this LineScanner.");
+    }
+
+    this.position = state.position;
+  }
+
+  /// The [Span] 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.
+  Span get lastSpan => _lastSpan;
+  Span _lastSpan;
+
+  /// Returns an empty span at the current location.
+  Span get emptySpan => _sourceFile.span(position);
+
+  /// Creates a new [SpanScanner] that starts scanning from [position].
+  ///
+  /// [sourceUrl] is used as [Location.sourceUrl] for the returned [Span]s as
+  /// well as for error reporting.
+  SpanScanner(String string, sourceUrl, {int position})
+      : _sourceFile = new SourceFile.text(
+            sourceUrl is Uri ? sourceUrl.toString() : sourceUrl, string),
+        super(string, sourceUrl: sourceUrl, position: position);
+
+  /// Creates a [Span] representing the source range between [startState] and
+  /// the current position.
+  Span spanFrom(LineScannerState startState) =>
+      _sourceFile.span(startState.position, position);
+
+  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;
+
+    var span = _sourceFile.span(position, position + length);
+    throw new StringScannerException(message, string, sourceUrl, span);
+  }
+}
+
+/// 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(line, position);
+
+  _SpanScannerState(this._scanner, this.position);
+}