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// 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.
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;
int get line => _sourceFile.getLine(position);
int get column => _sourceFile.getColumn(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 [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 {
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),
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}) =
/// 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 ? 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);