Add SpanScanner.within().

test/span_scanner_test.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.
 
+import 'package:source_span/source_span.dart';
 import 'package:string_scanner/string_scanner.dart';
 import 'package:test/test.dart';
 
+import 'utils.dart';
+
 void main() {
   testForImplementation("lazy", () {
     return new SpanScanner('foo\nbar\nbaz', sourceUrl: 'source');
   });
 
   testForImplementation("eager", () {
     return new SpanScanner.eager('foo\nbar\nbaz', sourceUrl: 'source');
   });
+
+  group("within", () {
+    var text = 'first\nbefore: foo\nbar\nbaz :after\nlast';
+    var startOffset = text.indexOf('foo');
+
+    var scanner;
+    setUp(() {
+      var file = new SourceFile(text, url: 'source');
+      scanner = new SpanScanner.within(
+          file.span(startOffset, text.indexOf(' :after')));
+    });
+
+    test("string only includes the span text", () {
+      expect(scanner.string, equals("foo\nbar\nbaz"));
+    });
+
+    test("line and column are span-relative", () {
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(0));
+
+      scanner.scan("foo");
+      expect(scanner.line, equals(0));
+      expect(scanner.column, equals(3));
+
+      scanner.scan("\n");
+      expect(scanner.line, equals(1));
+      expect(scanner.column, equals(0));
+    });
+
+    test("tracks the span for the last match", () {
+      scanner.scan('fo');
+      scanner.scan('o\nba');
+
+      var span = scanner.lastSpan;
+      expect(span.start.offset, equals(startOffset + 2));
+      expect(span.start.line, equals(1));
+      expect(span.start.column, equals(10));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.end.offset, equals(startOffset + 6));
+      expect(span.end.line, equals(2));
+      expect(span.end.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.text, equals('o\nba'));
+    });
+
+    test(".spanFrom() returns a span from a previous state", () {
+      scanner.scan('fo');
+      var state = scanner.state;
+      scanner.scan('o\nba');
+      scanner.scan('r\nba');
+
+      var span = scanner.spanFrom(state);
+      expect(span.text, equals('o\nbar\nba'));
+    });
+
+    test(".emptySpan returns an empty span at the current location", () {
+      scanner.scan('foo\nba');
+
+      var span = scanner.emptySpan;
+      expect(span.start.offset, equals(startOffset + 6));
+      expect(span.start.line, equals(2));
+      expect(span.start.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.end.offset, equals(startOffset + 6));
+      expect(span.end.line, equals(2));
+      expect(span.end.column, equals(2));
+      expect(span.start.sourceUrl, equals(Uri.parse('source')));
+
+      expect(span.text, equals(''));
+    });
+
+    test(".error() uses an absolute span", () {
+      scanner.expect("foo");
+      expect(() => scanner.error('oh no!'),
+          throwsStringScannerException("foo"));
+    });
+
+    test(".isDone returns true at the end of the span", () {
+      scanner.expect("foo\nbar\nbaz");
+      expect(scanner.isDone, isTrue);
+    });
+  });
 }
 
 void testForImplementation(String name, SpanScanner create()) {
   group("for a $name scanner", () {
     var scanner;
     setUp(() => scanner = create());
 
     test("tracks the span for the last match", () {
       scanner.scan('fo');
       scanner.scan('o\nba');
@@ skipping 33 matching lines @@
 
       expect(span.end.offset, equals(6));
       expect(span.end.line, equals(1));
       expect(span.end.column, equals(2));
       expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
       expect(span.text, equals(''));
     });
   });
 }