Extract out a source_span package from source_maps.

pkg/source_span/test/location_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:unittest/unittest.dart';
+import 'package:source_span/source_span.dart';
+
+main() {
+  var location;
+  setUp(() {
+    location = new SourceLocation(15,
+        line: 2, column: 6, sourceUrl: "foo.dart");
+  });
+
+  group('errors', () {
+    group('for new SourceLocation()', () {
+      test('offset may not be negative', () {
+        expect(() => new SourceLocation(-1), throwsRangeError);
+      });
+
+      test('line may not be negative', () {
+        expect(() => new SourceLocation(0, line: -1), throwsRangeError);
+      });
+
+      test('column may not be negative', () {
+        expect(() => new SourceLocation(0, column: -1), throwsRangeError);
+      });
+    });
+
+    test('for distance() source URLs must match', () {
+      expect(() => location.distance(new SourceLocation(0)),
+          throwsArgumentError);
+    });
+
+    test('for compareTo() source URLs must match', () {
+      expect(() => location.compareTo(new SourceLocation(0)),
+          throwsArgumentError);
+    });
+  });
+
+  test('fields work correctly', () {
+    expect(location.sourceUrl, equals(Uri.parse("foo.dart")));
+    expect(location.offset, equals(15));
+    expect(location.line, equals(2));
+    expect(location.column, equals(6));
+  });
+
+  group('toolString', () {
+    test('returns a computer-readable representation', () {
+      expect(location.toolString, equals('foo.dart:3:7'));
+    });
+
+    test('gracefully handles a missing source URL', () {
+      var location = new SourceLocation(15, line: 2, column: 6);
+      expect(location.toolString, equals('unknown source:3:7'));
+    });
+  });
+
+  test("distance returns the absolute distance between locations", () {
+    var other = new SourceLocation(10, sourceUrl: "foo.dart");
+    expect(location.distance(other), equals(5));
+    expect(other.distance(location), equals(5));
+  });
+
+  test("pointSpan returns an empty span at location", () {
+    var span = location.pointSpan();
+    expect(span.start, equals(location));
+    expect(span.end, equals(location));
+    expect(span.text, isEmpty);
+  });
+
+  group("compareTo()", () {
+    test("sorts by offset", () {
+      var other = new SourceLocation(20, sourceUrl: "foo.dart");
+      expect(location.compareTo(other), lessThan(0));
+      expect(other.compareTo(location), greaterThan(0));
+    });
+
+    test("considers equal locations equal", () {
+      expect(location.compareTo(location), equals(0));
+    });
+  });
+
+
+  group("equality", () {
+    test("two locations with the same offset and source are equal", () {
+      var other = new SourceLocation(15, sourceUrl: "foo.dart");
+      expect(location, equals(other));
+    });
+
+    test("a different offset isn't equal", () {
+      var other = new SourceLocation(10, sourceUrl: "foo.dart");
+      expect(location, isNot(equals(other)));
+    });
+
+    test("a different source isn't equal", () {
+      var other = new SourceLocation(15, sourceUrl: "bar.dart");
+      expect(location, isNot(equals(other)));
+    });
+  });
+}