Add code to contextualize a span relative to its original source file.

test/util/string_literal_iterator_test.dart

Index: test/util/string_literal_iterator_test.dart
diff --git a/test/util/string_literal_iterator_test.dart b/test/util/string_literal_iterator_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..bd4b56e9ba80abeb5dd6829a4f04fe19ef0a64a9
--- /dev/null
+++ b/test/util/string_literal_iterator_test.dart
@@ -0,0 +1,243 @@
+// Copyright (c) 2015, 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:analyzer/analyzer.dart';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/src/util/string_literal_iterator.dart';
+
+final _offset = "final str = ".length;
+
+void main() {
+  group("returns simple characters in", () {
+    test("a single simple string", () {
+      var iter = _parse('"abc"');
+
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("a"));
+      expect(iter.offset, equals(_offset + 1));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("b"));
+      expect(iter.offset, equals(_offset + 2));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("c"));
+      expect(iter.offset, equals(_offset + 3));
+
+      expect(iter.moveNext(), isFalse);
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 4));
+    });
+
+    test("a raw string", () {
+      var iter = _parse('r"abc"');
+
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 1));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("a"));
+      expect(iter.offset, equals(_offset + 2));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("b"));
+      expect(iter.offset, equals(_offset + 3));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("c"));
+      expect(iter.offset, equals(_offset + 4));
+
+      expect(iter.moveNext(), isFalse);
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 5));
+    });
+
+    test("a multiline string", () {
+      var iter = _parse('"""ab\ncd"""');
+
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 2));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("a"));
+      expect(iter.offset, equals(_offset + 3));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("b"));
+      expect(iter.offset, equals(_offset + 4));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("\n"));
+      expect(iter.offset, equals(_offset + 5));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("c"));
+      expect(iter.offset, equals(_offset + 6));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("d"));
+      expect(iter.offset, equals(_offset + 7));
+
+      expect(iter.moveNext(), isFalse);
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 8));
+    });
+
+    test("a raw multiline string", () {
+      var iter = _parse('r"""ab\ncd"""');
+
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 3));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("a"));
+      expect(iter.offset, equals(_offset + 4));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("b"));
+      expect(iter.offset, equals(_offset + 5));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("\n"));
+      expect(iter.offset, equals(_offset + 6));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("c"));
+      expect(iter.offset, equals(_offset + 7));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("d"));
+      expect(iter.offset, equals(_offset + 8));
+
+      expect(iter.moveNext(), isFalse);
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 9));
+    });
+
+    test("adjacent strings", () {
+      var iter = _parse('"ab" r"cd" """ef\ngh"""');
+
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("a"));
+      expect(iter.offset, equals(_offset + 1));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("b"));
+      expect(iter.offset, equals(_offset + 2));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("c"));
+      expect(iter.offset, equals(_offset + 7));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("d"));
+      expect(iter.offset, equals(_offset + 8));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("e"));
+      expect(iter.offset, equals(_offset + 14));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("f"));
+      expect(iter.offset, equals(_offset + 15));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("\n"));
+      expect(iter.offset, equals(_offset + 16));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("g"));
+      expect(iter.offset, equals(_offset + 17));
+
+      expect(iter.moveNext(), isTrue);
+      expect(iter.current, _isRune("h"));
+      expect(iter.offset, equals(_offset + 18));
+
+      expect(iter.moveNext(), isFalse);
+      expect(iter.current, isNull);
+      expect(iter.offset, equals(_offset + 19));
+    });
+  });
+
+  group("parses an escape sequence for", () {
+    test("a newline", () => _expectEscape(r"\n", "\n"));
+    test("a carriage return", () => _expectEscape(r"\r", "\r"));
+    test("a form feed", () => _expectEscape(r"\f", "\f"));
+    test("a backspace", () => _expectEscape(r"\b", "\b"));
+    test("a tab", () => _expectEscape(r"\t", "\t"));
+    test("a vertical tab", () => _expectEscape(r"\v", "\v"));
+    test("a quote", () => _expectEscape(r'\"', '"'));
+    test("a backslash", () => _expectEscape(r"\\", "\\"));
+
+    test("a hex character", () {
+      _expectEscape(r"\x62", "b");
+      _expectEscape(r"\x7A", "z");
+      _expectEscape(r"\x7a", "z");
+    });
+
+    test("a fixed-length unicode character",
+        () => _expectEscape(r"\u0062", "b"));
+
+    test("a short variable-length unicode character",
+        () => _expectEscape(r"\u{62}", "b"));
+
+    test("a long variable-length unicode character",
+        () => _expectEscape(r"\u{000062}", "b"));
+  });
+
+  group("throws an ArgumentError for", () {
+    test("interpolation", () {
+      expect(() => _parse(r'"$foo"'), throwsArgumentError);
+    });
+
+    test("interpolation in an adjacent string", () {
+      expect(() => _parse(r'"foo" "$bar" "baz"'), throwsArgumentError);
+    });
+  });
+}
+
+/// Asserts that [escape] is parsed as [value].
+void _expectEscape(String escape, String value) {
+  var iter = _parse('"a${escape}b"');
+
+  expect(iter.current, isNull);
+  expect(iter.offset, equals(_offset));
+
+  expect(iter.moveNext(), isTrue);
+  expect(iter.current, _isRune("a"));
+  expect(iter.offset, equals(_offset + 1));
+
+  expect(iter.moveNext(), isTrue);
+  expect(iter.current, _isRune(value));
+  expect(iter.offset, equals(_offset + 2));
+
+  expect(iter.moveNext(), isTrue);
+  expect(iter.current, _isRune("b"));
+  expect(iter.offset, equals(_offset + escape.length + 2));
+
+  expect(iter.moveNext(), isFalse);
+  expect(iter.current, isNull);
+  expect(iter.offset, equals(_offset + escape.length + 3));
+}
+
+/// Returns a matcher that asserts that the given rune is the rune for [char].
+Matcher _isRune(String char) {
+  return predicate((rune) {
+    return rune is int && new String.fromCharCode(rune) == char;
+  }, 'is the rune "$char"');
+}
+
+/// Parses [dart], which should be a string literal, into a
+/// [StringLiteralIterator].
+StringLiteralIterator _parse(String dart) {
+  var literal = parseCompilationUnit("final str = $dart;")
+      .declarations.single.variables.variables.single.initializer;
+  return new StringLiteralIterator(literal);
+}