Correctly match and print strings with escaped values

lib/src/util.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 matcher.util;
 
 import 'core_matchers.dart';
 import 'interfaces.dart';
 
+/// A [Map] between whitespace characters and their escape sequences.
+const _escapeMap = const {
+  '\n': r'\n',
+  '\r': r'\r',
+  '\f': r'\f',
+  '\b': r'\b',
+  '\t': r'\t',
+  '\v': r'\v',
+};
+
+/// A [RegExp] that matches whitespace characters that should be escaped.
+final _escapeRegExp =
+    new RegExp("[${_escapeMap.keys.map(_getHexLiteral).join()}]");
+
 /// Useful utility for nesting match states.
 void addStateInfo(Map matchState, Map values) {
   var innerState = new Map.from(matchState);
   matchState.clear();
   matchState['state'] = innerState;
   matchState.addAll(values);
 }
 
 /// Takes an argument and returns an equivalent [Matcher].
 ///
 /// If the argument is already a matcher this does nothing,
 /// else if the argument is a function, it generates a predicate
 /// function matcher, else it generates an equals matcher.
 Matcher wrapMatcher(x) {
   if (x is Matcher) {
     return x;
   } else if (x is Function) {
     return predicate(x);
   } else {
     return equals(x);
   }
 }
+
+/// Returns [str] with all whitespace characters represented as their escape
+/// sequences.
+///
+/// Backslash characters are escaped as `\\`
+String escape(String str) {
+  str = str.replaceAll('\\', r'\\');
+  return str.replaceAllMapped(_escapeRegExp, (match) {
+    return _escapeMap[match[0]];
+  });
+}
+
+/// Given single-character string, return the hex-escaped equivalent.
+String _getHexLiteral(String input) {
+  int rune = input.runes.single;
+  return r'\x' + rune.toRadixString(16).padLeft(2, '0');
+}