Correctly match and print strings with escaped values

lib/src/util.dart

Index: lib/src/util.dart
diff --git a/lib/src/util.dart b/lib/src/util.dart
index 3ecc47c5846d14842aca546698e828441a676497..a99d2dd1f9fcbedc02722b5349216a2dbc1f260c 100644
--- a/lib/src/util.dart
+++ b/lib/src/util.dart
@@ -7,6 +7,20 @@ 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);
@@ -29,3 +43,20 @@ Matcher wrapMatcher(x) {
     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');
+}