Improve the formatting of strings that contain unprintable ASCII characters.

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',
+  '\x7F': r'\x7F', // delete
 };
 
 /// A [RegExp] that matches whitespace characters that should be escaped.
-final _escapeRegExp =
-    new RegExp("[${_escapeMap.keys.map(_getHexLiteral).join()}]");
+final _escapeRegExp = new RegExp(
+    "[\\x00-\\x07\\x0E-\\x1F${_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].
@@ skipping 11 matching lines @@
   }
 }
 
 /// 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]];
+    var mapped = _escapeMap[match[0]];
+    if (mapped != null) return mapped;
+    return _getHexLiteral(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');
+  return r'\x' + rune.toRadixString(16).toUpperCase().padLeft(2, '0');
 }