Make Error.safeToString convert control codes in strings to escapes.

sdk/lib/core/errors.dart

Index: sdk/lib/core/errors.dart
diff --git a/sdk/lib/core/errors.dart b/sdk/lib/core/errors.dart
index f61cdfe07f815bcdc596f8851d782cd77d486edc..1fb0b3546b1d51b29b0aaff434cef7caa9b3698f 100644
--- a/sdk/lib/core/errors.dart
+++ b/sdk/lib/core/errors.dart
@@ -16,15 +16,48 @@ class Error {
       return object.toString();
     }
     if (object is String) {
-      // TODO(ahe): Remove backslash when http://dartbug.com/4995 is fixed.
       String string = object;
-      const backslash = '\\';
-      String escaped = string
-        .replaceAll('$backslash', '$backslash$backslash')
-        .replaceAll('\n', '${backslash}n')
-        .replaceAll('\r', '${backslash}r')
-        .replaceAll('"',  '$backslash"');
-      return '"$escaped"';
+      StringBuffer buffer = new StringBuffer('"');
+      const int TAB = 0x09;
+      const int NEWLINE = 0x0a;
+      const int CARRIGE_RETURN = 0x0d;
+      const int BACKSLASH = 0x5c;
+      const int DOUBLE_QUOTE = 0x22;
+      const int DIGIT_ZERO = 0x30;
+      const int LOWERCASE_A = 0x61;
+      const int MAX_CONTROL = 0x1f;
+      for (int i = 0; i < string.length; i++) {
+        int codeUnit = string.codeUnitAt(i);
+        if (codeUnit <= MAX_CONTROL) {
+          if (codeUnit == NEWLINE) {
+            buffer.write(r"\n");
+          } else if (codeUnit == CARRIGE_RETURN) {
+            buffer.write(r"\r");
+          } else if (codeUnit == TAB) {
+            buffer.write(r"\t");
+          } else {
+            buffer.write(r"\x");
+            // Convert code in range 0x00 .. 0x1f to hex a two-digit hex string.
+            if (codeUnit < 0x10) {
+              buffer.write("0");
+            } else {
+              buffer.write("1");
+              codeUnit -= 0x10;
+            }
+            // Single digit to hex.
+            buffer.writeCharCode(codeUnit < 10 ? DIGIT_ZERO + codeUnit

[Søren Gjesse, 2013/08/16 11:24:57]

Align : with ?

+                                           : LOWERCASE_A - 10 + codeUnit);
+          }
+        } else if (codeUnit == BACKSLASH) {
+          buffer.write(r"\\");
+        } else if (codeUnit == DOUBLE_QUOTE) {

[Søren Gjesse, 2013/08/16 11:24:57]

Why is it that we want to escape double quote?

[Lasse Reichstein Nielsen, 2013/08/16 11:27:41]

Readability - you can read the string and see where it ends, without confusing:
  "argle bargle", "glop glyph"
with two strings.

+          buffer.write(r'\"');
+        } else {
+          buffer.writeCharCode(codeUnit);
+        }
+      }
+      buffer.write('"');
+      return buffer.toString();
     }
     return _objectToString(object);
   }