Add proper escaping for String::escape_to

string/string.mbt

@@ -18,19 +18,38 @@
 /// This method only escapes characters below 0x20 and the following characters:
 /// `"`, `'`, `\`.
 pub fn escape_to(self : String, buf : Buffer) -> Unit {
+  fn write_escaped_ch(ch : Char) -> Unit {
+    buf.write_char('\\')
+    buf.write_char(ch)
+  }
+
+  fn to_hex_digit(i : Int) -> Char {
+    if i < 10 {
+      Char::from_int('0'.to_int() + i)
+    } else {
+      Char::from_int('a'.to_int() + (i - 10))
+    }
+  }
+
   let mut ix = 0
   while ix < self.length() {
     let ch = self[ix]
     match ch {
-      '"' | '\'' | '\\' => {
-        buf.write_char('\\')
-        buf.write_char(ch)
-      }
-      '\n' => {
-        buf.write_char('\\')
-        buf.write_char('n')
-      }
-      _ => buf.write_char(ch)
+      '"' | '\'' | '\\' => write_escaped_ch(ch)
+      '\n' => write_escaped_ch('n')
+      '\r' => write_escaped_ch('r')
+      '\b' => write_escaped_ch('b')
+      '\t' => write_escaped_ch('t')
+      _ =>
+        if ch.to_int() < 0x20 {
+          buf.write_char('\\')
+          buf.write_char('x')
+          let ich = ch.to_int()
+          buf.write_char(to_hex_digit(ich / 16))
+          buf.write_char(to_hex_digit(ich % 16))
+        } else {
+          buf.write_char(ch)
+        }
     }
     ix += 1
   }