Fix bug in parsing hex char escapes

It was returning an int not a string. This commit also adds
some test cases I used to find the problem.

tests/test_parsing/test_parsing.py

@@ -138,6 +138,29 @@ def test__parse_literal_string(self):
         self.assertEqual(3, len(outbuf), f"len(outbuf): {len(outbuf)} != 3")
         self.assertListEqual([2, ord("你"), ord("你")], outbuf)
 
+        escaped_char_src = '"\\n"'
+        outbuf = []
+
+        remaining_src = _parse_rhs_literal_string(escaped_char_src, outbuf)
+        self.assertEqual(3, len(outbuf), f"len(outbuf): {len(outbuf)} != 3")
+        self.assertListEqual([2, ord("\n"), ord("\n")], outbuf)
+
+        escaped_backslash_src = '"\\\\"'
+        outbuf = []
+
+        remaining_src = _parse_rhs_literal_string(escaped_backslash_src, outbuf)
+        self.assertEqual(3, len(outbuf), f"len(outbuf): {len(outbuf)} != 3")
+        self.assertListEqual([2, ord("\\"), ord("\\")], outbuf)
+        self.assertEqual("", remaining_src, f"remaining_src: {remaining_src} != ''")
+
+        escaped_backslash_src = '"\\x5C"'
+        outbuf = []
+
+        remaining_src = _parse_rhs_literal_string(escaped_backslash_src, outbuf)
+        self.assertEqual(3, len(outbuf), f"len(outbuf): {len(outbuf)} != 3")
+        self.assertListEqual([2, ord("\\"), ord("\\")], outbuf)
+        self.assertEqual("", remaining_src, f"remaining_src: {remaining_src} != ''")
+
     def test_null(self):
         src = "root ::= "
         rhs_src = ""
@@ -296,6 +319,15 @@ def test_parse_rhs(self):
         )
         logging.debug(f"state.grammar_encoding of {rhs_src}: {state.grammar_encoding}")
 
+        src = 'root ::= "\\\\"'
+        rhs_src = '"\\\\"'
+        state = ParseState()
+        state.symbol_table["root"] = 9
+        _ = parse_rhs(
+            state=state, rhs=rhs_src, rule_name="root", rule_id=9, is_nested=False
+        )
+        logging.debug(f"state.grammar_encoding of {rhs_src}: {state.grammar_encoding}")
+
     def test__parse_symbol_reference(self):
         state = ParseState()
         outbuf = []

transformers_cfg/parser.py

@@ -127,7 +127,7 @@ def parse_char(src) -> (str, str):
             if first > -1:
                 second = hex_to_int(src[3])
                 if second > -1:
-                    return (first << 4) + second, src[4:]
+                    return chr((first << 4) + second), src[4:]
             raise RuntimeError("expecting \\xNN at " + src)
         elif esc in ('"', "[", "]"):
             return esc, src[2:]