[j8] Fix parse error with ( ) tokens in JSON/JSON8

These are valid in J8 Notation (TYG8), but not JSON or JSON8.

data_lang/j8.py

@@ -562,7 +562,6 @@ class Parser(object):
     def __init__(self, s, is_j8):
         # type: (str, bool) -> None
         self.s = s
-        self.is_j8 = is_j8
         self.lang_str = "J8" if is_j8 else "JSON"
 
         self.lexer = LexerDecoder(s, is_j8)
@@ -713,16 +712,10 @@ def _ParseValue(self):
             raise self._Error('Unexpected EOF while parsing %s' %
                               self.lang_str)
 
-        elif self.tok_id == Id.Unknown_Tok:
+        else:  # Id.Unknown_Tok, Id.J8_{LParen,RParen}
             raise self._Error('Invalid token while parsing %s: %s' %
                               (self.lang_str, Id_str(self.tok_id)))
 
-        else:
-            # This should never happen
-            part = self.s[self.start_pos:self.end_pos]
-            raise AssertionError('Unexpected token %s %r' %
-                                 (Id_str(self.tok_id), part))
-
     def ParseValue(self):
         # type: () -> value_t
         """ Raises error.Decode. """

data_lang/json-errors.sh

@@ -41,6 +41,9 @@ test-parse-errors() {
 
   # Invalid token
   _error-case-X 1 'echo + | json read'
+
+  # TYG8 token, not JSON8 token
+  _error-case-X 1 'echo "(" | json read'
 }
 
 test-lex-errors() {

spec/ysh-json.test.sh

@@ -874,3 +874,14 @@ declare -- y=$'\xbc'
 b'\yf0\y9f\ya4\yff'
 declare -- z=$'\xf0\x9f\xa4\xff'
 ## END
+
+#### TYG8 token in JSON / JSON8
+
+echo "(" | json read
+echo status=$?
+
+echo ")" | json8 read
+echo status=$?
+
+## STDOUT:
+## END