bpo-36817: Do not decrement reference for expr_text on fstring = parsing failure (pythonGH-13256)

Author: pablogsal

Lib/test/test_fstring.py

@@ -1148,6 +1148,8 @@ def __repr__(self):
  self.assertEqual(f'{C()=:x}', 'C()=FORMAT-x')
  self.assertEqual(f'{C()=!r:*^20}', 'C()=********REPR********')
 
+ self.assertRaises(SyntaxError, eval, "f'{C=]'")
+
  def test_walrus(self):
  x = 20
  # This isn't an assignment expression, it's 'x', with a format

Python/ast.c

@@ -5283,7 +5283,6 @@ fstring_find_expr(const char **str, const char *end, int raw, int recurse_lvl,
  /* Falls through to error. */
 
 error:
- Py_XDECREF(expr_text);
  return -1;
 
 }