gh-96848: Fix -X int_max_str_digits option parsing (#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

Lib/test/test_cmd_line.py

@@ -871,6 +871,8 @@ def test_int_max_str_digits(self):
         assert_python_failure('-X', 'int_max_str_digits', '-c', code)
         assert_python_failure('-X', 'int_max_str_digits=foo', '-c', code)
         assert_python_failure('-X', 'int_max_str_digits=100', '-c', code)
+        assert_python_failure('-X', 'int_max_str_digits', '-c', code,
+                              PYTHONINTMAXSTRDIGITS='4000')
 
         assert_python_failure('-c', code, PYTHONINTMAXSTRDIGITS='foo')
         assert_python_failure('-c', code, PYTHONINTMAXSTRDIGITS='100')

Misc/NEWS.d/next/Core and Builtins/2022-09-21-14-38-31.gh-issue-96848.WuoLzU.rst

+Fix command line parsing: reject :option:`-X int_max_str_digits <-X>` option
+with no value (invalid) when the :envvar:`PYTHONINTMAXSTRDIGITS` environment
+variable is set to a valid limit. Patch by Victor Stinner.

Python/initconfig.c

@@ -1779,10 +1779,10 @@ static PyStatus
 config_init_int_max_str_digits(PyConfig *config)
 {
     int maxdigits;
-    int valid = 0;
 
     const char *env = config_get_env(config, "PYTHONINTMAXSTRDIGITS");
     if (env) {
+        int valid = 0;
         if (!_Py_str_to_int(env, &maxdigits)) {
             valid = ((maxdigits == 0) || (maxdigits >= _PY_LONG_MAX_STR_DIGITS_THRESHOLD));
         }
@@ -1800,6 +1800,7 @@ config_init_int_max_str_digits(PyConfig *config)
     const wchar_t *xoption = config_get_xoption(config, L"int_max_str_digits");
     if (xoption) {
         const wchar_t *sep = wcschr(xoption, L'=');
+        int valid = 0;
         if (sep) {
             if (!config_wstr_to_int(sep + 1, &maxdigits)) {
                 valid = ((maxdigits == 0) || (maxdigits >= _PY_LONG_MAX_STR_DIGITS_THRESHOLD));