gh-96512: Move int_max_str_digits setting to PyConfig (#96944)

It had to live as a global outside of PyConfig for stable ABI reasons in
the pre-3.12 backports.

This removes the `_Py_global_config_int_max_str_digits` and gets rid of
the equivalent field in the internal `struct _is PyInterpreterState` as
code can just use the existing nested config struct within that.

Adds tests to verify unique settings and configs in subinterpreters.

Lib/test/test_capi.py

@@ -999,6 +999,39 @@ class SubinterpreterTest(unittest.TestCase):
             self.assertEqual(ret, 0)
             self.assertEqual(pickle.load(f), {'a': '123x', 'b': '123'})
 
+    def test_py_config_isoloated_per_interpreter(self):
+        # A config change in one interpreter must not leak to out to others.
+        #
+        # This test could verify ANY config value, it just happens to have been
+        # written around the time of int_max_str_digits. Refactoring is okay.
+        code = """if 1:
+        import sys, _testinternalcapi
+
+        # Any config value would do, this happens to be the one being
+        # double checked at the time this test was written.
+        config = _testinternalcapi.get_config()
+        config['int_max_str_digits'] = 55555
+        _testinternalcapi.set_config(config)
+        sub_value = _testinternalcapi.get_config()['int_max_str_digits']
+        assert sub_value == 55555, sub_value
+        """
+        before_config = _testinternalcapi.get_config()
+        assert before_config['int_max_str_digits'] != 55555
+        self.assertEqual(support.run_in_subinterp(code), 0,
+                         'subinterp code failure, check stderr.')
+        after_config = _testinternalcapi.get_config()
+        self.assertIsNot(
+                before_config, after_config,
+                "Expected get_config() to return a new dict on each call")
+        self.assertEqual(before_config, after_config,
+                         "CAUTION: Tests executed after this may be "
+                         "running under an altered config.")
+        # try:...finally: calling set_config(before_config) not done
+        # as that results in sys.argv, sys.path, and sys.warnoptions
+        # "being modified by test_capi" per test.regrtest.  So if this
+        # test fails, assume that the environment in this process may
+        # be altered and suspect.
+
     def test_mutate_exception(self):
         """
         Exceptions saved in global module state get shared between

Lib/test/test_cmd_line.py

@@ -882,7 +882,8 @@ class CmdLineTest(unittest.TestCase):
             return tuple(int(i) for i in out.split())
 
         res = assert_python_ok('-c', code)
-        self.assertEqual(res2int(res), (-1, sys.get_int_max_str_digits()))
+        current_max = sys.get_int_max_str_digits()
+        self.assertEqual(res2int(res), (current_max, current_max))
         res = assert_python_ok('-X', 'int_max_str_digits=0', '-c', code)
         self.assertEqual(res2int(res), (0, 0))
         res = assert_python_ok('-X', 'int_max_str_digits=4000', '-c', code)

Lib/test/test_embed.py

@@ -434,6 +434,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         'install_signal_handlers': 1,
         'use_hash_seed': 0,
         'hash_seed': 0,
+        'int_max_str_digits': sys.int_info.default_max_str_digits,
         'faulthandler': 0,
         'tracemalloc': 0,
         'perf_profiling': 0,
@@ -876,6 +877,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'platlibdir': 'my_platlibdir',
             'module_search_paths': self.IGNORE_CONFIG,
             'safe_path': 1,
+            'int_max_str_digits': 31337,
 
             'check_hash_pycs_mode': 'always',
             'pathconfig_warnings': 0,
@@ -912,6 +914,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'platlibdir': 'env_platlibdir',
             'module_search_paths': self.IGNORE_CONFIG,
             'safe_path': 1,
+            'int_max_str_digits': 4567,
         }
         self.check_all_configs("test_init_compat_env", config, preconfig,
                                api=API_COMPAT)
@@ -944,6 +947,7 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'platlibdir': 'env_platlibdir',
             'module_search_paths': self.IGNORE_CONFIG,
             'safe_path': 1,
+            'int_max_str_digits': 4567,
         }
         self.check_all_configs("test_init_python_env", config, preconfig,
                                api=API_PYTHON)

Lib/test/test_int.py

@@ -770,6 +770,26 @@ class IntStrDigitLimitsTests(unittest.TestCase):
         with self.subTest(base=base):
             self._other_base_helper(base)
 
+    def test_int_max_str_digits_is_per_interpreter(self):
+        # Changing the limit in one interpreter does not change others.
+        code = """if 1:
+        # Subinterpreters maintain and enforce their own limit
+        import sys
+        sys.set_int_max_str_digits(2323)
+        try:
+            int('3'*3333)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError('Expected a int max str digits ValueError.')
+        """
+        with support.adjust_int_max_str_digits(4000):
+            before_value = sys.get_int_max_str_digits()
+            self.assertEqual(support.run_in_subinterp(code), 0,
+                             'subinterp code failure, check stderr.')
+            after_value = sys.get_int_max_str_digits()
+            self.assertEqual(before_value, after_value)
+
 
 class IntSubclassStrDigitLimitsTests(IntStrDigitLimitsTests):
     int_class = IntSubclass