bpo-39947: Move get_recursion_depth() to _testinternalcapi (GH-18974)

Move get_recursion_depth() function from _testcapi to
_testinternalcapi to avoid accessing PyThreadState attributes
directly in _testcapi.

Lib/test/test_exceptions.py

@@ -994,7 +994,7 @@ class ExceptionTests(unittest.TestCase):
         # finalization of these locals.
         code = """if 1:
             import sys
-            from _testcapi import get_recursion_depth
+            from _testinternalcapi import get_recursion_depth
 
             class MyException(Exception): pass
 

Lib/test/test_sys.py

@@ -241,7 +241,7 @@ class SysModuleTest(unittest.TestCase):
         # mark". Otherwise, it may not be possible anymore to
         # reset the overflowed flag to 0.
 
-        from _testcapi import get_recursion_depth
+        from _testinternalcapi import get_recursion_depth
 
         def set_recursion_limit_at_depth(depth, limit):
             recursion_depth = get_recursion_depth()

Modules/_testcapimodule.c

@@ -5,9 +5,11 @@
  * standard Python regression test, via Lib/test/test_capi.py.
  */
 
-/* The Visual Studio projects builds _testcapi with Py_BUILD_CORE_MODULE
-   define, but we only want to test the public C API, not the internal
-   C API. */
+/* This module tests the public (Include/ and Include/cpython/) C API.
+   The internal C API must not be used here: use _testinternalcapi for that.
+
+   The Visual Studio projects builds _testcapi with Py_BUILD_CORE_MODULE
+   macro defined, but only the public C API must be tested here. */
 #undef Py_BUILD_CORE_MODULE
 
 #define PY_SSIZE_T_CLEAN
@@ -4523,15 +4525,6 @@ test_PyTime_AsMicroseconds(PyObject *self, PyObject *args)
     return _PyTime_AsNanosecondsObject(ms);
 }
 
-static PyObject*
-get_recursion_depth(PyObject *self, PyObject *args)
-{
-    PyThreadState *tstate = PyThreadState_Get();
-
-    /* subtract one to ignore the frame of the get_recursion_depth() call */
-    return PyLong_FromLong(tstate->recursion_depth - 1);
-}
-
 static PyObject*
 pymem_buffer_overflow(PyObject *self, PyObject *args)
 {
@@ -5486,7 +5479,6 @@ static PyMethodDef TestMethods[] = {
 #endif
     {"PyTime_AsMilliseconds", test_PyTime_AsMilliseconds, METH_VARARGS},
     {"PyTime_AsMicroseconds", test_PyTime_AsMicroseconds, METH_VARARGS},
-    {"get_recursion_depth", get_recursion_depth, METH_NOARGS},
     {"pymem_buffer_overflow", pymem_buffer_overflow, METH_NOARGS},
     {"pymem_api_misuse", pymem_api_misuse, METH_NOARGS},
     {"pymem_malloc_without_gil", pymem_malloc_without_gil, METH_NOARGS},

Modules/_testinternalcapi.c

@@ -9,7 +9,7 @@
 #define PY_SSIZE_T_CLEAN
 
 #include "Python.h"
-#include "pycore_initconfig.h"
+#include "pycore_initconfig.h"   // _Py_GetConfigsAsDict()
 
 
 static PyObject *
@@ -19,8 +19,19 @@ get_configs(PyObject *self, PyObject *Py_UNUSED(args))
 }
 
 
+static PyObject*
+get_recursion_depth(PyObject *self, PyObject *args)
+{
+    PyThreadState *tstate = PyThreadState_Get();
+
+    /* subtract one to ignore the frame of the get_recursion_depth() call */
+    return PyLong_FromLong(tstate->recursion_depth - 1);
+}
+
+
 static PyMethodDef TestMethods[] = {
     {"get_configs", get_configs, METH_NOARGS},
+    {"get_recursion_depth", get_recursion_depth, METH_NOARGS},
     {NULL, NULL} /* sentinel */
 };