[3.11] gh-108851: Fix support.get_recursion_available() for USE_STACKCHECK (#110127)

Add _testcapi.USE_STACKCHECK.

USE_STACKCHECK on using on Windows 32-bit.

Lib/test/support/__init__.py

@@ -2243,7 +2243,16 @@ def get_recursion_available():
     """
     limit = sys.getrecursionlimit()
     depth = get_recursion_depth()
-    return limit - depth
+
+    try:
+        from _testcapi import USE_STACKCHECK
+    except ImportError:
+        USE_STACKCHECK = False
+
+    if USE_STACKCHECK:
+        return max(limit - depth - 1, 0)
+    else:
+        return limit - depth
 
 @contextlib.contextmanager
 def set_recursion_limit(limit):

Lib/test/test_support.py

@@ -704,6 +704,10 @@ def test_get_recursion_depth(self):
         code = textwrap.dedent("""
             from test import support
             import sys
+            try:
+                from _testcapi import USE_STACKCHECK
+            except ImportError:
+                USE_STACKCHECK = False
 
             def check(cond):
                 if not cond:
@@ -728,19 +732,24 @@ def test_recursive(depth, limit):
                 check(get_depth == depth)
                 test_recursive(depth + 1, limit)
 
+            if USE_STACKCHECK:
+                # f-string consumes 2 frames and -1 for USE_STACKCHECK
+                IGNORE = 3
+            else:
+                # f-string consumes 2 frames
+                IGNORE = 2
+
             # depth up to 25
             with support.infinite_recursion(max_depth=25):
                 limit = sys.getrecursionlimit()
                 print(f"test with sys.getrecursionlimit()={limit}")
-                # Use limit-2 since f-string seems to consume 2 frames.
-                test_recursive(2, limit - 2)
+                test_recursive(2, limit - IGNORE)
 
             # depth up to 500
             with support.infinite_recursion(max_depth=500):
                 limit = sys.getrecursionlimit()
                 print(f"test with sys.getrecursionlimit()={limit}")
-                # limit-2 since f-string seems to consume 2 frames
-                test_recursive(2, limit - 2)
+                test_recursive(2, limit - IGNORE)
         """)
         script_helper.assert_python_ok("-c", code)
 

Modules/_testcapimodule.c

@@ -8203,8 +8203,14 @@ PyInit__testcapi(void)
 #else
     v = Py_False;
 #endif
-    Py_INCREF(v);
-    PyModule_AddObject(m, "WITH_PYMALLOC", v);
+    PyModule_AddObject(m, "WITH_PYMALLOC", Py_NewRef(v));
+
+#ifdef USE_STACKCHECK
+    v = Py_True;
+#else
+    v = Py_False;
+#endif
+    PyModule_AddObject(m, "USE_STACKCHECK", Py_NewRef(v));
 
     TestError = PyErr_NewException("_testcapi.error", NULL, NULL);
     Py_INCREF(TestError);