gh-94808: add tests covering PyFunction_{Get,Set}Closure

Lib/test/test_capi/test_misc.py

@@ -1171,6 +1171,124 @@ class dictsub(dict): ...  # dict subclasses must work
         self.assertEqual(_testcapi.function_get_kw_defaults(some), None)
         self.assertEqual(some.__kwdefaults__, None)
 
+    def test_function_get_closure(self):
+        from types import CellType
+
+        def regular_function(): ...
+        def unused_one_level(arg1):
+            def inner(arg2, arg3): ...
+            return inner
+        def unused_two_levels(arg1, arg2):
+            def decorator(arg3, arg4):
+                def inner(arg5, arg6): ...
+                return inner
+            return decorator
+        def with_one_level(arg1):
+            def inner(arg2, arg3):
+                return arg1 + arg2 + arg3
+            return inner
+        def with_two_levels(arg1, arg2):
+            def decorator(arg3, arg4):
+                def inner(arg5, arg6):
+                    return arg1 + arg2 + arg3 + arg4 + arg5 + arg6
+                return inner
+            return decorator
+
+        # Functions without closures:
+        self.assertIsNone(_testcapi.function_get_closure(regular_function))
+        self.assertIsNone(regular_function.__closure__)
+
+        func = unused_one_level(1)
+        closure = _testcapi.function_get_closure(func)
+        self.assertIsNone(closure)
+        self.assertIsNone(func.__closure__)
+
+        func = unused_two_levels(1, 2)(3, 4)
+        closure = _testcapi.function_get_closure(func)
+        self.assertIsNone(closure)
+        self.assertIsNone(func.__closure__)
+
+        # Functions with closures:
+        func = with_one_level(5)
+        closure = _testcapi.function_get_closure(func)
+        self.assertEqual(closure, func.__closure__)
+        self.assertIsInstance(closure, tuple)
+        self.assertEqual(len(closure), 1)
+        self.assertEqual(len(closure), len(func.__code__.co_freevars))
+        self.assertTrue(all(isinstance(cell, CellType) for cell in closure))
+        self.assertTrue(closure[0].cell_contents, 5)
+
+        func = with_two_levels(1, 2)(3, 4)
+        closure = _testcapi.function_get_closure(func)
+        self.assertEqual(closure, func.__closure__)
+        self.assertIsInstance(closure, tuple)
+        self.assertEqual(len(closure), 4)
+        self.assertEqual(len(closure), len(func.__code__.co_freevars))
+        self.assertTrue(all(isinstance(cell, CellType) for cell in closure))
+        self.assertEqual([cell.cell_contents for cell in closure],
+                         [1, 2, 3, 4])
+
+    def test_function_get_closure_error(self):
+        with self.assertRaises(SystemError):
+            _testcapi.function_get_closure(1)
+        with self.assertRaises(SystemError):
+            _testcapi.function_get_closure(None)
+
+    def test_function_set_closure(self):
+        from types import CellType
+
+        def function_without_closure(): ...
+        def function_with_closure(arg):
+            def inner():
+                return arg
+            return inner
+
+        func = function_without_closure
+        _testcapi.function_set_closure(func, (CellType(1), CellType(1)))
+        closure = _testcapi.function_get_closure(func)
+        self.assertEqual([c.cell_contents for c in closure], [1, 1])
+        self.assertEqual([c.cell_contents for c in func.__closure__], [1, 1])
+
+        func = function_with_closure(1)
+        _testcapi.function_set_closure(func,
+                                       (CellType(1), CellType(2), CellType(3)))
+        closure = _testcapi.function_get_closure(func)
+        self.assertEqual([c.cell_contents for c in closure], [1, 2, 3])
+        self.assertEqual([c.cell_contents for c in func.__closure__], [1, 2, 3])
+
+    def test_function_set_closure_none(self):
+        def function_without_closure(): ...
+        def function_with_closure(arg):
+            def inner():
+                return arg
+            return inner
+
+        _testcapi.function_set_closure(function_without_closure, None)
+        self.assertIsNone(
+            _testcapi.function_get_closure(function_without_closure))
+        self.assertIsNone(function_without_closure.__closure__)
+
+        _testcapi.function_set_closure(function_with_closure, None)
+        self.assertIsNone(
+            _testcapi.function_get_closure(function_with_closure))
+        self.assertIsNone(function_with_closure.__closure__)
+
+    def test_function_set_closure_errors(self):
+        def function_without_closure(): ...
+
+        with self.assertRaises(SystemError):
+            _testcapi.function_set_closure(None, ())  # not a function
+
+        with self.assertRaises(SystemError):
+            _testcapi.function_set_closure(function_without_closure, 1)
+        self.assertIsNone(function_without_closure.__closure__)  # no change
+
+        # NOTE: this works, but goes against the docs:
+        _testcapi.function_set_closure(function_without_closure, (1, 2))
+        self.assertEqual(
+            _testcapi.function_get_closure(function_without_closure), (1, 2))
+        self.assertEqual(function_without_closure.__closure__, (1, 2))
+
 
 class TestPendingCalls(unittest.TestCase):
 

Modules/_testcapimodule.c

@@ -6009,6 +6009,33 @@ function_set_kw_defaults(PyObject *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
+static PyObject *
+function_get_closure(PyObject *self, PyObject *func)
+{
+    PyObject *closure = PyFunction_GetClosure(func);
+    if (closure != NULL) {
+        Py_INCREF(closure);
+        return closure;
+    } else if (PyErr_Occurred()) {
+        return NULL;
+    } else {
+        Py_RETURN_NONE;  // This can happen when `closure` is set to `None`
+    }
+}
+
+static PyObject *
+function_set_closure(PyObject *self, PyObject *args)
+{
+    PyObject *func = NULL, *closure = NULL;
+    if (!PyArg_ParseTuple(args, "OO", &func, &closure)) {
+        return NULL;
+    }
+    int result = PyFunction_SetClosure(func, closure);
+    if (result == -1)
+        return NULL;
+    Py_RETURN_NONE;
+}
+
 
 // type watchers
 
@@ -6434,6 +6461,8 @@ static PyMethodDef TestMethods[] = {
     {"function_set_defaults", function_set_defaults, METH_VARARGS, NULL},
     {"function_get_kw_defaults", function_get_kw_defaults, METH_O, NULL},
     {"function_set_kw_defaults", function_set_kw_defaults, METH_VARARGS, NULL},
+    {"function_get_closure", function_get_closure, METH_O, NULL},
+    {"function_set_closure", function_set_closure, METH_VARARGS, NULL},
     {"add_type_watcher", add_type_watcher, METH_O, NULL},
     {"clear_type_watcher", clear_type_watcher, METH_O, NULL},
     {"watch_type", watch_type, METH_VARARGS, NULL},