From 25a6fbbe88fb21d7ca696b85c7aaec1c6f63dd9c Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Wed, 19 Oct 2022 17:51:09 +0300
Subject: [PATCH] gh-94808: cover `PyFunction_GetDefaults` and
 `PyFunction_SetDefaults`

---
 Lib/test/test_capi.py     | 42 +++++++++++++++++++++++++++++++++++++++
 Modules/_testcapimodule.c | 29 +++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index a2183cfb0fdf6a..68d81a53600b49 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -930,6 +930,48 @@ def some():
         with self.assertRaises(SystemError):
             _testcapi.function_get_module(None)  # not a function
 
+    def test_function_get_defaults(self):
+        def some(pos_only='p', zero=0, optional=None):
+            pass
+
+        defaults = _testcapi.function_get_defaults(some)
+        self.assertEqual(defaults, ('p', 0, None))
+        self.assertEqual(defaults, some.__defaults__)
+
+        with self.assertRaises(SystemError):
+            _testcapi.function_get_module(None)  # not a function
+
+    def test_function_set_defaults(self):
+        def some(pos_only='p', zero=0, optional=None):
+            pass
+
+        old_defaults = ('p', 0, None)
+        self.assertEqual(_testcapi.function_get_defaults(some), old_defaults)
+        self.assertEqual(some.__defaults__, old_defaults)
+
+        with self.assertRaises(SystemError):
+            _testcapi.function_set_defaults(some, 1)  # not tuple or None
+        self.assertEqual(_testcapi.function_get_defaults(some), old_defaults)
+        self.assertEqual(some.__defaults__, old_defaults)
+
+        new_defaults = ('q', 1, None)
+        _testcapi.function_set_defaults(some, new_defaults)
+        self.assertEqual(_testcapi.function_get_defaults(some), new_defaults)
+        self.assertEqual(some.__defaults__, new_defaults)
+
+        class tuplesub(tuple): ...  # tuple subclasses must work
+
+        new_defaults = tuplesub(((1, 2), ['a', 'b'], None))
+        _testcapi.function_set_defaults(some, new_defaults)
+        self.assertEqual(_testcapi.function_get_defaults(some), new_defaults)
+        self.assertEqual(some.__defaults__, new_defaults)
+
+        # `None` is special, it sets `defaults` to `NULL`,
+        # it needs special handling in `_testcapi`:
+        _testcapi.function_set_defaults(some, None)
+        self.assertEqual(_testcapi.function_get_defaults(some), None)
+        self.assertEqual(some.__defaults__, None)
+
 
 class TestPendingCalls(unittest.TestCase):
 
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 624e878b20d822..a42835d97c2c0d 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -5694,6 +5694,33 @@ function_get_module(PyObject *self, PyObject *func)
     }
 }
 
+static PyObject *
+function_get_defaults(PyObject *self, PyObject *func)
+{
+    PyObject *defaults = PyFunction_GetDefaults(func);
+    if (defaults != NULL) {
+        Py_INCREF(defaults);
+        return defaults;
+    } else if (PyErr_Occurred()) {
+        return NULL;
+    } else {
+        Py_RETURN_NONE;  // This can happen when `defaults` are set to `None`
+    }
+}
+
+static PyObject *
+function_set_defaults(PyObject *self, PyObject *args)
+{
+    PyObject *func = NULL, *defaults = NULL;
+    if (!PyArg_ParseTuple(args, "OO", &func, &defaults)) {
+        return NULL;
+    }
+    int result = PyFunction_SetDefaults(func, defaults);
+    if (result == -1)
+        return NULL;
+    Py_RETURN_NONE;
+}
+
 
 static PyObject *test_buildvalue_issue38913(PyObject *, PyObject *);
 static PyObject *getargs_s_hash_int(PyObject *, PyObject *, PyObject*);
@@ -5981,6 +6008,8 @@ static PyMethodDef TestMethods[] = {
     {"function_get_code", function_get_code, METH_O, NULL},
     {"function_get_globals", function_get_globals, METH_O, NULL},
     {"function_get_module", function_get_module, METH_O, NULL},
+    {"function_get_defaults", function_get_defaults, METH_O, NULL},
+    {"function_set_defaults", function_set_defaults, METH_VARARGS, NULL},
     {NULL, NULL} /* sentinel */
 };