[3.12] gh-110782: Fix crash when TypeVar is constructed with keyword args (GH-110784) (#110787)

gh-110782: Fix crash when TypeVar is constructed with keyword args (GH-110784)
(cherry picked from commit d2a536b)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Author: miss-islington

Lib/test/test_typing.py

@@ -554,6 +554,12 @@ def test_many_weakrefs(self):
                     vals[x] = cls(str(x))
                 del vals
 
+    def test_constructor(self):
+        T = TypeVar(name="T")
+        self.assertEqual(T.__name__, "T")
+        self.assertEqual(T.__constraints__, ())
+        self.assertIs(T.__bound__, None)
+
 
 def template_replace(templates: list[str], replacements: dict[str, list[str]]) -> list[tuple[str]]:
     """Renders templates with possible combinations of replacements.

Misc/NEWS.d/next/Core and Builtins/2023-10-12-15-03-24.gh-issue-110782.EqzIzi.rst

@@ -0,0 +1,2 @@
+Fix crash when :class:`typing.TypeVar` is constructed with a keyword
+argument. Patch by Jelle Zijlstra.

Objects/typevarobject.c

@@ -364,24 +364,26 @@ typevar_new_impl(PyTypeObject *type, PyObject *name, PyObject *constraints,
         }
     }
 
-    if (!PyTuple_CheckExact(constraints)) {
-        PyErr_SetString(PyExc_TypeError,
-                        "constraints must be a tuple");
-        return NULL;
-    }
-    Py_ssize_t n_constraints = PyTuple_GET_SIZE(constraints);
-    if (n_constraints == 1) {
-        PyErr_SetString(PyExc_TypeError,
-                        "A single constraint is not allowed");
-        Py_XDECREF(bound);
-        return NULL;
-    } else if (n_constraints == 0) {
-        constraints = NULL;
-    } else if (bound != NULL) {
-        PyErr_SetString(PyExc_TypeError,
-                        "Constraints cannot be combined with bound=...");
-        Py_XDECREF(bound);
-        return NULL;
+    if (constraints != NULL) {
+        if (!PyTuple_CheckExact(constraints)) {
+            PyErr_SetString(PyExc_TypeError,
+                            "constraints must be a tuple");
+            return NULL;
+        }
+        Py_ssize_t n_constraints = PyTuple_GET_SIZE(constraints);
+        if (n_constraints == 1) {
+            PyErr_SetString(PyExc_TypeError,
+                            "A single constraint is not allowed");
+            Py_XDECREF(bound);
+            return NULL;
+        } else if (n_constraints == 0) {
+            constraints = NULL;
+        } else if (bound != NULL) {
+            PyErr_SetString(PyExc_TypeError,
+                            "Constraints cannot be combined with bound=...");
+            Py_XDECREF(bound);
+            return NULL;
+        }
     }
     PyObject *module = caller();
     if (module == NULL) {