bpo-44378: Fix a compiler warning in Py_IS_TYPE() (GH-26644)

Py_IS_TYPE() no longer uses Py_TYPE() to avoid a compiler warning:
no longer cast "const PyObject*" to "PyObject*".
(cherry picked from commit 304dfec)

Co-authored-by: Victor Stinner <[email protected]>

Author: miss-islington

Include/object.h

@@ -141,7 +141,9 @@ static inline Py_ssize_t _Py_REFCNT(const PyObject *ob) {
 
 
 static inline int _Py_IS_TYPE(const PyObject *ob, const PyTypeObject *type) {
-    return Py_TYPE(ob) == type;
+    // bpo-44378: Don't use Py_TYPE() since Py_TYPE() requires a non-const
+    // object.
+    return ob->ob_type == type;
 }
 #define Py_IS_TYPE(ob, type) _Py_IS_TYPE(_PyObject_CAST_CONST(ob), type)
 

Misc/NEWS.d/next/C API/2021-06-10-15-22-31.bpo-44378.jGYakF.rst

@@ -0,0 +1,3 @@
+:c:func:`Py_IS_TYPE` no longer uses :c:func:`Py_TYPE` to avoid a compiler
+warning: no longer cast ``const PyObject*`` to ``PyObject*``.
+Patch by Victor Stinner.