Make static member functions, added with `def_static`, `staticmethod` descriptor instances (#1732)

include/pybind11/pybind11.h

@@ -1121,7 +1121,7 @@ public:
                 "def_static(...) called with a non-static member function pointer");
         cpp_function cf(std::forward<Func>(f), name(name_), scope(*this),
                         sibling(getattr(*this, name_, none())), extra...);
-        attr(cf.name()) = cf;
+        attr(cf.name()) = staticmethod(cf);
         return *this;
     }
 

include/pybind11/pytypes.h

@@ -742,6 +742,8 @@ inline bool PyEllipsis_Check(PyObject *o) { return o == Py_Ellipsis; }
 
 inline bool PyUnicode_Check_Permissive(PyObject *o) { return PyUnicode_Check(o) || PYBIND11_BYTES_CHECK(o); }
 
+inline bool PyStaticMethod_Check(PyObject *o) { return o->ob_type == &PyStaticMethod_Type; }
+
 class kwargs_proxy : public handle {
 public:
     explicit kwargs_proxy(handle h) : handle(h) { }
@@ -1281,6 +1283,11 @@ public:
     bool is_cpp_function() const { return (bool) cpp_function(); }
 };
 
+class staticmethod : public object {
+public:
+    PYBIND11_OBJECT_CVT(staticmethod, object, detail::PyStaticMethod_Check, PyStaticMethod_New)
+};
+
 class buffer : public object {
 public:
     PYBIND11_OBJECT_DEFAULT(buffer, object, PyObject_CheckBuffer)