Skipping news as this is a fix for a yet unreleased regression.

cc @code-of-kpp

Yep, there's a bug for sure, I had an intuition that if one would come up with some interesting way to cast things, we can break things, just couldn't come up with an example back then.

I definitely got something weird, that I can't quickly figure out:

    def test_pointer_set_contents(self):
        class Struct(Structure):
            _fields_ = [('a', c_int16)]
        p = pointer(Struct(a=23))
        self.assertIs(p._type_, Struct)
        self.assertEqual(cast(p, POINTER(c_int16)).contents._type_, 'h')

        pp = pointer(p)
        self.assertIs(pp._type_, POINTER(Struct))

        cast(pp, POINTER(POINTER(c_int16))).contents.contents = c_int16(32)

        self.assertIs(p.contents, pp.contents.contents)

        self.assertEqual(cast(p, POINTER(c_int16)).contents.value, 32)
        self.assertEqual(p[0].a, 32)  # works
        self.assertEqual(pp[0].contents.a, 32)  # works
        self.assertEqual(pp.contents[0].a, 32)  # works

        self.assertEqual(pp.contents.contents.a, 32)  # fails, wat, holds 23
        self.assertEqual(p.contents.a, 32)  # fails, wat, holds 23

I can't repro your result. For me pp.contents.contents itself leads to the assertion failure in Pointer_get_contents. I'm looking into further.

Very interesting. If you're OK with this, I can spend some time this week investigating too.

Sure. We might need to back out your original fix out of 3.11 until those rough edges are addressed as the next release is going to likely go out either today or tomorrow.

I have a partial solution:

            ptr2ptr = (CDataObject*) PyDict_GetItemString(keep, "1");
            if (ptr2ptr ==  NULL) {
                PyErr_SetString(PyExc_ValueError,
                "Unexpected NULL pointer in _objects");
                return NULL;
            }

            // if we need to return a pointer, an array or a structure,
            // Pointer_item will do the right thing
            if (
                PyCStructTypeObject_Check(stgdict->proto) || 
                PyCArrayTypeObject_Check(stgdict->proto) ||
                PyCPointerTypeObject_Check(stgdict->proto)
            ) {
                return Pointer_item(self, 0);
            } else if ( PyUnicode_Check(stgdict->proto)
                && (strchr("sPzUZXO", PyUnicode_AsUTF8(stgdict->proto)[0]))) {
                // simple pointer types, c_void_p, c_wchar_p, BSTR, ... */
                return Pointer_item(self, 0);
            }

So, basically, if we are about to return Pointer, Structure or an Array, back off to the same thing as [0] will do.

It messes up a bit the garbage collection: replaced values are gonna be saved longer than needed. Still, I think it's a better solution, than what we have now in 3.11, where a memory leak can happen.
All other tests pass.
What do you think?