Use ImagingCore.ptr instead of ImagingCore.id

[homm]

Partially suppress #8340

The non-primary extensions in Pillow don't have direct access to Python's _imaging types, such as Imaging_Type and ImagingObject. However, they often still need to interact with objects passed from Python code. Currently, the raw memory pointer to an Imaging object (ImageCore.id) is passed as an integer and then cast to a memory pointer:

static PyObject *
cms_transform_apply(CmsTransformObject *self, PyObject *args) {
    Py_ssize_t idIn, idOut;
    Imaging im, imOut;

    if (!PyArg_ParseTuple(args, "nn:apply", &idIn, &idOut)) {
        return NULL;
    }

    im = (Imaging)idIn;
    imOut = (Imaging)idOut;

    return Py_BuildValue("i", pyCMSdoTransform(im, imOut, self->transform));
}

It's not safe and can lead to segmentation faults. Python has Capsule objects, which provide a safer way to pass pointers to C code. These are exposed through ImageCore.ptr.

This PR deprecates the raw pointer properties ImageCore.id and ImageCore.unsafe_ptrs, and migrates non-primary extensions to interact with Capsule objects.

[homm]

@python-pillow/pillow-team I need help here)

Could anyone debug pypy3.10 on windows? I can't get what's wrong, since as I can see, the capsule object is correctly restored from the pointer and the capsule object itself is alive.

https://github.com/python-pillow/Pillow/actions/runs/10664609198/job/29556218383?pr=8341#step:27:3342

[homm]

Get it! In pypy repr(capsule) holds the capsuled pointer itself, not the pointer to the PyObject. And even hex(id(capsule)) is not the pointer to PyObject. Lucky, we can reliably distinguish pypy capsule from cpython capsule by absence of trailing "<>".

https://github.com/pypy/pypy/blob/branches/py3.10/pypy/objspace/std/capsuleobject.py#L39

[radarhere]

So is the motivation here just to simplify the code?

Also, we don't necessarily need the deprecations - #4532 (comment)

Pillow makes a commitment to stable public interfaces, which are defined at the Python layer. The C interfaces are explicitly internal, and no effort is made to keep them stable even between minor releases, and no support or warning is given when they change. (IIRC, there are/were people using the internal interfaces, but they've always been explicitly on their own with that)

[homm]

So is the motivation here just to simplify the code?

Added description to PR.

Also, we don't necessarily need the deprecations

While ImageCore is internal Pillow object, it's still Python API. I believe ImageCore.id could be used by third-party extensions (Github search) and can't be removed in a one day.

[radarhere]

Suggested change

	imOut = Image.new(self.output_mode, im.size, None)
	im.load()
	imOut = Image.new(self.output_mode, im.size, None)

This call can still make a difference - it is possible for the size of an image to change after it loads.

from PIL import Image
im = Image.open("Tests/images/g4_orientation_5.tif")
print(im.size)  # (88, 590)
im.load()
print(im.size)  # (590, 88)

[homm]

it is possible for the size of an image to change after it loads

I'm considering this as bug and have patched it in our production brunch: uploadcare@1d77bfe
Do you want I made a PR for this?

[radarhere]

A separate PR would be good, rather than including it here, yeah, thanks.

[homm]

Here it is: #8387