What way to choose to fix `Warning: ULONG_PTR differs in levels of indirection from void *` in AC-generated code?

[arhadthedev]

Currently, Argument Clinic generates initialization of ULONG_PTR arguments using PyLong_AsVoidPtr(). The reason is sizeof(ULONG_PTR) == sizeof(void*) akin to C99 uintptr_t.

However, a compiler warns that implicit conversion of a pointer to a pointer-sized integer is not the best practice. This is relevant for _overlapped.CreateIoCompletionPort():

cpython/Modules/clinic/overlapped.c.h

Lines 15 to 18 in 3e7cad3

	_overlapped_CreateIoCompletionPort_impl(PyObject *module, HANDLE FileHandle,
	HANDLE ExistingCompletionPort,
	ULONG_PTR CompletionKey,
	DWORD NumberOfConcurrentThreads);

cpython/Modules/clinic/overlapped.c.h

Line 40 in 3e7cad3

CompletionKey = PyLong_AsVoidPtr(args[2]);

I see three ways to fix it in ULONG_PTR Argument Clinic converter and need an opinion on how to address the warning best:

• generate in-place cast: CompletionKey = (ULONG_PTR)PyLong_AsVoidPtr(args[2]); or
• add a private Windows-only #define _PyLong_AsUlongPtr(arg) (ULONG_PTR)PyLong_AsVoidPtr(arg) macro so the generated line becomes CompletionKey = PyLong_AsUlongPtr(args[2]); or
• add a public Windows-only PyLong_AsUlongPtr entity and document it so Python integrators and module authors also can work with this volatile WinAPI type

Linked PRs

• gh-95417: Quick fix of ULONG_PTR differs in levels of indirection from void * #95538
• gh-95417: Apply a proper fix for previously fast-fixed ULONG_PTR differs in levels of indirection from void * #95518

[eryksun]

The C API could support cross-platform PyLong_AsUintptr_t() and PyLong_FromUintptr_t(). The type definitions for ULONG_PTR and uintptr_t are compatible in Windows. For 64-bit, they're both unsigned __int64. For 32-bit, uintptr_t is unsigned int, and ULONG_PTR is unsigned long.

[arhadthedev]

To fix the warning, two steps are necessary:

• gh-95417: Add PyLong_FromUintptr_t and PyLong_AsUintptr_t #95446 (deciding first whether PyLong_*Uintptr_t should be a macro/inline function or exported from python3.dll/.so)
• gh-95417: Apply a proper fix for previously fast-fixed ULONG_PTR differs in levels of indirection from void * #95518

[arhadthedev]

According to https://devguide.python.org/developer-workflow/c-api/#guidelines-for-adding-to-the-limited-api, addition of stable ABI requires long discussion. I'm not ready for this for the sake of a single use case so closing this issue.