Cython deprecation warning: "The 'IF' statement is deprecated"

[jameslamb]

Description

cuML distributes both GPU-accelerated and CPU-only packages.

At build time, it controls whether GPU-related bits of the Cython code are built by passing GPUBUILD through to Cython.

cuml/python/cuml/CMakeLists.txt

Lines 153 to 154 in f29293f

	list(APPEND CYTHON_FLAGS
	"--compile-time-env GPUBUILD=0")

That guards imports like this:

cuml/python/cuml/cuml/internals/base.pyx

Lines 74 to 76 in f29293f

	IF GPUBUILD == 1:
	import pylibraft.common.handle
	import cuml.common.cuda

That pattern is deprecated in the version of Cython used in builds for the 25.02 release, resulting in many of this type of warning in CI logs:

[347/584] Transpiling base.pyx to base.cxx
warning: /__w/cuml/cuml/python/cuml/cuml/internals/base.pyx:74:0: The 'IF' statement is deprecated and will be removed in a future Cython version. Consider using runtime conditions or C macros instead. See cython/cython#4310

cuML builds should be adapted to use a different pattern.

Benefits of this work

• allows cuML to be built with newer versions of Cython (assuming Cython eventually removes support for IF)

Acceptance Criteria

• cuML build do not use the deprecated Cython IF pattern for conditional compilation

Approach

See the discussion and links in cython/cython#4310 for ideas on how to approach this.

Notes

I'm opening this to track, but not planning to personally work on it.

[dantegd]

Refactoring our Python code to have the C++ calls separate from the Python layer, which will allow us to stop using the Cython IF has been on our backlog for quite some time now, and hopefully something we can do on of the upcoming versions.