RFC: Make our `cuda-*` packages depend on the new `cuda-toolkit` metapackage without version constraints?

[leofang]

I am thinking to add a mandatory dependency cuda-toolkit == 13.* to cuda-bindings. This allows using it to control the version, ex:

pip install cuda-bindings cuda-toolkit=13

or

pip install cuda-bindings[all] cuda-toolkit==12.9

similar to cuda-version on conda.

Admittedly, this won't work fully because pip does not allow us to patch repodata and fix all published all packages to enforce this (we did this for all CUDA packages ever published on conda-forge when cuda-version was introduced). But it is still a step forward I'd argue. Thoughts? @kkraus14 @bdice @rwgk @shwina @carterbox

Originally posted by @leofang in #883 (comment)

[leofang]

From @kkraus14:

I think this makes sense, though I would be more supportive if we could introduce a cuda-version metapackage similar to what we have in conda and have the library packages depend on the cuda-version metapackage. This way there's a solution for non-CTK packages as well and would make something like pip install some_non_ctk_package cuda-version=13 a bit more intuitive as well.

The only thing I don't like is something like pip install cuda-bindings[all] cuda-toolkit=13 nvidia-cublas-cu12 would still happily solve because the cublas package doesn't depend on the cuda-toolkit package.

[carterbox]

For clarify. The current state is that we install like so:

cuda-bindings==12.9.*       # without CTK wheels
cuda-bindings[all]==12.9.*  # with CTK wheels

But you propose to move to installing like so:

cuda-bindings==12.9.*              # without CTK wheels
cuda-bindings cudatoolkit==12.9.*  # with CTK wheels

Is that correct?

[kkraus14]

@carterbox, no, if you did pip install cuda-bindings cudatoolkit==12.9.*, it would still be without CTK wheels, but it would solve to the 12.9 compatible cuda-bindings package. To install with CTK wheels you would do pip install cuda-bindings[all] cudatoolkit==12.9.*. Doing cuda-bindings[all]==12.9.* would continue to be supported. The proposal is to use the cudatoolkit metapackage to constrain versioning since it doesn't have anything in of itself outside of optional dependencies.