warn if cuda packages are installed implicitly

[minrk]

closes #426

doesn't change default behavior, but adds a warning if cuda is not requested but 'cudatoolkit' is pulled in, as suggested by @maresb. The presence of 'cudatoolkit' itself in the dependency list is considered sufficient for an 'explicit cuda' signal.

I could leave out that condition because the available version is still implicit, which may trip folks up.

I initially wanted to allow specifying a version with --with-cuda [version], but click doesn't seem to want folks to have options with 0 or 1 args. Plus, virtual package specs already solve this, so it's not worth the fight with click.

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[maresb]

Wow, this is very exciting! Too bad about the Click annoyance. What if we made the CUDA version mandatory?

Now that I have your attention, can I ask a few quick questions about CUDA support, most of which are out-of-scope for this PR?

• Are there other potential CUDA indicators we might want to consider besides cudatoolkit?
• We seem to have this hard-coded default 11.4 version. Should we regularly update, and if so, at what frequency and with which criteria / delay?
• There seems to be a lot of ugly code associated with the default virtual package spec. Do you think it be feasible to instead replace most of this code with the parsing of a default-virtual-packages.yml file?

[minrk]

mandatory version should work fine.

I'm afraid I can't really answer the cuda questions, since I'm not a cuda user. I'm mostly here for making it easier to not use cuda. In my experience, cudatoolkit is ~always present when cuda's depended upon, but I can't say for sure. It's probably a 'good enough' indicator to start with.

Re: the version bump, I think making the version string required makes it easier to leave the default implicit version alone. Then you need to specify the version if you want to avoid the warning or if you want a more recent version. The implicit cuda message can reflect that.

There seems to be a lot of ugly code associated with the default virtual package spec. Do you think it be feasible to instead replace most of this code with the parsing of a default-virtual-packages.yml file?

I'll have a look if I get a chance. Would need #429

[minrk]

flake8 complains about complexity. I don't really know how to respond to that other than suggesting that the complexity check should be removed. I don't think I have the authority to refactor to reduce complexity.

[maresb]

Thanks a lot for this great work! Sorry about the complexity issue. Would it work to add # noqa: C901 to the definition line of make_lock_files?

[minrk]

noqa comment works, thanks

[maresb]

I think this is really good and unlikely to break anything. I'm just going to merge in a few days if there's no further feedback.