[FR] Ability to dynamically specify "build wheel" dependencies

[mgorny]

What's the problem this feature will solve?

Some projects have specific dynamic dependencies for build* commands such as cmake. Currently, such dependencies either have to be specified a. as build-system.requires, or b. via setup_requires. The former method only permits static dependencies, so we can't express "[cmake] only if no system CMake is available", the latter is deprecated — and both of them apply to source distributions, whereas we need it only for wheel builds.

Describe the solution you'd like

I'd like a non-deprecated option to pass wheel building requirements to setup() function, so they'd be returned by the backend's get_requires_for_build_wheel() method.

Alternative Solutions

The alternative is for every such package to use a custom backend based on setuptools', and have the backend override get_requires_for_build_wheel(). However, it seems a bit of an overkill.

Additional context

No response

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