Dynamically modifiy requirements through plugin

[staley-arlut]

What is the correct way to have a setuptools distutils.commands plugin dynamically add requirements and optional requirements?

I have a hack of a solution that involves manipulating the install_requires and extras_require attributes on the distribution/distribution.metadata objects during my custom command's finalize_options step. This seems to work as far back as setuptools v39.2.0, but has recently stopped working as of v75.2.0.

For context, my use case is due to Google Protocol Buffers(protobuf):

The plugin command runs the protobuf compiler (protoc) at build time in order to generate python source modules. Unfortunately, using protobuf makes packaging python wheels difficult due to needing to match the runtime package protobuf version with the version of the protobuf compiler (protoc) used at build time.

I try to keep my source code compatible with as wide a range of versions as I can. For instance, I've written package code that can work with protobuf versions 3.5 through 5.x. However when protoc generates it's python modules, it inherently reduces the versions of the protobuf package my wheel is compatible with. It even seems like for now (pre-2025), the protobuf developers want you to match the versions of the generator and runtime library exactly (see (cross-version-runtime-guarantee)[https://protobuf.dev/support/cross-version-runtime-guarantee]).

So, my solution to this has been to have my setuptools plugin dynamically lock the version requirement of the protobuf runtime package based on the version of protoc it used to generate the wheel. I don't love this solution, because it means you cannot install two wheels that were built with different protoc versions to the same environment, but I'm not sure how else to solve this problem.