How are you supposed to use config_settings_build_wheel correctly?

[henryborchers]

I'm confused by the docs regarding config_settings_build_wheel and the rest of the config_settings_* settings.

From what I can tell, to config_settings_build_wheel can ONLY be used within a build env and ONLY when you set "package=wheel" in [testenv].

When I do that, each environment has it's own package environment. So this means that if I want to change anything in the arguments sent to the pep-517 builder, I have to create a [testenv:.pkg-cpython39], [testenv:.pkg-cpython310],[testenv:.pkg-cpython311], etc... for each environment. Please correct me if I'm wrong.

I see that I can set "wheel_build_env" in [testenv] to ".pkg" and set "config_settings_build_wheel" within [testenv:.pkg]. However, this only works if it's a universal wheel and not helpful if you have C-extensions that need to be built. (Also, I can't figure out how to override that from the command line) Again, please correctly me if I'm wrong here too.

How are you supposed to run ALL your test environments with "--config-setting=some_setting=somevalue" being passed to the PEP-517 backend builder.

Here is my use use case to show you what I want to do.

I have a custom PEP-517 builder that helps me build my C extension and link them to libraries provided by a package manager. What I would do to help reduced the build time is use a config-setting to point to the already built compiled packages so I don't have rebuild them every time. I would like to run "tox run" and override the "conan_cache" value in my config-settings to point to somewhere on my computer where I have all my C dependencies already compiled. In my mind the command should work something like "tox run -x testenv.config-setting="conan_cache=/some/place/on/my/computer" .

My workaround has been using environment variables for everything I want to use in addition to having pep-517 config-settings.