New sysconfig API: Install paths

[FFY00]

Feature or enhancement

We should replace sysconfig.get_paths() with something that can accurately describe the current reality.

Pitch

The new API should:

• Support optional paths (eg. not all schemes can provide a scripts directory)
• Introduce the concept of writable and read-only paths (this should be the default for stdlib for eg.)
• Introduce the concept of active location schemes (eg. posix_user should not be available on virtual environments)

API design

Previous discussion

https://discuss.python.org/t/building-extensions-modules-in-a-post-distutils-world/23938
https://discuss.python.org/t/pep-582-python-local-packages-directory/963/391
https://discuss.python.org/t/linux-distro-patches-to-sysconfig-are-changing-pip-install-prefix-outside-virtual-environments/18240/28
https://discuss.python.org/t/deprecating-the-headers-wheel-data-key/23712

New sysconfig API meta-issue: GH-103480

[pradyunsg]

Support optional paths (eg. not all schemes can provide a scripts directory)

Are there specific examples? What is the usecase for "optional" scheme paths?

[FFY00]

PEP 582 would be a good example in a normal environment. See https://discuss.python.org/t/pep-582-python-local-packages-directory/963/391 for some of the discussion regarding it.

WASM would be a good example of a new type of environment where certain paths, like scripts or include, don't make sense (at the moment at least) ¹.

Footnotes

1. PyScript, for eg., currently returns nonexistent paths in sysconfig.get_paths(). ↩