Implement declarative config for compatibility with setuptools declarative config

[jaraco]

Fixes #181

In irc.freenode.net#pylib, Ronny asked about supporting setuptools_scm on setuptools in a declarative config world. This change illustrates how I'd propose for that to happen. Setuptools would expose a new hook, something like

https://gist.github.com/b45998781be03918a21f17da996ee687

And then setuptools_scm would provide a hook into that such as the one (building on all of the existing work already done).

[jaraco]

Still to do:

• Settle on the right hook/API and release changes in setuptools.
• Decide if setuptools_scm needs to support both setup() invocation and this declarative mode.
• If so, implement compatibility protocol.
• Add tests for this new functionality.
• Implement the stubbed config file reader.
• Update docs to describe how to use this preferred functionality.

[RonnyPfannschmidt]

I like this,
the setup keyword can actually stay relatively easy with this,

Could setuptools provide a helper to get the settings section from pyproject.toml

Thanks!

[jaraco]

Unfortunately, setuptools itself doesn't yet have toml (or pyproject.toml) support... but it might be worthwhile for setuptools to own that functionality to avoid plugins needing to own the parsing.

How much harm is it for setuptools_scm to have a dependency (toml)?

[RonnyPfannschmidt]

its a pain for anyone using the legacy support as it will pull in toml via easy_install

so having a toml dependency outside of what setuptools does would be a big blow for backward compat

its possible to make it a extra dependency
but its not clear to me how to make the entrypoint work properly then in all situation

[RonnyPfannschmidt]

@jaraco got thinking again, its easy to have a extra and a optional import, after all - i can sort out most of the pain i believe (bit it would still be much nicer if the toml data was readily available in some way)

[jaraco]

its a pain for anyone using the legacy support as it will pull in toml via easy_install

Are there scenarios where requiring a pure-python source distribution wouldn't work as a simple dependency (as toml installs under easy_install)? I'm not opposed to finding another solution, but I'd like to know what scenario we're seeking to solve.

its easy to have a extra and a optional import

Oh, so setuptools_scm[toml]>=version_with_toml (or similar) would be the requirement specified by setup_requires or PEP 518 build_requires? That sounds feasible.

[RonnyPfannschmidt]

This is shaping up nicely, I like it

[RonnyPfannschmidt]

great work, what about the wip status

[jaraco]

I've got a few more commits to address the docs.

[RonnyPfannschmidt]

thanks for implementing and documenting this

with this fabulous work many are finally free of setup.py

i plan to release mid week after including the ci/pre-commit fixups

[webknjaz]

Looks like you placed the closing backticks too far...

[jaraco]

I wasn't quite sure how to handle that, given that the backticks are in the title. I'm happy to accept edits on it.

[webknjaz]

Oh. I'm not sure either. Could probably try using a link syntax.

[madig]

Just chiming in to say FUCK YEAH. Thanks! One less file lying around 👍