Add more flexibility in Distribution.finalize_options for plugins

[jaraco]

In coherent-oss/coherent.licensed#1, I've touched on a limitation of the plugin integration for setuptools.finalize_distribution_options.

Although the integration allows for plugins to specify the "order" that these finalizers run, there are subsequent finalization actions that happen after the finalizers:

• parsing config files
• handling command line options

As a result, it's not possible for a plugin using this entry point to customize any behavior that relies on those settings.

I propose instead that parsing config files and command-line options should also be treated as finalizers so that their behavior can be integrated into the plugin mechanism.

[abravalheri]

I propose instead that parsing config files and command-line options should also be treated as finalizers so that their behavior can be integrated into the plugin mechanism.

This possibly requires changes in distutils.core.setup, which may be backwards incompatible (but it is hard to tell).

Have you considered introducing a new entry-point for this? This would be mostly backwards compatible. (I think that ideally we want to restrain the proliferation of entry-points and APIs, but in this case it may make sense).

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On a related note:

In #2652 and #3415 a series of limitations and "wishes" about finalize_distribution_options, e.g., allowing finalizes to be opted-in/opted-out and passing configurations has been requested.