Graduate Docker backend from experimental status.

[kaos]

The Docker backend was introduced in Pantsbuild 2.7.0. It is now proven to be a functional backend for many common Docker use cases.

[Eric-Arellano]

Woohoo!!! Epic

We can provide a much nicer upgrade experience for users by still keeping the experimental backend in 2.10. You'll have a register.py in both the old place and new one. (If DRY bothers you, you can import from the new stable file)

There is probably a more elegant way to do this, but you can then add a function similar to this, and call it at the two call sites

pants/src/python/pants/option/global_options.py

Lines 1658 to 1664 in 27f23db

	def maybe_warn_python_macros_deprecation(bootstrap_options: OptionValueContainer) -> None:
	if (
	bootstrap_options.is_default("use_deprecated_python_macros")
	and "pants.backend.python" in bootstrap_options.backend_packages
	):
	warn_or_error(
	"2.11.0.dev0",

I plan to possibly stabilize PyUpgrade & Autoflake, so I'll piggy back off of this helper.

There is probably a more elegant way to do this

Imo, quick and dirty gets the job done here. It's temporary code and this isn't used by plugin authors. End users don't care how we implement the deprecation.

[Eric-Arellano]

Oh! Also init/BUILD and generate_docs.py need updates :)

[kaos]

Oh! Also init/BUILD and generate_docs.py need updates :)

Eh, look again ;)

[kaos]

I didn't see the need for a custom deprecation method, I simply used the @deprecated on the rules in the experimental register module.

Gives me:

22:21:15.20 [WARN] DEPRECATED: pants.backend.experimental.docker.register.rules() will be removed in version 2.11.0.dev0.

The `pants.backend.experimental.docker` backend has graduated. Use `pants.backend.docker` instead.

When used :)

[Eric-Arellano]

Oh cool! Perfect.