Use global instance of PythonSetup for resolve requirements task base

[CMLivingston]

Fix for #7625. The resolve requirements task base module was using a scoped instance of PythonSetup, breaking the ./pants repl --python-setup-interpreter-constraints=<constraints> <target> usage pattern.

Solution

Use the global instance of PythonSetup so we can still use global options that cut across all interpreter selection-related mechanisms.

Result

Users that set non-scoped options on PythonSetup are once again able to apply them globally across tasks that use PythonSetup.

[jsirois]

Don't forget to work off your fork if pantsbuild/pants - personal branches should not be pushed to pantsbuild/pants.

[CMLivingston]

ah shoot, sorry about that. My computer got wiped and I misconfigured my remotes. I'll delete it after this lands.

[CMLivingston]

I am unable to re-kick the two failed travis builds. They appear unrelated, would someone mind restarting those for me please?

[stuhood]

@CMLivingston : They're looking green now. Can ignore the push build.

[stuhood]

I think that this represents a breaking change... maybe one that we're ok with though.

A middle ground might be to leave behind the old scoped dep as deprecated (via PythonSetup.scoped(cls, removal_version=.., removal_hint=..)), and just not use it?:

pants/src/python/pants/subsystem/subsystem.py

Lines 52 to 61 in 3742edb

	@classmethod
	def scoped(cls, optionable, removal_version=None, removal_hint=None):
	"""Returns a dependency on this subsystem, scoped to `optionable`.
	:param removal_version: An optional deprecation version for this scoped Subsystem dependency.
	:param removal_hint: An optional hint to accompany a deprecation removal_version.
	Return value is suitable for use in SubsystemClientMixin.subsystem_dependencies().
	"""
	return SubsystemDependency(cls, optionable.options_scope, removal_version, removal_hint)

[CMLivingston]

After discussing with @stuhood, I'm going to leave as is due to the option overriding going on if we try to deprecate the scoped dependency alongside a global subsystem dependency.

[stuhood]

Have marked this for 1.16.x.