Fix memoization of CoarsenedTarget.closure

[stuhood]

Memoization of CoarsenedTargets.closure() relies on shared memoization across a walk in each CoarsenedTarget. That memoization was not working.

Fixes #17509.

[danxmoran]

Haven't fully grokked the invariants of CTs yet: should we test for overlapping members between CTs as well? Or is that not a situation we can get into?

[stuhood]

No: that should be impossible due to how CTs are constructed. And that bit has existing tests:

pants/src/python/pants/engine/internals/graph_test.py

Lines 370 to 449 in 83b5f04

	def test_coarsened_targets(transitive_targets_rule_runner: RuleRunner) -> None:
	"""CoarsenedTargets should "coarsen" a cycle into a single CoarsenedTarget instance."""
	transitive_targets_rule_runner.write_files(
	{
	"dep.txt": "",
	"t1.txt": "",
	"t2.txt": "",
	# Cycles are only tolerated for file-level targets like `python_source`.
	# TODO(#12871): Stop relying on only generated targets having cycle tolerance.
	"BUILD": dedent(
	"""\
	generator(name='dep', sources=['dep.txt'])
	generator(name='t1', sources=['t1.txt'], dependencies=['dep.txt:dep', 't2.txt:t2'])
	generator(name='t2', sources=['t2.txt'], dependencies=['t1.txt:t1'])
	"""
	),
	}
	)
	def assert_coarsened(
	a: Address, expected_members: List[Address], expected_dependencies: List[Address]
	) -> None:
	coarsened_targets = transitive_targets_rule_runner.request(
	CoarsenedTargets,
	[Addresses([a])],
	)
	assert sorted(t.address for t in coarsened_targets[0].members) == expected_members
	# NB: Only the direct dependencies are compared.
	assert (
	sorted(d.address for ct in coarsened_targets[0].dependencies for d in ct.members)
	== expected_dependencies
	)
	# Non-file-level targets are already validated to not have cycles, so they coarsen to
	# themselves.
	assert_coarsened(
	Address("", target_name="dep"),
	[Address("", target_name="dep")],
	[Address("", relative_file_path="dep.txt", target_name="dep")],
	)
	assert_coarsened(
	Address("", target_name="t1"),
	[Address("", target_name="t1")],
	[
	Address("", relative_file_path="t1.txt", target_name="t1"),
	Address("", relative_file_path="t2.txt", target_name="t2"),
	],
	)
	assert_coarsened(
	Address("", target_name="t2"),
	[Address("", target_name="t2")],
	[
	Address("", relative_file_path="t1.txt", target_name="t1"),
	Address("", relative_file_path="t2.txt", target_name="t2"),
	],
	)
	# File-level targets not involved in cycles coarsen to themselves.
	assert_coarsened(
	Address("", relative_file_path="dep.txt", target_name="dep"),
	[Address("", relative_file_path="dep.txt", target_name="dep")],
	[],
	)
	# File-level targets involved in cycles will coarsen to the cycle, and have only dependencies
	# outside of the cycle.
	cycle_files = [
	Address("", relative_file_path="t1.txt", target_name="t1"),
	Address("", relative_file_path="t2.txt", target_name="t2"),
	]
	assert_coarsened(
	Address("", relative_file_path="t1.txt", target_name="t1"),
	cycle_files,
	[Address("", relative_file_path="dep.txt", target_name="dep")],
	)
	assert_coarsened(
	Address("", relative_file_path="t2.txt", target_name="t2"),
	cycle_files,
	[Address("", relative_file_path="dep.txt", target_name="dep")],
	)

[danxmoran]

Confirmed it's working in practice via pylint on Color's repo