Bug in version solver when using a hashable object to represent a package, not just a string.

[Greedquest]

I believe it's this line:

mixology/mixology/version_solver.py

Line 130 in 067c5ae

changed.add(str(self._propagate_incompatibility(root_cause)))

self._propagate_incompatibility will return the _conflict type which is the hashable type used to represent a package (in my usecase this is not a string). The line converts it to str which is a problem since then it is no longer a valid key in the self._incompatibilities dictionary (line 113 of the same function).

mixology/mixology/version_solver.py

Lines 98 to 133 in 067c5ae

	def _propagate(self, package): # type: (Hashable) -> None
	"""
	Performs unit propagation on incompatibilities transitively
	related to package to derive new assignments for _solution.
	"""
	changed = set()
	changed.add(package)
	while changed:
	package = changed.pop()
	# Iterate in reverse because conflict resolution tends to produce more
	# general incompatibilities as time goes on. If we look at those first,
	# we can derive stronger assignments sooner and more eagerly find
	# conflicts.
	for incompatibility in reversed(self._incompatibilities[package]):
	result = self._propagate_incompatibility(incompatibility)
	if result is _conflict:
	# If the incompatibility is satisfied by the solution, we use
	# _resolve_conflict() to determine the root cause of the conflict as a
	# new incompatibility.
	#
	# It also backjumps to a point in the solution
	# where that incompatibility will allow us to derive new assignments
	# that avoid the conflict.
	root_cause = self._resolve_conflict(incompatibility)
	# Back jumping erases all the assignments we did at the previous
	# decision level, so we clear [changed] and refill it with the
	# newly-propagated assignment.
	changed.clear()
	changed.add(str(self._propagate_incompatibility(root_cause)))
	break
	elif result is not None:
	changed.add(result)