Rigify: fix nonsensical default parent for pole controls.

Instead of collecting all possible parents in a list, use
buckets indexed by the owning rig, so that parents injected
by other rigs are ordered correctly. Otherwise the Head
parent injected into the spine hierarchy gets in the way.

rigify/utils/switch_parent.py

@@ -13,7 +13,8 @@ from .misc import map_list, map_apply
 from ..base_rig import *
 from ..base_generate import GeneratorPlugin
 
-from itertools import count, repeat
+from collections import defaultdict
+from itertools import count, repeat, chain
 
 def _auto_call(value):
     if callable(value):
@@ -45,7 +46,7 @@ class SwitchParentBuilder(GeneratorPlugin, MechanismUtilityMixin):
 
         self.child_list = []
         self.global_parents = []
-        self.local_parents = []
+        self.local_parents = defaultdict(list)
         self.child_map = {}
         self.frozen = False
 
@@ -82,7 +83,7 @@ class SwitchParentBuilder(GeneratorPlugin, MechanismUtilityMixin):
         if is_global:
             self.global_parents.append(entry)
         else:
-            self.local_parents.append(entry)
+            self.local_parents[id(rig)].append(entry)
 
 
     def build_child(self, rig, bone, *, use_parent_mch=True, **options):
@@ -176,16 +177,28 @@ class SwitchParentBuilder(GeneratorPlugin, MechanismUtilityMixin):
 
             child[name] = value
 
+    def get_rig_parent_candidates(self, rig):
+        candidates = []
+
+        # Build a list in parent hierarchy order
+        while rig:
+            candidates.append(self.local_parents[id(rig)])
+            rig = rig.rigify_parent
+
+        candidates.append(self.global_parents)
+
+        return list(chain.from_iterable(reversed(candidates)))
+
     def generate_bones(self):
         self.frozen = True
-        self.parent_list = self.global_parents + self.local_parents
+        self.parent_list = self.global_parents + list(chain.from_iterable(self.local_parents.values()))
 
         # Link children to parents
         for child in self.child_list:
             child_rig = child['context_rig'] or child['rig']
             parents = []
 
-            for parent in self.parent_list:
+            for parent in self.get_rig_parent_candidates(child_rig):
                 if parent['rig'] is child_rig:
                     if parent['exclude_self'] or child['exclude_self']:
                         continue