Add a dedicated stack class for per-object settings

CURA-4186

Add a dedicated stack class PerObjectContainerStack for per-object
settings to evaluate limit_to_extruder values correctly.

cura/Settings/PerObjectContainerStack.py

@@ -0,0 +1,49 @@
+from typing import Any, Optional
+
+from UM.Decorators import override
+from UM.Logger import Logger
+from UM.Settings.Interfaces import PropertyEvaluationContext
+from UM.Settings.ContainerStack import ContainerStack
+
+
+class PerObjectContainerStack(ContainerStack):
+
+    @override(ContainerStack)
+    def getProperty(self, key: str, property_name: str, context: Optional[PropertyEvaluationContext] = None) -> Any:
+        if context is None:
+            context = PropertyEvaluationContext()
+        context.pushContainer(self)
+
+        # this import has to be here otherwise there will be a circular import loop
+        from cura.CuraApplication import CuraApplication
+        global_stack = CuraApplication.getInstance().getGlobalContainerStack()
+
+        # Handle the "limit_to_extruder" property.
+        limit_to_extruder = super().getProperty(key, "limit_to_extruder", context)
+        if limit_to_extruder is not None:
+            limit_to_extruder = str(limit_to_extruder)
+
+        # if this stack has the limit_to_extruder "not overriden", use the original limit_to_extruder as the current
+        # limit_to_extruder, so the values retrieved will be from the perspective of the original limit_to_extruder
+        # stack.
+        if limit_to_extruder == "-1":
+            if 'original_limit_to_extruder' in context.context:
+                limit_to_extruder = context.context['original_limit_to_extruder']
+
+        if limit_to_extruder is not None and limit_to_extruder != "-1" and limit_to_extruder in global_stack.extruders:
+            # set the original limit_to_extruder if this is the first stack that has a non-overriden limit_to_extruder
+            if 'original_limit_to_extruder' not in context.context:
+                context.context['original_limit_to_extruder'] = limit_to_extruder
+
+            if super().getProperty(key, "settable_per_extruder", context):
+                result = global_stack.extruders[str(limit_to_extruder)].getProperty(key, property_name, context)
+                if result is not None:
+                    context.popContainer()
+                    return result
+            else:
+                Logger.log("e", "Setting {setting} has limit_to_extruder but is not settable per extruder!", setting = key)
+
+        result = super().getProperty(key, property_name, context)
+        context.popContainer()
+        return result
+