Update extruder definition if necessary

CURA-5334

cura/Settings/ExtruderManager.py

@@ -393,10 +393,22 @@ class ExtruderManager(QObject):
                 extruder_train.setNextStack(global_stack)
                 extruders_changed = True
 
+            self._fixSingleExtrusionMahineExtruderDefinition(global_stack)
             if extruders_changed:
                 self.extrudersChanged.emit(global_stack_id)
                 self.setActiveExtruderIndex(0)
 
+    # After 3.4, all single-extrusion machines have their own extruder definition files instead of reusing
+    # "fdmextruder". We need to check a machine here so its extruder definition is correct according to this.
+    def _fixSingleExtrusionMahineExtruderDefinition(self, global_stack):
+        expected_extruder_definition_0_id = global_stack.getMetaDataEntry("machine_extruder_trains")["0"]
+        extruder_stack_0 = global_stack.extruders["0"]
+        if extruder_stack_0.definition.getId() != expected_extruder_definition_0_id:
+            extruder_definition_id = global_stack.getMetaDataEntry("machine_extruder_trains")["0"]
+            container_registry = ContainerRegistry.getInstance()
+            extruder_definition = container_registry.findDefinitionContainers(id = extruder_definition_id)[0]
+            extruder_stack_0.definition = extruder_definition
+
     ##  Get all extruder values for a certain setting.
     #
     #   This is exposed to SettingFunction so it can be used in value functions.