fix issue with alias_config removed at MLZ

rotation_z will be automatically assigned to one of a list
of aliases ('unique' entry in frappy_config) but will complain
when this is not unique.

devices.py

@@ -31,7 +31,7 @@ import os
 from os.path import expanduser
 
 from nicos import config, session
-from nicos.core import Override, Param, Moveable, status, POLLER, SIMULATION
+from nicos.core import Override, Param, Moveable, status, POLLER, SIMULATION, DeviceAlias
 from nicos.devices.secop.devices import SecNodeDevice
 from nicos.core import Device, anytype, listof
 from nicos.utils.comparestrings import compare
@@ -108,7 +108,7 @@ class FrappyConfig(Device):
                 aliasnames = [aliasnames]
             for aliasname in aliasnames:
                 aliasdev = session.devices.get(aliasname)
-                if aliasdev:
+                if isinstance(aliasdev, DeviceAlias):
                     result[aliasname] = aliasdev
         return result
 
@@ -143,6 +143,15 @@ class FrappyConfig(Device):
             if isinstance(aliasnames, str):
                 aliasnames = [aliasnames]
             aliascfg = info.get('targets', {})
+            unique = info.get('unique')
+            if unique:
+                aliases = [a for a in unique
+                           if isinstance(session.devices.get(a), DeviceAlias)]
+                if aliases:
+                    if len(aliases) > 1:
+                        raise TypeError(f'do know to which of {aliases} {meaning} to assign to')
+                    alias_config = session.alias_config.setdefault(aliases[0], [])
+                    alias_config.extend(list(aliascfg.items()))
             importance_list = sample_devices.get(meaning, [])
             importance_list.extend([(nr, nam) for nam, nr in aliascfg.items() if nam in session.devices])
             importance_list = sorted(importance_list, reverse=True)

setups/frappy.py

@@ -34,6 +34,7 @@ devices = dict(
             'targets': {'se_mf': 20},
         },
         rotation_z = {
+            'unique': ['a3', 'om'],
             'alias': 'dom',
             'targets': {'se_om': 20, 'se_stickrot': 19},
             'envlist': False,