Rudder

If we do a partial promise regeneration, some node may have their new promises in the folder
/path/to/relay.new/path/to/node

rather than the good old /path/to/relay/path/to/node

More presillely, we have the following case to manage (node3 was removed in the generation):

1/ Relay and all nodes updated (historical defautl behaviour)

Generation gives:

relay/
  relay_promises
  share/{ node1, node2, node3 }
relay.new/
  relay_promises
  share/{ node1.new, node2.new }

We want ([U] means updated):

relay/
  relay_promises [U]
  share/{ node1 [U], node2 [U] }

2/ Relay promises not updated, some children updated:

Generation gives:

relay/
  relay_promises
  share/{ node1, node2, node3 }
relay.new/
  share/{ node1.new }

We want:

relay/
  relay_promises 
  share/{ node1 [U], node2 }

3/ Relay promises updated, some children updated:

Generation gives:

relay/
  relay_promises
  share/{ node1, node2, node3 }
relay.new/
  relay_promises
  share/{ node1.new }

We want:

relay/
  relay_promises [U]
  share/{ node1 [U], node2 }

We see that all the naive scheme of moving or copying can't be used, and that some set union and intersection of nodes modified or not modified must be done.