state: automatically assign machines to subsidiary units from their principal units.

state/machine.go

 // launchpad.net/juju/state
 //
 // Copyright (c) 2011-2012 Canonical Ltd.
 
 package state
 
 import (
         "fmt"
         "launchpad.net/juju-core/juju/state/presence"
         "path"
@@ skipping 58 matching lines @@
 func (m *Machine) Units() ([]*Unit, error) {
         topology, err := readTopology(m.st.zk)
         if err != nil {
                 return nil, err
         }
         keys := topology.UnitsForMachine(m.key)
         units := make([]*Unit, len(keys))
         for i, key := range keys {
                 units[i], err = m.st.unitFromKey(topology, key)
                 if err != nil {
-                        // If UnitsForMachine is returning keys that don't
-                        // exist, then something is badly wrong.
-                        panic(err)
+                        return nil, fmt.Errorf("inconsistent topology: %v", err)
                 }
         }
         return units, nil
 }
 
 // SetInstanceId sets the provider specific machine id for this machine.
 func (m *Machine) SetInstanceId(id string) error {
         config, err := readConfigNode(m.st.zk, m.zkPath())
         if err != nil {
                 return err
@@ skipping 33 matching lines @@
         if i < 0 || err != nil {
                 panic("keySeq: invalid key: " + key)
         }
         return int(id64)
 }
 
 // machineKey returns the machine key corresponding to machineId.
 func machineKey(machineId int) string {
         return fmt.Sprintf("machine-%010d", machineId)
 }