rebase: avoid converting from nodes to revnums twice

In the case where the node has successors, but none of them is an
ancestor of the destination, we would iterate over the successor nodes
twice, check if they're in the repo and convert them to revnums. I
doubt it's a measureable cost, but it gets simpler this way too.

Differential Revision: https://phab.mercurial-scm.org/D3941

hgext/rebase.py

@@ -1869,19 +1869,17 b' def _computeobsoletenotrebased(repo, reb'
             # no successor
             obsoletenotrebased[srcrev] = None
         else:
-            destnode = cl.node(destmap[srcrev])
-            for succnode in successors:
-                if succnode not in nodemap:
-                    continue
-                if cl.isancestor(succnode, destnode):
-                    obsoletenotrebased[srcrev] = nodemap[succnode]
+            dstrev = destmap[srcrev]
+            succrevs = [nodemap[s] for s in successors if s in nodemap]
+            for succrev in succrevs:
+                if cl.isancestorrev(succrev, dstrev):
+                    obsoletenotrebased[srcrev] = succrev
                     break
             else:
                 # If 'srcrev' has a successor in rebase set but none in
                 # destination (which would be catched above), we shall skip it
                 # and its descendants to avoid divergence.
-                if any(nodemap[s] in destmap for s in successors
-                       if s in nodemap):
+                if any(s in destmap for s in succrevs):
                     obsoletewithoutsuccessorindestination.add(srcrev)
 
     return (