rebase: properly handle chains of markers with missing nodes

As obsolescence markers can contains unknown nodes and 'allsuccessors' returns
them, we have to protect again that when looking for successors of the rebase
set in the destination.

Test have been expanded to catch that.

hgext/rebase.py

@@ -1167,7 +1167,10 b' def _computeobsoletenotrebased(repo, reb'
         if n.obsolete():
             node = cl.node(r)
             for s in obsolete.allsuccessors(repo.obsstore, [node]):
-                allsuccessors[cl.rev(s)] = cl.rev(node)
+                try:
+                    allsuccessors[cl.rev(s)] = cl.rev(node)
+                except LookupError:
+                    pass
 
     if allsuccessors:
         # Look for successors of obsolete nodes to be rebased among

tests/test-rebase-obsolete.t

@@ -590,3 +590,51 b' Test hidden changesets in the rebase set'
   note: not rebasing 14:9ad579b4a5de "I", already in destination as 17:fc37a630c901 "K"
   rebasing 15:5ae8a643467b "J"
 
+  $ cd ..
+
+Skip obsolete changeset even with multiple hops
+-----------------------------------------------
+
+setup
+
+  $ hg init obsskip
+  $ cd obsskip
+  $ cat << EOF >> .hg/hgrc
+  > [experimental]
+  > rebaseskipobsolete = True
+  > [extensions]
+  > strip =
+  > EOF
+  $ echo A > A
+  $ hg add A
+  $ hg commit -m A
+  $ echo B > B
+  $ hg add B
+  $ hg commit -m B0
+  $ hg commit --amend -m B1
+  $ hg commit --amend -m B2
+  $ hg up --hidden 'desc(B0)'
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ echo C > C
+  $ hg add C
+  $ hg commit -m C
+
+Rebase finds its way in a chain of marker
+
+  $ hg rebase -d 'desc(B2)'
+  note: not rebasing 1:a8b11f55fb19 "B0", already in destination as 3:261e70097290 "B2"
+  rebasing 4:212cb178bcbb "C" (tip)
+
+Even when the chain include missing node
+
+  $ hg up --hidden 'desc(B0)'
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ echo D > D
+  $ hg add D
+  $ hg commit -m D
+  $ hg --hidden strip -r 'desc(B1)'
+  saved backup bundle to $TESTTMP/obsskip/.hg/strip-backup/86f6414ccda7-b1c452ee-backup.hg (glob)
+
+  $ hg rebase -d 'desc(B2)'
+  note: not rebasing 1:a8b11f55fb19 "B0", already in destination as 2:261e70097290 "B2"
+  rebasing 5:1a79b7535141 "D" (tip)