rebase: abort cleanly when we encounter a damaged rebasestate (issue4155)

hgext/rebase.py

@@ -658,6 +658,7 b' def clearstatus(repo):'
 def restorestatus(repo):
     'Restore a previously stored status'
     try:
+        keepbranches = None
         target = None
         collapse = False
         external = nullrev
@@ -687,6 +688,10 b' def restorestatus(repo):'
                     state[repo[oldrev].rev()] = int(newrev)
                 else:
                     state[repo[oldrev].rev()] = repo[newrev].rev()
+
+        if keepbranches is None:
+            raise util.Abort(_('.hg/rebasestate is incomplete'))
+
         skipped = set()
         # recompute the set of skipped revs
         if not collapse:

tests/test-rebase-abort.t

@@ -13,6 +13,16 b''
   $ hg init a
   $ cd a
 
+  $ touch .hg/rebasestate
+  $ hg sum
+  parent: -1:000000000000 tip (empty repository)
+  branch: default
+  commit: (clean)
+  update: (current)
+  abort: .hg/rebasestate is incomplete
+  [255]
+  $ rm .hg/rebasestate
+
   $ echo c1 > common
   $ hg add common
   $ hg ci -m C1