rebase: scope parent change into a changing_parents context

If we are actually altering the working copy (i.e. we are not in memory), we
should properly scope the working copy update.

hgext/rebase.py

@@ -1513,12 +1513,14 b' def rebasenode(repo, rev, p1, p2, base, '
     p1ctx = repo[p1]
     if wctx.isinmemory():
         wctx.setbase(p1ctx)
+        scope = util.nullcontextmanager
     else:
         if repo[b'.'].rev() != p1:
             repo.ui.debug(b" update to %d:%s\n" % (p1, p1ctx))
             mergemod.clean_update(p1ctx)
         else:
             repo.ui.debug(b" already in destination\n")
+        scope = lambda: repo.dirstate.changing_parents(repo)
         # This is, alas, necessary to invalidate workingctx's manifest cache,
         # as well as other data we litter on it in other places.
         wctx = repo[None]
@@ -1528,6 +1530,7 b' def rebasenode(repo, rev, p1, p2, base, '
     if base is not None:
         repo.ui.debug(b"   detach base %d:%s\n" % (base, repo[base]))
 
+    with scope():
     # See explanation in merge.graft()
     mergeancestor = repo.changelog.isancestor(p1ctx.node(), ctx.node())
     stats = mergemod._update(