push: acquire local 'wlock' if "pushback" is expected (BC) (issue4596)

If the client allows "pushback", the bundle2 served back by the server may
contains parts that will write to the repository. Such parts may require the
'wlock' (eg: bookmark) so we acquire it in advance to make sure it got acquired
before the 'lock'.

mercurial/exchange.py

@@ -201,8 +201,13 b' def push(repo, remote, force=False, revs'
     if not pushop.remote.canpush():
         raise util.Abort(_("destination does not support push"))
     # get local lock as we might write phase data
-    locallock = None
+    localwlock = locallock = None
     try:
+        # bundle2 push may receive a reply bundle touching bookmarks or other
+        # things requiring the wlock. Take it now to ensure proper ordering.
+        maypushback = pushop.ui.configbool('experimental', 'bundle2.pushback')
+        if _canusebundle2(pushop) and maypushback:
+            localwlock = pushop.repo.wlock()
         locallock = pushop.repo.lock()
         pushop.locallocked = True
     except IOError, err:
@@ -242,6 +247,8 b' def push(repo, remote, force=False, revs'
             pushop.trmanager.release()
         if locallock is not None:
             locallock.release()
+        if localwlock is not None:
+            localwlock.release()
 
     return pushop
 

tests/test-bundle2-pushback.t

@@ -91,7 +91,6 b' With config'
   $ hg push
   pushing to ssh://user@dummy/server
   searching for changes
-  "wlock" acquired after "lock" at: */mercurial/bookmarks.py:259 (pushbookmark) (glob)
   remote: adding changesets
   remote: adding manifests
   remote: adding file changes