pushrebase: do not require exchange for getting markers

Summary:
D4865150 and D4934720 aren't effective in our current setup. The direct
cause in the code is because the server couldn't find common marker version:

```
  # old server-side code, returns empty in our current setup
  obsolete.commonversion(bundle2.obsmarkersversion(reply.capabilities))
```

Upon investigation, it's because there is no `exchange` enabled client-side.

But we do want one-way (server->client) markers for the rebased commits, as
long as obsstore is enabled (createmarkers is set, without exchange).

The upstream expects the server to have obsstore enabled, and exchange
enabled, to send markers. Since we are generating markers without an
obsstore (see D4865150), we are on our own way. This diff makes it one step
further.

This diff adds an explicit parameter to the `b2x:rebase` part to tell the
server what obsmarker format the client supports so the server could make a
right decision without relying on the "standard" `reply.capabilities`, which
is affected by the exchange option.

Test Plan: Change the existing test, make sure the old code fails.

Reviewers: #mercurial, durham

Reviewed By: durham

Subscribers: durham, mjpieters

Differential Revision: https://phabricator.intern.facebook.com/D4997972

Signature: t1:4997972:1493848751:14c29654b2e8246bd12a8de8820af5b3773e2fb7

hgext3rd/pushrebase.py

@@ -130,6 +130,25 @@ def getrebasepart(repo, peer, outgoing, onto, newhead):
 
     cg = changegroup.getlocalchangegroupraw(repo, 'push', outgoing)
 
+    # Explicitly notify the server what obsmarker versions the client supports
+    # so the client could receive marker from the server.
+    #
+    # The core mercurial logic will do the right thing (enable obsmarker
+    # capabilities in the pushback bundle) if obsmarker exchange is enabled
+    # client-side.
+    #
+    # But we want the marker without enabling marker exchange, and our server
+    # could reply a marker without exchange or even obsstore enabled. So we
+    # bypass the "standard" way of capabilities check by sending the supported
+    # versions directly in our own part. Note: do not enable "exchange" because
+    # it has an unwanted side effect: pushing markers from client to server.
+    #
+    # "createmarkers" is all we need to be able to write a new marker.
+    if obsolete.isenabled(repo, obsolete.createmarkersopt):
+        obsmarkerversions = '\0'.join(str(v) for v in obsolete.formats)
+    else:
+        obsmarkerversions = ''
+
     # .upper() marks this as a mandatory part: server will abort if there's no
     #  handler
     return bundle2.bundlepart(
@@ -138,6 +157,10 @@ def getrebasepart(repo, peer, outgoing, onto, newhead):
             'onto': onto,
             'newhead': repr(newhead),
         }.items(),
+        advisoryparams={
+            # advisory: (old) server could ignore this without error
+            'obsmarkerversions': obsmarkerversions,
+        }.items(),
         data = cg)
 
 def _checkheads(orig, pushop):
@@ -525,13 +548,20 @@ def _addpushbackchangegroup(repo, reply, outgoing):
     if version != '01':
         cgpart.addparam('version', version)
 
-def _addpushbackobsolete(repo, reply, markers, markerdate):
+def _addpushbackobsolete(repo, reply, markers, markerdate,
+                         clientobsmarkerversions):
     '''adds obsmarkers to reply'''
-    # if the client talks about obsmarkers, send them, regardless of if
-    # obsstore is enabled server-side or not.
-    v = obsolete.commonversion(bundle2.obsmarkersversion(reply.capabilities))
-    if v is None:
+    # experimental config: pushrebase.pushback.obsmarkers
+    # if set to True, the server will not push back obsmarkers.
+    if not repo.ui.configbool('pushrebase', 'pushback.obsmarkers', True):
         return
+
+    # _buildobsolete has hard-coded obsolete._fm1version raw markers, so client
+    # needs to support it, and the reply needs to have the correct capabilities
+    if obsolete._fm1version not in clientobsmarkerversions:
+        return
+    reply.capabilities['obsmarkers'] = ['V1']
+
     flag = 0
     parents = None
     try:
@@ -542,7 +572,8 @@ def _addpushbackobsolete(repo, reply, markers, markerdate):
     except ValueError as exc:
         repo.ui.status(_("can't send obsolete markers: %s") % exc.message)
 
-def _addpushbackparts(op, replacements, markers, markerdate):
+def _addpushbackparts(op, replacements, markers, markerdate,
+                      clientobsmarkerversions):
     '''adds pushback to reply if supported by the client'''
     if (op.records[commonheadsparttype]
         and op.reply
@@ -556,7 +587,8 @@ def _addpushbackparts(op, replacements, markers, markerdate):
             op.repo.ui.warn(_("%s new changeset%s from the server will be "
                               "downloaded\n") % (len(outgoing.missing), plural))
             _addpushbackchangegroup(op.repo, op.reply, outgoing)
-            _addpushbackobsolete(op.repo, op.reply, markers, markerdate)
+            _addpushbackobsolete(op.repo, op.reply, markers, markerdate,
+                                 clientobsmarkerversions)
 
 def resolveonto(repo, ontoarg):
     try:
@@ -568,7 +600,7 @@ def resolveonto(repo, ontoarg):
     # onto is None means don't do rebasing
     return None
 
-@bundle2.parthandler(rebaseparttype, ('onto', 'newhead'))
+@bundle2.parthandler(rebaseparttype, ('onto', 'newhead', 'obsmarkerversions'))
 def bundle2rebase(op, part):
     '''unbundle a bundle2 containing a changegroup to rebase'''
 
@@ -576,6 +608,8 @@ def bundle2rebase(op, part):
 
     bundlefile = None
     bundle = None
+    clientobsmarkerversions = [
+        int(v) for v in params.get('obsmarkerversions', '').split('\0') if v]
     markers = []
     markerdate = util.makedate()
 
@@ -743,7 +777,8 @@ def bundle2rebase(op, part):
     tr.addpostclose('serverrebase-cg-hooks',
                     lambda tr: op.repo._afterlock(runhooks))
 
-    _addpushbackparts(op, replacements, markers, markerdate)
+    _addpushbackparts(op, replacements, markers, markerdate,
+                      clientobsmarkerversions)
 
     for k in replacements.keys():
         replacements[hex(k)] = hex(replacements[k])

tests/test-pushrebase.t

@@ -386,7 +386,7 @@ With evolution enabled, should set obsolescence markers
   > rebase =
   > 
   > [experimental]
-  > evolution = all
+  > evolution = createmarkers
   > EOF
 
   $ cd ../client