changegroup: don't limit cgv4 to revlogv2 repos

To help the transition from revlogv1 to revlogv2, we need to be able to enable
cgv4 for revlogv1 repos, so that revlogv2 clients can handle adding/removing
sidedata over the wire.

Differential Revision: https://phab.mercurial-scm.org/D10342

mercurial/changegroup.py

@@ -1689,11 +1689,14 b' def allsupportedversions(repo):'
         #
         # (or even to push subset of history)
         needv03 = True
-    has_revlogv2 = requirements.REVLOGV2_REQUIREMENT in repo.requirements
-    if not has_revlogv2:
-        versions.discard(b'04')
     if not needv03:
         versions.discard(b'03')
+    want_v4 = (
+        repo.ui.configbool(b'experimental', b'changegroup4')
+        or requirements.REVLOGV2_REQUIREMENT in repo.requirements
+    )
+    if not want_v4:
+        versions.discard(b'04')
     return versions
 
 

mercurial/configitems.py

@@ -904,6 +904,11 b' coreconfigitem('
 )
 coreconfigitem(
     b'experimental',
+    b'changegroup4',
+    default=False,
+)
+coreconfigitem(
+    b'experimental',
     b'cleanup-as-archived',
     default=False,
 )