diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -47,7 +47,7 @@ from . import (
 
 class request(object):
     def __init__(self, args, ui=None, repo=None, fin=None, fout=None,
-                 ferr=None):
+                 ferr=None, prereposetups=None):
         self.args = args
         self.ui = ui
         self.repo = repo
@@ -57,6 +57,10 @@ class request(object):
         self.fout = fout
         self.ferr = ferr
 
+        # reposetups which run before extensions, useful for chg to pre-fill
+        # low-level repo state (for example, changelog) before extensions.
+        self.prereposetups = prereposetups or []
+
     def _runexithandlers(self):
         exc = None
         handlers = self.ui._exithandlers
@@ -875,7 +879,8 @@ def _dispatch(req):
                 repo.ui.ferr = ui.ferr
             else:
                 try:
-                    repo = hg.repository(ui, path=path)
+                    repo = hg.repository(ui, path=path,
+                                         presetupfuncs=req.prereposetups)
                     if not repo.local():
                         raise error.Abort(_("repository '%s' is not local")
                                           % path)
diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -148,10 +148,12 @@ def openpath(ui, path):
 # a list of (ui, repo) functions called for wire peer initialization
 wirepeersetupfuncs = []
 
-def _peerorrepo(ui, path, create=False):
+def _peerorrepo(ui, path, create=False, presetupfuncs=None):
     """return a repository object for the specified path"""
     obj = _peerlookup(path).instance(ui, path, create)
     ui = getattr(obj, "ui", ui)
+    for f in presetupfuncs or []:
+        f(ui, obj)
     for name, module in extensions.extensions(ui):
         hook = getattr(module, 'reposetup', None)
         if hook:
@@ -161,9 +163,9 @@ def _peerorrepo(ui, path, create=False):
             f(ui, obj)
     return obj
 
-def repository(ui, path='', create=False):
+def repository(ui, path='', create=False, presetupfuncs=None):
     """return a repository object for the specified path"""
-    peer = _peerorrepo(ui, path, create)
+    peer = _peerorrepo(ui, path, create, presetupfuncs=presetupfuncs)
     repo = peer.local()
     if not repo:
         raise error.Abort(_("repository '%s' is not local") %