treemanifest: set requires at repo creation time, ignore config after

The very next changeset will start writing one revlog per directory
when tree manifests are enabled. That is backwards incompatible, so it
requires .hg/requires to be updated. Just like with generaldelta, we
want to update .hg/requires only when the repo is created. Updating
..hg/requires is bad for repos on shared disk. Instead, those who do
want to upgrade a repo to using treemanifest (or manifestv2, etc) can
run

  hg clone --config experimental.treemanifest repo clone


which will create a new repo with the requirement set. Unlike the case
of e.g. generaldelta, it will not rewrite the changesets, since tree
manifests hash differently.

mercurial/localrepo.py

@@ -192,10 +192,11 b' class locallegacypeer(localpeer):'
 
 class localrepository(object):
 
-    supportedformats = set(('revlogv1', 'generaldelta', 'manifestv2'))
+    supportedformats = set(('revlogv1', 'generaldelta', 'treemanifest',
+                            'manifestv2'))
     _basesupported = supportedformats | set(('store', 'fncache', 'shared',
                                              'dotencode'))
-    openerreqs = set(('revlogv1', 'generaldelta', 'manifestv2'))
+    openerreqs = set(('revlogv1', 'generaldelta', 'treemanifest', 'manifestv2'))
     filtername = None
 
     # a list of (ui, featureset) functions.
@@ -259,6 +260,8 b' class localrepository(object):'
                     )
                 if self.ui.configbool('format', 'generaldelta', False):
                     self.requirements.add("generaldelta")
+                if self.ui.configbool('experimental', 'treemanifest', False):
+                    self.requirements.add("treemanifest")
                 if self.ui.configbool('experimental', 'manifestv2', False):
                     self.requirements.add("manifestv2")
             else:
@@ -348,9 +351,6 b' class localrepository(object):'
         manifestcachesize = self.ui.configint('format', 'manifestcachesize')
         if manifestcachesize is not None:
             self.svfs.options['manifestcachesize'] = manifestcachesize
-        usetreemanifest = self.ui.configbool('experimental', 'treemanifest')
-        if usetreemanifest is not None:
-            self.svfs.options['usetreemanifest'] = usetreemanifest
 
     def _writerequirements(self):
         scmutil.writerequires(self.vfs, self.requirements)

mercurial/manifest.py

@@ -760,7 +760,7 b' class manifest(revlog.revlog):'
         opts = getattr(opener, 'options', None)
         if opts is not None:
             cachesize = opts.get('manifestcachesize', cachesize)
-            usetreemanifest = opts.get('usetreemanifest', usetreemanifest)
+            usetreemanifest = opts.get('treemanifest', usetreemanifest)
             usemanifestv2 = opts.get('manifestv2', usemanifestv2)
         self._mancache = util.lrucachedict(cachesize)
         revlog.revlog.__init__(self, opener, "00manifest.i")