[PATCH 2 of 3] writebundle: add a compression argument for the bundle2 case

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1443562900 25200
#      Tue Sep 29 14:41:40 2015 -0700
# Node ID 405450625fe8de8f75f66f05b10be3c6a9a93b62
# Parent  4e5c7e8778bfa9114d7e37719cb2009d5a9d284b
writebundle: add a compression argument for the bundle2 case

Bundle2 compression is more complex than the bundle1 one. Therefore it is
handler by the bundler himself. Moreover, on-disk bundle2 will probably have a
large number of flavor so simply adding a new "format" for it does not seems the
way to go.

This will be used in the next changeset to compression bundle2 strip backup>

diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -90,11 +90,11 @@ bundletypes = {
 }
 
 # hgweb uses this list to communicate its preferred type
 bundlepriority = ['HG10GZ', 'HG10BZ', 'HG10UN']
 
-def writebundle(ui, cg, filename, bundletype, vfs=None):
+def writebundle(ui, cg, filename, bundletype, vfs=None, compression=None):
     """Write a bundle file and return its filename.
 
     Existing files will not be overwritten.
     If no filename is specified, a temporary file is created.
     bz2 compression can be turned off.
@@ -115,15 +115,18 @@ def writebundle(ui, cg, filename, bundle
         cleanup = filename
 
         if bundletype == "HG20":
             from . import bundle2
             bundle = bundle2.bundle20(ui)
+            bundle.setcompression(compression)
             part = bundle.newpart('changegroup', data=cg.getchunks())
             part.addparam('version', cg.version)
             z = util.compressors[None]()
             chunkiter = bundle.getchunks()
         else:
+            # compression argument is only for the bundle2 case
+            assert compression is None
             if cg.version != '01':
                 raise util.Abort(_('old bundle types only supports v1 '
                                    'changegroups'))
             header, comp = bundletypes[bundletype]
             fh.write(header)