shelve: bundle using bundle2 if repository is general delta (issue4862)

This will prevent expensive delta computation on bundling and is similar to what we do
for strip backup.

hgext/shelve.py

@@ -106,8 +106,18 b' class shelvedfile(object):'
         return bundlerepo.bundlerepository(self.repo.baseui, self.repo.root,
                                            self.vfs.join(self.fname))
     def writebundle(self, bases, node):
-        cg = changegroup.changegroupsubset(self.repo, bases, [node], 'shelve')
-        changegroup.writebundle(self.ui, cg, self.fname, 'HG10BZ', self.vfs)
+        btype = 'HG10BZ'
+        cgversion = '01'
+        compression = None
+        if 'generaldelta' in self.repo.requirements:
+            btype = 'HG20'
+            cgversion = '02'
+            compression = 'BZ'
+
+        cg = changegroup.changegroupsubset(self.repo, bases, [node], 'shelve',
+                                           version=cgversion)
+        changegroup.writebundle(self.ui, cg, self.fname, btype, self.vfs,
+                                compression=compression)
 
 class shelvedstate(object):
     """Handle persistence during unshelving operations.

tests/test-shelve.t

@@ -954,3 +954,49 b' shelve --patch and shelve --stat should '
   abort: cannot find shelf nonexistentshelf
   [255]
 
+  $ cd ..
+
+Shelve from general delta repo uses bundle2 on disk
+--------------------------------------------------
+
+no general delta
+
+  $ hg clone --pull repo bundle1 --config format.generaldelta=0
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 5 changesets with 8 changes to 6 files
+  updating to branch default
+  6 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ cd bundle1
+  $ echo babar > jungle
+  $ hg add jungle
+  $ hg shelve
+  shelved as default
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg debugbundle .hg/shelved/*.hg
+  7e30d8ac6f23cfc84330fd7e698730374615d21a
+  $ cd ..
+
+with general delta
+
+  $ hg clone --pull repo bundle2 --config format.generaldelta=1
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 5 changesets with 8 changes to 6 files
+  updating to branch default
+  6 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ cd bundle2
+  $ echo babar > jungle
+  $ hg add jungle
+  $ hg shelve
+  shelved as default
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg debugbundle .hg/shelved/*.hg
+  Stream params: {'Compression': 'BZ'}
+  changegroup -- "{'version': '02'}"
+      7e30d8ac6f23cfc84330fd7e698730374615d21a
+  $ cd ..