largefiles: add tr backup for largefilesdirstate

This will help us in automatically restoring the largefilesdirstate if a
transaction is rolled back.

Differential Revision: https://phab.mercurial-scm.org/D11611

hgext/largefiles/lfutil.py

@@ -195,6 +195,8 b' class largefilesdirstate(dirstate.dirsta'
         # (1) disable PENDING mode always
         #     (lfdirstate isn't yet managed as a part of the transaction)
         # (2) avoid develwarn 'use dirstate.write with ....'
+        if tr:
+            tr.addbackup(b'largefiles/dirstate', location=b'plain')
         super(largefilesdirstate, self).write(None)
 
 

tests/test-largefiles-cache.t

@@ -185,10 +185,12 b' conditional above.'
 
   $ find share_dst/.hg/largefiles/* | sort
   share_dst/.hg/largefiles/dirstate
+  share_dst/.hg/largefiles/undo.backup.dirstate
 
   $ find src/.hg/largefiles/* | egrep "(dirstate|$hash)" | sort
   src/.hg/largefiles/dirstate
   src/.hg/largefiles/e2fb5f2139d086ded2cb600d5a91a196e76bf020
+  src/.hg/largefiles/undo.backup.dirstate
 
 Verify that backwards compatibility is maintained for old storage layout
   $ mv src/.hg/largefiles/$hash share_dst/.hg/largefiles