transaction: write pending generated files

Such file are generated with a .pending prefix. It is up to the reader to
implement the necessary logic for reading pending files.

We add a test to ensure pending files are properly cleaned-up in both success and
error cases.

mercurial/transaction.py

@@ -342,6 +342,7 b' class transaction(object):'
             # remove callback since the data will have been flushed
             any = self._pendingcallback.pop(cat)(self)
             self._anypending = self._anypending or any
+        self._anypending |= self._generatefiles(suffix='.pending')
         return self._anypending
 
     @active

tests/test-bundle2-exchange.t

@@ -304,6 +304,15 b' Check final content.'
   6666666666666666666666666666666666666666 5fddd98957c8a54a4d436dfe1da9d87f21a1b97b 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
   7777777777777777777777777777777777777777 32af7686d403cf45b5d95f2d70cebea587ac806a 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
 
+(check that no 'pending' files remain)
+
+  $ ls -1 other/.hg/bookmarks*
+  other/.hg/bookmarks
+  $ ls -1 other/.hg/store/phaseroots*
+  other/.hg/store/phaseroots
+  $ ls -1 other/.hg/store/00changelog.i*
+  other/.hg/store/00changelog.i
+
 Error Handling
 ==============
 
@@ -479,4 +488,12 b' Doing the actual push: hook abort'
   abort: b2x-pretransactionclose.failpush hook exited with status 1
   [255]
 
+(check that no 'pending' files remain)
 
+  $ ls -1 other/.hg/bookmarks*
+  other/.hg/bookmarks
+  $ ls -1 other/.hg/store/phaseroots*
+  other/.hg/store/phaseroots
+  $ ls -1 other/.hg/store/00changelog.i*
+  other/.hg/store/00changelog.i
+