revlog: specify checkambig at writing to avoid file stat ambiguity This allows revlog-style files to be written out with checkambig=True easily. Because avoiding file stat ambiguity is needed only for filecache-ed manifest and changelog, this patch does: - use False for default value of checkambig - focus only on writing changes of index file out This patch also adds optional argument checkambig to _divert/_delay for changelog, to safely accept checkambig specified in revlog layer. But this argument can be fully ignored, because: - changes are written into other than index file, if name != target - changes are never written into index file, otherwise (into pending file by _divert, or into in-memory buffer by _delay) This is a part of ExactCacheValidationPlan. https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

--- a/mercurial/changelog.py	Thu Sep 22 21:51:57 2016 +0900
+++ b/mercurial/changelog.py	Thu Sep 22 21:51:58 2016 +0900
@@ -124,7 +124,7 @@
 
 def _divertopener(opener, target):
     """build an opener that writes in 'target.a' instead of 'target'"""
-    def _divert(name, mode='r'):
+    def _divert(name, mode='r', checkambig=False):
         if name != target:
             return opener(name, mode)
         return opener(name + ".a", mode)
@@ -132,7 +132,7 @@
 
 def _delayopener(opener, target, buf):
     """build an opener that stores chunks in 'buf' instead of 'target'"""
-    def _delay(name, mode='r'):
+    def _delay(name, mode='r', checkambig=False):
         if name != target:
             return opener(name, mode)
         return appender(opener, name, mode, buf)