fsmonitor: use vfs instead of opener (issue5938) "opener" of localrepository object was dropped at Mercurial 4.3 (or a7e210167c28). "vfs" should be used instead. wlock is required to write into a file under .hg directory. For efficiency, we should change _cmpsets() from: 1. acquire wlock 2. open log file under .hg directory with write mode 3. compare between result of watchman and Mercurial's dirstate logic 4. write out error info into a file, if error is detected 5. release wlock to: 1. compare between result of watchman and Mercurial's dirstate logic 2. acquire wlock, if error is detected 3. open and write error info into a file 4. release wlock But this is another issue.