merge: fix race that could cause wrong size in dirstate The problem is that hg merge/update/etc work the following way: 1. figure out what files to update 2. apply the update to disk 3. apply the update to in-memory dirstate 4. write dirstate where step3 looks at the filesystem and assumes it sees the result of step2. If a file is changed between step2 and step3, step3 will record incorrect information in the dirstate. I avoid this by passing the size step3 needs directly from step2, for the common path (not implemented for change/delete conflicts for instance). I didn't fix the same race for the exec bit for now, because it's less likely to be problematic and I had trouble due to the fact that the dirstate stores the permissions differently from the manifest (st_mode vs '' 'l' 'x'), in combination with tests that pretend that symlinks are not supported. However, I moved the lstat from step3 to step2, which should tighten the race window markedly, both for the exec bit and for the mtime. Differential Revision: https://phab.mercurial-scm.org/D6475

--- a/mercurial/context.py	Wed Jun 12 13:10:52 2019 -0400
+++ b/mercurial/context.py	Mon May 27 16:55:46 2019 -0400
@@ -1766,6 +1766,8 @@
 
     def size(self):
         return self._repo.wvfs.lstat(self._path).st_size
+    def lstat(self):
+        return self._repo.wvfs.lstat(self._path)
     def date(self):
         t, tz = self._changectx.date()
         try:
@@ -1801,9 +1803,9 @@
 
     def write(self, data, flags, backgroundclose=False, **kwargs):
         """wraps repo.wwrite"""
-        self._repo.wwrite(self._path, data, flags,
-                          backgroundclose=backgroundclose,
-                          **kwargs)
+        return self._repo.wwrite(self._path, data, flags,
+                                 backgroundclose=backgroundclose,
+                                 **kwargs)
 
     def markcopied(self, src):
         """marks this file a copy of `src`"""