# HG changeset patch
# User Boris Feld <boris.feld@octobus.net>
# Date 1516205275 -3600
# Node ID 45b678bf3a787085d56fad5bee494e0c160aa120
# Parent  2a7e777c9eeda329a147fd10785935167617d4fb
atomicupdate: add an experimental option to use atomictemp when updating

In some cases Mercurial truncating files when updating causes problems. It can
happens when processes are currently reading the file or with big file or on
NFS mounts.

We add an experimental option to use the atomictemp option of vfs.__call__ in
order to avoid the problem.

The localrepository.wwrite seems to assume the files are created without the
`x` flag; with atomictempfile, the new file might inherit the `x` flag from
the destination. We force remove it afterward. This code could be refactored
and the flag processing could be moved inside vfs.

This patch should be tested with
`--extra-config-opt experimental.update.atomic-file=True`
as we disabled the option by default.

Differential Revision: https://phab.mercurial-scm.org/D1882

diff -r 2a7e777c9eed -r 45b678bf3a78 mercurial/configitems.py
--- a/mercurial/configitems.py	Wed Jan 17 16:52:13 2018 +0100
+++ b/mercurial/configitems.py	Wed Jan 17 17:07:55 2018 +0100
@@ -568,6 +568,9 @@
 coreconfigitem('experimental', 'treemanifest',
     default=False,
 )
+coreconfigitem('experimental', 'update.atomic-file',
+    default=False,
+)
 coreconfigitem('extensions', '.*',
     default=None,
     generic=True,
diff -r 2a7e777c9eed -r 45b678bf3a78 mercurial/localrepo.py
--- a/mercurial/localrepo.py	Wed Jan 17 16:52:13 2018 +0100
+++ b/mercurial/localrepo.py	Wed Jan 17 17:07:55 2018 +0100
@@ -1112,6 +1112,8 @@
                             **kwargs)
             if 'x' in flags:
                 self.wvfs.setflags(filename, False, True)
+            else:
+                self.wvfs.setflags(filename, False, False)
         return len(data)
 
     def wwritedata(self, filename, data):
diff -r 2a7e777c9eed -r 45b678bf3a78 mercurial/merge.py
--- a/mercurial/merge.py	Wed Jan 17 16:52:13 2018 +0100
+++ b/mercurial/merge.py	Wed Jan 17 17:07:55 2018 +0100
@@ -1376,7 +1376,9 @@
                 if repo.wvfs.lexists(absf):
                     util.rename(absf, orig)
             wctx[f].clearunknown()
-            wctx[f].write(fctx(f).data(), flags, backgroundclose=True)
+            atomictemp = ui.configbool("experimental", "update.atomic-file")
+            wctx[f].write(fctx(f).data(), flags, backgroundclose=True,
+                          atomictemp=atomictemp)
             if i == 100:
                 yield i, f
                 i = 0