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
os = <unloaded module 'os'>
os.system = <built-in function system>
os = <module 'os' from '?'>
util = <unloaded module 'util'>
util.system = <function system at 0x?>
util = <module 'mercurial.util' from '?'>
util.system = <function system at 0x?>
hgweb = <unloaded module 'hgweb'>
hgweb_mod = <unloaded module 'hgweb_mod'>
hgweb = <module 'mercurial.hgweb' from '?'>
fred = <unloaded module 're'>
remod = <unloaded module 're'>
re = <unloaded module 'sys'>
fred = <unloaded module 're'>
fred.sub = <function sub at 0x?>
fred = <proxied module 're'>
remod = <module 're' from '?'>
re = <unloaded module 'sys'>
re.stderr = <open file '<whatever>', mode 'w' at 0x?>
re = <proxied module 'sys'>
pvecproxy = <unloaded module 'pvec'>
pvecproxy.__doc__ = 'A "pvec" is ...'
pvecproxy.__name__ = 'mercurial.pvec'
pvecproxy.__dict__['__name__'] = 'mercurial.pvec'
pvecproxy = <proxied module 'pvec'>
contextlib = <unloaded module 'contextlib'>
contextlib.unknownattr = ImportError: cannot import name unknownattr
__import__('contextlib', ..., ['unknownattr']) = <module 'contextlib' from '?'>
hasattr(contextlibimp, 'unknownattr') = False
node = <module 'mercurial.node' from '?'>