[PATCH 5 of 5] util: make copyfile avoid ambiguity of file stat if needed

[Augie Fackler]

On Thu, May 19, 2016 at 12:26:31AM +0900, FUJIWARA Katsunori wrote:
> # HG changeset patch
> # User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
> # Date 1463584838 -32400
> #      Thu May 19 00:20:38 2016 +0900
> # Node ID 2767843f27d7a68a8b19bef9f8321c25215242b0
> # Parent  a74b90602bdeb11bab9cef36283f5119c96c6656
> util: make copyfile avoid ambiguity of file stat if needed

These are queued, thanks

>
> In some cases below, copying from backup is used to restore original
> contents of a file. If copying keeps ctime, mtime and size of a file,
> restoring is overlooked, and old contents cached before restoring
> isn't invalidated as expected.
>
>   - failure of transaction before closing (from '.hg/journal.backup.*')
>   - rollback of previous transaction (from '.hg/undo.backup.*')
>
> To avoid such problem, this patch makes copyfile() avoid ambiguity of
> file stat, if needed.
>
> Ambiguity check is executed, only if:
>
>   - checkambig=True is specified (not all copying needs ambiguity check), and
>   - destination file exists before copying
>
> This patch also adds 'not (copystat and checkambig)' assertion,
> because combination of copystat and checkambig is meaningless.
>
> This patch is a part of preparation for "Exact Cache Validation Plan":
>
>     https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan
>
> diff --git a/mercurial/util.py b/mercurial/util.py
> --- a/mercurial/util.py
> +++ b/mercurial/util.py
> @@ -1010,10 +1010,14 @@ def checksignature(func):
>
>      return check
>
> -def copyfile(src, dest, hardlink=False, copystat=False):
> +def copyfile(src, dest, hardlink=False, copystat=False, checkambig=False):
>      '''copy a file, preserving mode and optionally other stat info like
>      atime/mtime'''
> +    assert not (copystat and checkambig)
> +    oldstat = None
>      if os.path.lexists(dest):
> +        if checkambig:
> +            oldstat = checkambig and filestat(dest)
>          unlink(dest)
>      # hardlinks are problematic on CIFS, quietly ignore this flag
>      # until we find a way to work around it cleanly (issue4546)
> @@ -1035,6 +1039,12 @@ def copyfile(src, dest, hardlink=False,
>                  shutil.copystat(src, dest)
>              else:
>                  shutil.copymode(src, dest)
> +                if oldstat and oldstat.stat:
> +                    newstat = filestat(dest)
> +                    if newstat.isambig(oldstat):
> +                        # stat of copied file is ambiguous to original one
> +                        advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff
> +                        os.utime(dest, (advanced, advanced))
>          except shutil.Error as inst:
>              raise Abort(str(inst))
>
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