[PATCH 4 of 8] transaction: avoid file stat ambiguity only for files in blacklist

[Yuya Nishihara]

On Fri, 30 Jun 2017 01:53:11 +0900, FUJIWARA Katsunori wrote:
> # HG changeset patch
> # User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
> # Date 1498754869 -32400
> #      Fri Jun 30 01:47:49 2017 +0900
> # Node ID d4d47784511456e6cf77b194822f23586e052312
> # Parent  9114ae36f40b733912705ef0bacb2961941f18d6
> transaction: avoid file stat ambiguity only for files in blacklist

> diff --git a/mercurial/transaction.py b/mercurial/transaction.py
> --- a/mercurial/transaction.py
> +++ b/mercurial/transaction.py
> @@ -44,11 +44,12 @@ def active(func):
>      return _active
>  
>  def _playback(journal, report, opener, vfsmap, entries, backupentries,
> -              unlink=True):
> +              unlink=True, noambigstatfiles=None):
>      for f, o, _ignore in entries:
>          if o or not unlink:
> +            checkambig = noambigstatfiles and (f, '') in noambigstatfiles
>              try:
> -                fp = opener(f, 'a', checkambig=True)
> +                fp = opener(f, 'a', checkambig=checkambig)
>                  fp.truncate(o)
>                  fp.close()
>              except IOError:
> @@ -101,7 +102,8 @@ def _playback(journal, report, opener, v
>  
>  class transaction(object):
>      def __init__(self, report, opener, vfsmap, journalname, undoname=None,
> -                 after=None, createmode=None, validator=None, releasefn=None):
> +                 after=None, createmode=None, validator=None, releasefn=None,
> +                 noambigstatfiles=None):
>          """Begin a new transaction
>  
>          Begins a new transaction that allows rolling back writes in the event of
> @@ -110,6 +112,10 @@ class transaction(object):
>          * `after`: called after the transaction has been committed
>          * `createmode`: the mode of the journal file that will be created
>          * `releasefn`: called after releasing (with transaction and result)
> +
> +        `noambigstatfiles` is a set of (path, vfs-location) tuples,
> +        which determine whether file stat ambiguity should be avoided
> +        for corresponded files.

IIUC, this is a set of files that could get ambiguous, but "noambig" semed to
say the opposite.

Other than that, the code looks fine. FWIW, I'm getting a feeling that we've
failed to design a sensible cache-validation API because it's quite hard to
rely only on mtime/ctime.