[PATCH 12 of 14] vfs: add the possibility to have a "ward" to check vfs usage

[Yuya Nishihara]

On Sun, 02 Jul 2017 04:56:37 +0200, Pierre-Yves David wrote:
> # HG changeset patch
> # User Pierre-Yves David <pierre-yves.david at ens-lyon.org>
> # Date 1470323266 -7200
> #      Thu Aug 04 17:07:46 2016 +0200
> # Node ID ebf81efdd6d7ff15c64683933635616c00475688
> # Parent  34b8be7f0420b07d0f7b71379c6055e5b26223d5
> # EXP-Topic vfs.ward
> # Available At https://www.mercurial-scm.org/repo/users/marmoute/mercurial/
> #              hg pull https://www.mercurial-scm.org/repo/users/marmoute/mercurial/ -r ebf81efdd6d7
> vfs: add the possibility to have a "ward" to check vfs usage

> The feature has some similarity with the 'pathauditor', but further digging
> show it make more sense to keep them separated. The path auditor is fairly
> autonomous (create from vfs.__init__ without any extra information), and check
> very generic details. On the other hand, the wards will have deeper knownledge
> of the Mercurial logic and is created at the local repository level. Mixing the
> two would add much complexity for no real gains.

My gut feeling is that vfs isn't the right place if they require deeper
knowledge of repository/dirstate logic. And the whole weakref business
floating around wards, hooks and transaction seems like just getting around
layering violation.

> We currently only apply the ward on 'open' operation. We will extend this to
> other operations like copy, creation and removal later. The current readonlyvfs
> seems to have the same shortcoming.
> 
> diff --git a/mercurial/vfs.py b/mercurial/vfs.py
> --- a/mercurial/vfs.py
> +++ b/mercurial/vfs.py
> @@ -284,7 +284,7 @@ class vfs(abstractvfs):
>      This class is used to hide the details of COW semantics and
>      remote file access from higher level code.
>      '''
> -    def __init__(self, base, expandpath=False, realpath=False):
> +    def __init__(self, base, expandpath=False, realpath=False, ward=None):
>          if expandpath:
>              base = util.expandpath(base)
>          if realpath:
> @@ -293,6 +293,11 @@ class vfs(abstractvfs):
>          self.audit = pathutil.pathauditor(self.base)
>          self.createmode = None
>          self._trustnlink = None
> +        # optional function to validate operation on file
> +        # intended to be user for developer checks.
> +        #
> +        # XXX should be call for other things than 'open'
> +        self._ward = ward
>  
>      @util.propertycache
>      def _cansymlink(self):
> @@ -343,6 +348,9 @@ class vfs(abstractvfs):
>          if not text and "b" not in mode:
>              mode += "b" # for that other OS
>  
> +        if self._ward is not None:
> +            self._ward(f, mode, atomictemp)

Do you have any idea how to expand this ward() callback to the other vfs
operations, which have different set of parameters?