[MERGE] Add helper class versionedfile.VersionedFilesDecorator for use with RemoteRepository in future.

[John Arbash Meinel]

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Robert Collins wrote:
> As NEWS says, a helpful generic VersionedFilesDecorator; Andrew and I
> intend to use this to avoid calls to 'start_commit_group' on
> RemoteRepository having to call _ensure_real until actual operations are
> undertaken.
> 
> -Rob
> 
> 

So IIRC, the idea is that you'll create one of this and *not* have
populated the _backing_vf yet. And then once a call is made, to
"repository.texts" (for example) it will call _ensure_real and then
populate _backing_vf and respond.

I'm a bit curious why you pass all the parameters to _hook_call, rather
than just alerting it that it is being called?

Also, why not use the __getattr__ pattern rather than having to proxy
each function?

If you are doing it this way, is there a way to hook it into the generic
tests, so that we are sure if we add a new VF api, that it also gets
implemented here?

I'm a little concerned about the overhead of calling _hook_call for
every action, though the only one we do a lot is get_parent_map. And
then it should be hundreds and not thousands (though on Emacs, it could
potentially be 80k or so). Probably it is ok.


+class RecordingVersionedFilesDecorator(VersionedFilesDecorator):
     """A minimal versioned files that records calls made on it.
 ...

Instead of passing a function to VFD.__init__ you create an explicit
'def _hook_call' function. I think it would be better as:

def _rvf_hook_call(self):
  ...

def __init__(self):
  VFD.__init__(self, hook_call=self._rvf_hook_call)

Or some permutation on that.

I realize what you do *works*, but only as long as you don't call
super().__init__, which doesn't seem like a good policy to require. At a
minimum it needs to be documented in __init__. I would prefer if you
passed the hook_call parameter.

BB:tweak

John
=:->
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