bug#18009: 24.4.50; Add hooks for `rename-file' and `delete-file'

[Drew Adams <drew.adams@oracle.com>]

> > Please add a hook for each of these basic operations.  It is not
> > unusual to want to be able to carry out some action associated with
> > (successfully) renaming or deleting a file.  The hooks would be run
> > at the end of the operation, and only upon success.
> 
> It's not unreasonable, but these are rather low-level operations, I'm
> not sure I want to run hooks from them.

I'm curious what difference that makes.  I suppose you're thinking that
if a hook does something awful then it could affect things widely.  Is
that it?

I guess I don't have a good counter argument, if so.  On the other
hand, the same thing would happen if someone advised the function.

Plus, there are hooks and there are hooks.  Some hooks have more
potential for wreaking havoc than others.  We have not created hooks
only for contexts that are benign or well isolated.  We have hooks
that, if abused, can lead to data corruption or loss.  I don't really
see why these hooks would be so different.

> > One use case: Bookmark+ autofile bookmarks have the same name as their
> > files.  (There can be multiple bookmarks with the same name,
> > corresponding to files with the same name in different directories.)
> > With a hook it would be trivial to automatically rename or delete the
> > associated bookmark.
> 
> Of course you can use an `advice' in the mean time, but maybe a better
> long-term answer is the file-notification API so that your code would
> know about renames not only when they're performed from the same Emacs
> session but also from any other process.

I will take a look at that; I'm not familiar with it.  The doc speaks
of a few restrictions and caveats, but it does sound worth trying.

Why did you mention "long-term" here? I wonder if I'm missing something.

That might well be something interesting for the use case I mentioned.
But I would still like to see the hooks added.  It is not the same
thing to want Emacs to do something when IT renames or deletes a file,
as opposed to hearing back from the operating system (when, exactly?)
that something was changed.  Associating an action with the act of
renaming or deleting makes sense to me, a priori.