problem with uniquify.el and kill-buffer-hook

[Miles Bader]

Recently I've noticed that the `uniquify' package has stopped working
correctly, in particular, the feature controlled by the
`uniquify-after-kill-buffer-p' variable doesn't work; here's the doc:

   uniquify-after-kill-buffer-p's value is t

   If non-nil, rerationalize buffer names after a buffer has been killed.
   This can be dangerous if Emacs Lisp code is keeping track of buffers
   by their names (rather than keeping pointers to the buffers
   themselves).

I looked at the code a bit, and I think I found the problem:

This feature works by adding an appropriate local hook to
`kill-buffer-hook' in all the affected buffers.

However, this is done _before_ the buffer's mode is set (in the new
buffer that caused uniqify to be triggered); since most mode functions
call `kill-all-local-variables', this trashes the `kill-buffer-hook'.

I've found that I can fix the problem by doing:

  (put 'kill-buffer-hook 'permanent-local t)

But doing this by default may cause problems for other code (e.g., if a
particular mode adds a `kill-buffer-hook', you probably want that hook
to be deleted if the mode changes).

Since `kill-all-local-variables' first calls `change-major-mode-hook' I
guess another solution would be to make uniquify add some hair to
`change-major-mode-hook' that tries to preserve its entry in
`kill-buffer-hook' across the kill-all-local-variables', but I'm not
sure how this can be done without another hook that runs _after_
kill-all-local-variables has done its job.

Does anyone have any ideas for a solution?  The real problem here seems
to be that kill-buffer-hook can contain both mode-specific and
non-mode-specific entries; I'm not sure if any modes actually use
kill-buffer-hook though...

Also, any ideas why this just stopped working recently?  I didn't see
any _obvious_ things in the ChangeLogs, but maybe I just missed it.

Another thing (whew!), is that uniquify.el uses `defadvice' (on
`rename-buffer', and `create-file-buffer') and I wonder if it should be
changed to just have those functions invoke it directly.

Anyway sorry for the long rambling message!

Thanks,

-Miles
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