bug#7381: 24.0.50; Provide a hook run when a window is selected

[martin rudalics <rudalics@gmx.at>]

 > But I really don't think extending `w-c-c-hook' is the right
 > solution. I don't see why just selecting another window should be
 > considered a window configuration change...

Agreed.

 >> Basically, we could keep the old window configuration around from one
 >> "change" to the next but it's not clear whether we want to save the
 >> configuration before the last command or before the last configuration
 >> change.  In the latter case, your code would hardly know whether it runs
 >> within one and the same command or within different commands.
 >>
 >> Note in this context that a single command like setting up a GDB frame
 >> may entail a couple of configuration changes and you would have to keep
 >> track of all of them.  And the hook would trigger within each and every
 >> instance of `with-selected-window' or `save-window-excursion' no matter
 >> how silly these macros are occasionally used.
 >
 > ...and these caveats seem only to confirm such doubts (although some of
 > them would apply to lesser extent to the hypothetical
 > `select-window'-specific hook as well).

I'm afraid they would apply to the same extent.

 > What's wrong with a separate `window-selected-hook' or perhaps
 > `select-window-hook'?

Nothing but the fact that it might not help you very much.  Your use
case was formulated in terms of commands

 > ... repeating the command would toggle between two windows ...

and not in terms of window selections.  So I don't think that Lennart's
proposal of using a `post-command-hook' here is unreasonable ;-)

 > [On a related note, it would be nice if there were some clean and simple
 > way to define custom hooks attached to arbitrary functions; that would
 > solve problems similar to this one, preventing discussions whether adding
 > yet another hook is worth it or not. Something like:
 >
 >   (define-function-hook 'select-window)
 >   => select-window-hook
 >
 >   (add-hook 'select-window-hook ...)
 >
 > Dream on...]

Hooks can be dangerous.  It's very easy to crash Emacs by putting some
innocuously looking function on `window-configuration-change-hook'.

BTW, I could give `get-mru-window' an additional argument like

(defun get-mru-window (&optional all-frames avoid-selected)
    (let (best-window best-time time)
     (dolist (window (window-list-1 nil nil all-frames))
       (setq time (window-use-time window))
       (unless (and avoid-selected
		   (eq (window (selected-window))))
	(when (or (not best-time) (> time best-time))
	  (setq best-time time)
	  (setq best-window window))))
     best-window))

which would return nil if the selected window is the only one on
ALL-FRAMES.

martin