Re: display-buffer-alist simplifications

[martin rudalics]

> In defface specs parameters like `min-width 10' are specified in the
> condition part of `defface' like `min-colors 88' as a list.
> For non-conditional parameters I agree that the plist syntax is better.
> And defface spec merges plist attributes from inherited faces.

Sorry.  I'm a bit lost here.  Is this what is done in the filter parts
of this form

    (:inherit
     (repeat :tag "Inherit"

in `custom-face-attributes'?  If so, then this specifies inheritance
explicitly.  The inheritance mechanism used by `display-buffer-alist' is
implicit.

Let's consider the following example setup:

(setq
 display-buffer-alist
 '((((regexp . ".*")) (pop-up-window (largest) (lru)))
   (((regexp . "^\\*Help\\*$")) (pop-up-window-set-height . 
fit-window-to-buffer))
   (((regexp . "^\\*.+\\*$")) (pop-up-window-set-height . 20))
   (((regexp . ".*")) (pop-up-window-min-height . 15))))

This currently means that a user wants to

(1) Pop up a window for any buffer either below the largest or least
    recently used window.  The minimum height is 15 lines; if Emacs
    can't make a window that large, don't bother popping up a window.

(2) For "*...*" buffers try setting the window height to 20 lines.  If
    this is not possible, leave the height alone.

(3) For *Help* buffers try fitting the window to the height of the
    buffer.

So the minimum height of the popped up window is inherited for all
"*...*" buffers.

Now the questions are whether (1) writing such specifications is useful
in the first place, and (2) whether such implicit inheritance is useful.
If they are, I don't see a way to _explicitly_ specify that *Help*
buffers should inherit the minimum window height from the specifier for
all buffers.

> I also want to note that tags like `reuse-window' and `pop-up-window'
> are redundant in plists.  Their meaning can be expressed as plists like
> `:window same', `:window other', `:buffer same'.

These tags are mainly used to group items together for the customization
interface: A user caring about how to display a buffer on a separate
frame shouldn't be concerned with specifiers that describe how to pop up
a new window for that buffer.  On the "top level" :window is ambiguous
because it can mean the window to reuse or the window to split.  So we
would have to write ":window-to-reuse same" and ":window-to-split lru"
or something the like.

> This would bring
> them closer to the syntax of defface specs that is proven to be flexible
> and easy to configure.

If I leave in inheritance, the form above could be simplified to say

(setq
 display-buffer-alist
 '((".*" :pop-up-window largest)
   (".*" :pop-up-window lru)
   ("^\\*Help\\*$" :pop-up-window-set-height fit-window-to-buffer)
   ("^\\*.+\\*$" :pop-up-window-set-height 20)
   (".*" :pop-up-window-min-height 15)))

If we don't want inheritance, we'd probably have to write a thing like

(setq
 display-buffer-alist
 '(("^\\*Help\\*$"
    :pop-up-window largest
    :pop-up-window-set-height fit-window-to-buffer
    :pop-up-window-min-height 15)
   ("^\\*Help\\*$"
    :pop-up-window lru
    :pop-up-window-set-height fit-window-to-buffer
    :pop-up-window-min-height 15)
   ("^\\*.+\\*$"
    :pop-up-window largest
    :pop-up-window-set-height 20
    :pop-up-window-min-height 15)
   ("^\\*.+\\*$"
    :pop-up-window lru
    :pop-up-window-set-height 20
    :pop-up-window-min-height 15)
   (".*"
    :pop-up-window largest
    :pop-up-window-min-height 15)
   ("^\\*.+\\*$"
    :pop-up-window lru
    :pop-up-window-min-height 15)))

instead.

martin