bug#3142: 23.0.92; split-window-prefered-function should be able to use split-window-horizontally/split-window-vertically

[martin rudalics]

> Thanks, the only thing to fix I noticed is the missing const option for
> the default value split-window-sensibly in split-window-preferred-function.

I added the const option, rewrote some doc-strings, and narrowed the
scope of the condition-case.  If no one objects I shall commit that.

Thanks, martin

*** window.el.~1.179.~  2009-04-29 07:50:42.078125000 +0200
--- window.el   2009-05-01 17:28:24.125000000 +0200
***************
*** 794,832 ****
    :type 'boolean
    :group 'windows)
  
  (defcustom split-height-threshold 80
    "Minimum height of window to be split vertically.
! If the value is a number, `display-buffer' can split a window
! only if it has at least as many lines.  If the value is nil,
! `display-buffer' cannot split a window vertically.
! 
! If the window is the only window on its frame, `display-buffer'
! can split it regardless of this value."
    :type '(choice (const nil) (number :tag "lines"))
    :version "23.1"
    :group 'windows)
  
  (defcustom split-width-threshold 160
    "Minimum width of window to be split horizontally.
! If the value is a number, `display-buffer' can split a window
! only if it has at least as many columns.  If the value is nil,
! `display-buffer' cannot split a window horizontally."
    :type '(choice (const nil) (number :tag "columns"))
    :version "23.1"
    :group 'windows)
  
- (defcustom split-window-preferred-function nil
-   "Function used by `display-buffer' to split windows.
- If non-nil, a function called with a window as single argument
- supposed to split that window and return the new window.  If the
- function returns nil the window is not split.
- 
- If nil, `display-buffer' will split the window respecting the
- values of `split-height-threshold' and `split-width-threshold'."
-   :type '(choice (const nil) (function :tag "Function"))
-   :version "23.1"
-   :group 'windows)
- 
  (defun window--splittable-p (window &optional horizontal)
    "Return non-nil if WINDOW can be split evenly.
  Optional argument HORIZONTAL non-nil means check whether WINDOW
--- 794,848 ----
    :type 'boolean
    :group 'windows)
  
+ (defcustom split-window-preferred-function 'split-window-sensibly
+   "Function called by `display-buffer' to split a window.
+ The window that shall be split is selected when this function is
+ called.  The function is supposed to either return the new window
+ or nil if the selected window can (or shall) not be split.
+ 
+ The default is to split the window \"sensibly\".  This calls the
+ function `split-window-sensibly' which tries to split the window
+ in a way which seems most suitable.  A second standard option is
+ \"vertically\" which calls the function `split-window-vertically'
+ to split the window into two windows one above the other.  The
+ third standard option is \"horizontally\" which calls the
+ function `split-window-horizontally' to split the window into two
+ windows side by side.
+ 
+ If you set this to any other function, observe that it may be
+ called two times: A first time with the largest window selected
+ and, if that call fails to provide a suitable window, a second
+ time with the least recently used window selected.  If neither of
+ these calls produces a suitable window, `display-buffer' will use
+ an existing one to display its buffer."
+   :type '(choice
+         (const :tag "Split sensibly" split-window-sensibly)
+         (const :tag "Split vertically" split-window-vertically)
+         (const :tag "Split horizontally" split-window-horizontally)
+         (function :tag "Function"))
+   :version "23.1"
+   :group 'windows)
+ 
  (defcustom split-height-threshold 80
    "Minimum height of window to be split vertically.
! If the value is a number, `split-window-sensibly' splits a window
! vertically only if it has at least as many lines.  If the value
! is nil, it does not split a window vertically.  If a window is
! the only window on its frame, it can be split regardless of the
! value of this variable."
    :type '(choice (const nil) (number :tag "lines"))
    :version "23.1"
    :group 'windows)
  
  (defcustom split-width-threshold 160
    "Minimum width of window to be split horizontally.
! If the value is a number, `split-window-sensibly' splits a window
! only if it has at least as many columns.  If the value is nil, it
! does not split a window horizontally."
    :type '(choice (const nil) (number :tag "columns"))
    :version "23.1"
    :group 'windows)
  
  (defun window--splittable-p (window &optional horizontal)
    "Return non-nil if WINDOW can be split evenly.
  Optional argument HORIZONTAL non-nil means check whether WINDOW
***************
*** 882,911 ****
                      (* 2 (max window-min-height
                                (if mode-line-format 2 1))))))))))
  
  (defun window--try-to-split-window (window)
!   "Split WINDOW if it is splittable.
! See `window--splittable-p' for how to determine whether a window
! is splittable.  If WINDOW can be split, return the value returned
! by `split-window' (or `split-window-preferred-function')."
!   (when (and (window-live-p window)
!            (not (frame-parameter (window-frame window) 'unsplittable)))
!     (if (functionp split-window-preferred-function)
!       ;; `split-window-preferred-function' is specified, so use it.
!       (funcall split-window-preferred-function window)
!       (or (and (window--splittable-p window)
!              ;; Split window vertically.
!              (split-window window))
!         (and (window--splittable-p window t)
!              ;; Split window horizontally.
!              (split-window window nil t))
!         (and (eq window (frame-root-window (window-frame window)))
!              (not (window-minibuffer-p window))
!              ;; If WINDOW is the only window on its frame and not the
!              ;; minibuffer window, attempt to split it vertically
!              ;; disregarding the value of `split-height-threshold'.
!              (let ((split-height-threshold 0))
!                (and (window--splittable-p window)
!                     (split-window window))))))))
  
  (defun window--frame-usable-p (frame)
    "Return FRAME if it can be used to display a buffer."
--- 898,945 ----
                      (* 2 (max window-min-height
                                (if mode-line-format 2 1))))))))))
  
+ (defun split-window-sensibly ()
+   "\"Sensibly\" split the selected window.
+ If the selected window has at least `split-height-threshold'
+ lines, split it into two windows one above the other and return
+ the lower one.  Otherwise, if the selected window is at least
+ `split-width-threshold' columns wide, split it into two windows
+ side by side and return the one on the right.  If this does not
+ produce a suitable window either and the selected window is the
+ only one on its frame, try to split that window vertically and
+ return the lower one.  Return nil if that fails as well.
+ 
+ The default value of `split-window-preferred-function' is set to
+ this function."
+   (or (and (window--splittable-p (selected-window))
+          ;; Split window vertically.
+          (split-window-vertically))
+       (and (window--splittable-p (selected-window) t)
+          ;; Split window horizontally.
+          (split-window-horizontally))
+       (and (eq (selected-window) (frame-root-window))
+          (not (window-minibuffer-p))
+          ;; If the selected window is the only window on its frame and
+          ;; is not the minibuffer window, try to split it vertically
+          ;; disregarding the value of `split-height-threshold'.
+          (let ((split-height-threshold 0))
+            (and (window--splittable-p (selected-window))
+                 (split-window-vertically))))))
+ 
  (defun window--try-to-split-window (window)
!   "Split WINDOW if it can be split.
! Return value returned by `split-window-preferred-function' if it
! represents a live window, nil otherwise."
!       (and (window-live-p window)
!          (not (frame-parameter (window-frame window) 'unsplittable))
!          (with-selected-window window
!            (let ((new-window
!                   ;; Since `split-window-preferred-function' might
!                   ;; throw an error use `condition-case'.
!                   (condition-case nil
!                       (funcall split-window-preferred-function)
!                     (error nil))))
!              (and (window-live-p new-window) new-window)))))
  
  (defun window--frame-usable-p (frame)
    "Return FRAME if it can be used to display a buffer."