window--display-buffer：如何在创建时精确设置窗口宽度

Question

With respect to the function window--display-buffer , I have been unable to precisely set the window width using a number -- eg, '((window-width . 82)) . The width is always slightly less than it should be. Any assistance to reliably use a number to set the window width would be greatly appreciated.

The documentation ( https://www.gnu.org/software/emacs/manual/html_node/elisp/Display-Action-Functions.html ) states as follows:

To adjust the window's width, use an entry whose car is window-width and whose cdr is one of:

• nil means to leave the width of the new window alone.

• A number specifies the desired width of the new window. An integer number specifies the number of columns of the window. A floating point number gives the fraction of the window's width with respect to the width of the frame's root window.

• If the cdr specifies a function , that function is called with one argument: the new window . The function is supposed to adjust the width of the window; its return value is ignored.

---

Here is a broken-example that demonstrates the problem with window--display-buffer when using a number -- eg, '((window-width . 82))

(defun broken-example ()
  (interactive)
  (window--display-buffer
   ;; buffer
   (get-buffer-create "*test*")
   ;; window
   (split-window (selected-window) nil 'right)
   ;; type
   'window
   ;; alist
   '((window-width . 82))
   ;; dedicated
   t) 
  (message "Window Width:  %s" (window-width (get-buffer-window "*test*"))) )  

---

Here is a working-example that uses the third option -- ie, a function whose argument is the new window :

(defun working-example ()
  (interactive)
  (window--display-buffer
   ;; buffer
   (get-buffer-create "*test*")
   ;; window
   (split-window (selected-window) nil 'right)
   ;; type
   'window
   ;; alist
   '((window-width . set-window-width))
   ;; dedicated
   t)
  (message "Window Width:  %s" (window-width (get-buffer-window "*test*"))) )

(defun set-window-width (window)
  "Set the selected window's width."
  (window-resize window (- 82 (window-width)) t) )

Answer 1

As to a current version of Emacs Trunk built on March 19, 2014, the following modification of line 5944 of window.el from (delta (- new-width (window-total-width window)))) to (delta (- new-width (window-width window)))) resolves this issue.

EDIT (March 22, 2014): Here is a link to the open bug report on this issue -- http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17065