2015-07-22 Martin Rudalics <rudalics@gmx.at>

Optionally even widths of `display-buffer' windows.  (Bug#21100)

* lisp/window.el (quit-restore-window): Restore width if
requested.
(display-buffer-record-window): Record width when window is
reused and horizontally combined.
(even-window-sizes): New option to allow evening window widths.
(even-window-heights): Defalias to `even-window-sizes'.
(window--even-window-heights): Rename to
`window--even-window-sizes'.  Handle side-by-side windows.
(display-buffer-use-some-window): Call `window--even-window-sizes'
instead of `window--even-window-heights'.
* lisp/help.el (resize-temp-buffer-window): Fix indentation.

* doc/lispref/windows.texi (Choosing Window Options): Describe
`even-window-sizes'.
(Coordinates and Windows): Fix typo.

doc/lispref/windows.texi

@@ -2547,6 +2547,21 @@ least that many columns.  If the value is @code{nil}, that means not
 to split this way.
 @end defopt
 
+@defopt even-window-sizes
+This variable, if non-nil, causes @code{display-buffer} to even window
+sizes whenever it reuses an existing window and that window is adjacent
+to the selected one.
+
+If its value is @code{width-only}, sizes are evened only if the reused
+window is on the left or right of the selected one and the selected
+window is wider than the reused one.  If its value is @code{height-only}
+sizes are evened only if the reused window is above or beneath the
+selected window and the selected window is higher than the reused one.
+Any other non-@code{nil} value means to even sizes in any of these cases
+provided the selected window is larger than the reused one in the sense
+of their combination.
+@end defopt
+
 @defopt pop-up-frames
 If the value of this variable is non-@code{nil}, that means
 @code{display-buffer} may display buffers by making new frames.  The
@@ -3690,7 +3705,7 @@ The coordinates are in the header line of @var{window}.
 The coordinates are in the divider separating @var{window} from a
 window on the right.
 
-@item right-divider
+@item bottom-divider
 The coordinates are in the divider separating @var{window} from a
 window beneath.
 

etc/NEWS

@@ -1106,6 +1106,10 @@ and `window-divider-default-right-width'.
 how `switch-to-buffer' proceeds interactively when the selected window
 is strongly dedicated to its buffer.
 
++++
+** The option `even-window-heights' has been renamed to
+`even-window-sizes' and now handles window widths as well.
+
 ** Tearoff menus and detachable toolbars for Gtk+ has been removed.
 Those features have been deprecated in Gtk+ for a long time.
 

lisp/help.el

@@ -1163,8 +1163,8 @@ size of WINDOW."
 		       (and (window-combined-p window t)
 			    fit-window-to-buffer-horizontally)))
 	      (and (eq quit-cadr 'frame)
-		     fit-frame-to-buffer
-		     (eq window (frame-root-window window))))
+                   fit-frame-to-buffer
+                   (eq window (frame-root-window window))))
 	(fit-window-to-buffer window height nil width nil t))))
 
 ;;; Help windows.

lisp/window.el

@@ -4358,11 +4358,18 @@ nil means to not handle the buffer in a particular way.  This
 	   (eq (nth 3 quit-restore) buffer))
       ;; Show another buffer stored in quit-restore parameter.
       (when (and (integerp (nth 3 quad))
-		 (/= (nth 3 quad) (window-total-height window)))
+		 (if (window-combined-p window)
+                     (/= (nth 3 quad) (window-total-height window))
+                   (/= (nth 3 quad) (window-total-width window))))
 	;; Try to resize WINDOW to its old height but don't signal an
 	;; error.
 	(condition-case nil
-	    (window-resize window (- (nth 3 quad) (window-total-height window)))
+	    (window-resize
+             window
+             (- (nth 3 quad) (if (window-combined-p window)
+                                 (window-total-height window)
+                               (window-total-width window)))
+             (window-combined-p window t))
 	  (error nil)))
       (set-window-dedicated-p window nil)
       ;; Restore WINDOW's previous buffer, start and point position.
@@ -5500,7 +5507,9 @@ element is BUFFER."
 		     ;; Preserve window-point-insertion-type (Bug#12588).
 		     (copy-marker
 		      (window-point window) window-point-insertion-type)
-		     (window-total-height window))
+		     (if (window-combined-p window)
+                         (window-total-height window)
+                       (window-total-width window)))
 	       (selected-window) buffer)))))
    ((eq type 'window)
     ;; WINDOW has been created on an existing frame.
@@ -6081,33 +6090,38 @@ represents a live window, nil otherwise."
                        ))
 	frame))))
 
-(defcustom even-window-heights t
-  "If non-nil `display-buffer' will try to even window heights.
+(defcustom even-window-sizes t
+  "If non-nil `display-buffer' will try to even window sizes.
 Otherwise `display-buffer' will leave the window configuration
-alone.  Heights are evened only when `display-buffer' chooses a
-window that appears above or below the selected window."
+alone.  Special values are `height-only' to even heights only and
+`width-only' to even widths only.  Any other value means to even
+any of them."
   :type 'boolean
   :group 'windows)
+(defvaralias 'even-window-heights 'even-window-sizes)
 
-(defun window--even-window-heights (window)
-  "Even heights of WINDOW and selected window.
-Do this only if these windows are vertically adjacent to each
-other, `even-window-heights' is non-nil, and the selected window
-is higher than WINDOW."
-  (when (and even-window-heights
-	     ;; Even iff WINDOW forms a vertical combination with the
-	     ;; selected window, and WINDOW's height exceeds that of the
-	     ;; selected window, see also bug#11880.
-	     (window-combined-p window)
-	     (= (window-child-count (window-parent window)) 2)
-	     (eq (window-parent) (window-parent window))
-	     (> (window-total-height) (window-total-height window)))
-    ;; Don't throw an error if we can't even window heights for
-    ;; whatever reason.
-    (condition-case nil
-	(enlarge-window
-	 (/ (- (window-total-height window) (window-total-height)) 2))
-      (error nil))))
+(defun window--even-window-sizes (window)
+  "Even sizes of WINDOW and selected window.
+Even only if these windows are the only children of their parent,
+`even-window-sizes' has the appropriate value and the selected
+window is larger than WINDOW."
+  (when (and (= (window-child-count (window-parent window)) 2)
+             (eq (window-parent) (window-parent window)))
+    (cond
+     ((and (not (memq even-window-sizes '(nil height-only)))
+           (window-combined-p window t)
+           (> (window-total-width) (window-total-width window)))
+      (condition-case nil
+          (enlarge-window
+           (/ (- (window-total-width window) (window-total-width)) 2) t)
+        (error nil)))
+     ((and (not (memq even-window-sizes '(nil width-only)))
+           (window-combined-p window)
+           (> (window-total-height) (window-total-height window)))
+      (condition-case nil
+          (enlarge-window
+           (/ (- (window-total-height window) (window-total-height)) 2))
+        (error nil))))))
 
 (defun window--display-buffer (buffer window type &optional alist dedicated)
   "Display BUFFER in WINDOW.
@@ -6767,7 +6781,7 @@ that frame."
 
       (prog1
 	  (window--display-buffer buffer window 'reuse alist)
-	(window--even-window-heights window)
+	(window--even-window-sizes window)
 	(unless (cdr (assq 'inhibit-switch-frame alist))
 	  (window--maybe-raise-frame (window-frame window)))))))