Subject: Re: bug#13594: 24.2.92; [PATCH] compilation-start doesn't consider nil OUTWIN

From: Leo Liu <[email-masked]>
Date: Tue, 19 Mar 2013 23:39:54 +0800

On 2013-02-14 22:15 +0800, Stefan Monnier wrote:
> Basically, as it currently stands "don't display at all" can be done in
> 2 ways:
> - make it work only for those callers that are prepared for it: for this
>   case, we could simply define a t return value (returned from an
>   ACTION) to mean "not displayed".  Ideally, display-buffer would return
>   nil in this case, but returning t is OK as well.
> - make it work everywhere: then we need display-buffer to return
>   a "dummy" window (i.e. an object that behaves like a window object
>   but that is not displayed).
>
> I'm beginning to think the best choice is the first option: it requires
> no changes right away, and we can progressively change callers so that
> they can handle the "not displayed" case.

Does this roughly follow your idea? i.e. document display-buffer to
allow non-window return value (I also get rid of mentioning nil). In
compile.el, handle non-window return value. The attached patch does
these two. (I'll prepare a thorough patch tomorrow.).

diff --git a/lisp/progmodes/compile.el b/lisp/progmodes/compile.el
index b82afc67..8edfe487 100644
--- a/lisp/progmodes/compile.el
+++ b/lisp/progmodes/compile.el
@@ -1638,7 +1638,8 @@ (defun compilation-start (command &optional mode name-function highlight-regexp)
 	     (list command mode name-function highlight-regexp))
 	(set (make-local-variable 'revert-buffer-function)
 	     'compilation-revert-buffer)
-	(set-window-start outwin (point-min))
+	(when (windowp outwin)
+	  (set-window-start outwin (point-min)))
 
 	;; Position point as the user will see it.
 	(let ((desired-visible-point
@@ -1647,15 +1648,18 @@ (defun compilation-start (command &optional mode name-function highlight-regexp)
 		   (point-max)
 		 ;; Normally put it at the top.
 		 (point-min))))
-	  (if (eq outwin (selected-window))
-	      (goto-char desired-visible-point)
-	    (set-window-point outwin desired-visible-point)))
+	  (cond
+	   ((windowp outwin)
+	    (set-window-point outwin desired-visible-point))
+	   ((eq outwin (selected-window))
+	    (goto-char desired-visible-point))))
 
 	;; The setup function is called before compilation-set-window-height
 	;; so it can set the compilation-window-height buffer locally.
 	(if compilation-process-setup-function
 	    (funcall compilation-process-setup-function))
-	(compilation-set-window-height outwin)
+	(and (windowp outwin)
+	     (compilation-set-window-height outwin))
 	;; Start the compilation.
 	(if (fboundp 'start-process)
 	    (let ((proc
diff --git a/lisp/window.el b/lisp/window.el
index 63d75f60..e96c8c60 100644
--- a/lisp/window.el
+++ b/lisp/window.el
@@ -5368,7 +5368,8 @@ (defun display-buffer (buffer-or-name &optional action frame)
   "Display BUFFER-OR-NAME in some window, without selecting it.
 BUFFER-OR-NAME must be a buffer or the name of an existing
 buffer.  Return the window chosen for displaying BUFFER-OR-NAME,
-or nil if no such window is found.
+or a non-nil value to mean one of the actions forbids displaying
+the buffer.
 
 Optional argument ACTION, if non-nil, should specify a display
 action.  Its form is described below.
@@ -5394,7 +5395,9 @@ (defun display-buffer (buffer-or-name &optional action frame)
 `display-buffer-fallback-action' (in order).  Then it calls each
 function in the combined function list in turn, passing the
 buffer as the first argument and the combined alist as the second
-argument, until one of the functions returns non-nil.
+argument, until one of the functions returns non-nil.  If the
+value is not a window object, the search stops and no buffer is
+displayed.
 
 If ACTION is nil, the function list and the alist are built using
 only the other variables mentioned above.