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

From: Stefan Monnier <[email-masked]>
Date: Tue, 19 Mar 2013 23:12:08 -0400

>> 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.).

It only does one half: change a few callers to handle a non-window
return value.  But the other half is important: the non-window return
value should only be possible if the caller announces that it's ready to
handle it.

        Stefan

> 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.