Fix semantics of 'minibuffer' frame parameter

The 'minibuffer' frame parameter is now t for a normal frame
(a frame with a root window plus a minibuffer window) and the
frame's minibuffer window for a minibuffer-less frame (a frame
whose minibuffer window is on another frame).  See also:
https://lists.gnu.org/archive/html/emacs-devel/2016-07/msg01259.html

* src/frame.c (make_frame, make_frame_without_minibuffer)
(make_minibuffer_frame): When assigning the frame's minibuffer
window also store corresponding 'minibuffer' frame parameter.
(store_frame_param): Move the 'minibuffer' parameter checks to
the beginning so we can silently override the value before it
gets stored in the parameter alist.  Fix error handling.
(Fframe_parameters): Return value of 'minibuffer' parameter
unmodified.

* lisp/frameset.el (frameset-filter-minibuffer): When the cdr of
the parameter is a minibuffer window, save (minibuffer . nil)
instead of (minibuffer . t).
(frameset--reuse-frame): To find a non-minibuffer-only frame
look out for a frame whose 'minibuffer' parameter is t instead
of that frame's minibuffer window.
(frameset-minibufferless-first-p): To find a minibuffer-less
frame look out for a frame whose 'minibuffer' parameter is a
window instead of nil.

lisp/frameset.el

@@ -572,7 +572,7 @@ see `frameset-filter-alist'."
 (defun frameset-filter-minibuffer (current filtered _parameters saving)
   "Force the minibuffer parameter to have a sensible value.
 
-When saving, convert (minibuffer . #<window>) to (minibuffer . t).
+When saving, convert (minibuffer . #<window>) to (minibuffer . nil).
 When restoring, if there are two copies, keep the one pointing to
 a live window.
 
@@ -580,7 +580,12 @@ For the meaning of CURRENT, FILTERED, PARAMETERS and SAVING,
 see `frameset-filter-alist'."
   (let ((value (cdr current)) mini)
     (cond (saving
-	   (if (windowp value) '(minibuffer . t) t))
+           ;; "Fix semantics of 'minibuffer' frame parameter" change:
+           ;; When the cdr of the parameter is a minibuffer window, save
+           ;; (minibuffer . nil) instead of (minibuffer . t).
+           (if (windowp value)
+               '(minibuffer . nil)
+             t))
 	  ((setq mini (assq 'minibuffer filtered))
 	   (when (windowp value) (setcdr mini value))
 	   nil)
@@ -906,12 +911,12 @@ is the parameter alist of the frame being restored.  Internal use only."
 	   ;; If it has not been loaded, and it is not a minibuffer-only frame,
 	   ;; let's look for an existing non-minibuffer-only frame to reuse.
 	   (unless (or frame (eq (cdr (assq 'minibuffer parameters)) 'only))
+           ;; "Fix semantics of 'minibuffer' frame parameter" change:
+           ;; The 'minibuffer' frame parameter of a non-minibuffer-only
+           ;; frame is t instead of that frame's minibuffer window.
 	     (setq frame (frameset--find-frame-if
 			  (lambda (f)
-			    (let ((w (frame-parameter f 'minibuffer)))
-			      (and (window-live-p w)
-				   (window-minibuffer-p w)
-				   (eq (window-frame w) f))))
+			    (eq (frame-parameter f 'minibuffer) t))
 			  display))))
 	  (mini
 	   ;; For minibufferless frames, check whether they already exist,
@@ -1027,8 +1032,11 @@ For the meaning of FORCE-DISPLAY, see `frameset-restore'."
 	(t (not force-display))))
 
 (defun frameset-minibufferless-first-p (frame1 _frame2)
-  "Predicate to sort minibufferless frames before other frames."
-  (not (frame-parameter frame1 'minibuffer)))
+  "Predicate to sort minibuffer-less frames before other frames."
+  ;; "Fix semantics of 'minibuffer' frame parameter" change: The
+  ;; 'minibuffer' frame parameter of a minibuffer-less frame is that
+  ;; frame's minibuffer window instead of nil.
+  (windowp (frame-parameter frame1 'minibuffer)))
 
 ;;;###autoload
 (cl-defun frameset-restore (frameset

src/frame.c

@@ -658,6 +658,7 @@ make_frame (bool mini_p)
       mw->mini = 1;
       wset_frame (mw, frame);
       fset_minibuffer_window (f, mini_window);
+      store_frame_param (f, Qminibuffer, Qt);
     }
   else
     {
@@ -770,6 +771,7 @@ make_frame_without_minibuffer (Lisp_Object mini_window, KBOARD *kb,
     }
 
   fset_minibuffer_window (f, mini_window);
+  store_frame_param (f, Qminibuffer, mini_window);
 
   /* Make the chosen minibuffer window display the proper minibuffer,
      unless it is already showing a minibuffer.  */
@@ -807,6 +809,7 @@ make_minibuffer_frame (void)
 
   mini_window = f->root_window;
   fset_minibuffer_window (f, mini_window);
+  store_frame_param (f, Qminibuffer, Qonly);
   XWINDOW (mini_window)->mini = 1;
   wset_next (XWINDOW (mini_window), Qnil);
   wset_prev (XWINDOW (mini_window), Qnil);
@@ -2404,6 +2407,46 @@ store_frame_param (struct frame *f, Lisp_Object prop, Lisp_Object val)
 {
   register Lisp_Object old_alist_elt;
 
+  if (EQ (prop, Qminibuffer))
+    {
+      if (WINDOWP (val))
+	{
+	  if (!MINI_WINDOW_P (XWINDOW (val)))
+	    error ("The 'minibuffer' parameter does not specify a valid minibuffer window");
+	  else if (FRAME_MINIBUF_ONLY_P (f))
+	    {
+	      if (EQ (val, FRAME_MINIBUF_WINDOW (f)))
+		val = Qonly;
+	      else
+		error ("Can't change the minibuffer window of a minibuffer-only frame");
+	    }
+	  else if (FRAME_HAS_MINIBUF_P (f))
+	    {
+	      if (EQ (val, FRAME_MINIBUF_WINDOW (f)))
+		val = Qt;
+	      else
+		error ("Can't change the minibuffer window of a frame with its own minibuffer");
+	    }
+	  else
+	    /* Store the chosen minibuffer window.  */
+	    fset_minibuffer_window (f, val);
+	}
+      else
+	{
+	  Lisp_Object old_val = Fcdr (Fassq (Qminibuffer, f->param_alist));
+
+	  if (!NILP (old_val))
+	    {
+	      if (WINDOWP (old_val) && NILP (val))
+		/* Don't change the value for a minibuffer-less frame if
+		   only nil was specified as new value.  */
+		val = old_val;
+	      else if (!EQ (old_val, val))
+		error ("Can't change the 'minibuffer' parameter of this frame");
+	    }
+	}
+    }
+
   /* The buffer-list parameters are stored in a special place and not
      in the alist.  All buffers must be live.  */
   if (EQ (prop, Qbuffer_list))
@@ -2475,19 +2518,6 @@ store_frame_param (struct frame *f, Lisp_Object prop, Lisp_Object val)
       else if (EQ (prop, Qname))
 	set_term_frame_name (f, val);
     }
-
-  if (EQ (prop, Qminibuffer) && WINDOWP (val))
-    {
-      if (! MINI_WINDOW_P (XWINDOW (val)))
-	error ("Surrogate minibuffer windows must be minibuffer windows");
-
-      if ((FRAME_HAS_MINIBUF_P (f) || FRAME_MINIBUF_ONLY_P (f))
-	  && !EQ (val, f->minibuffer_window))
-	error ("Can't change the surrogate minibuffer of a frame with its own minibuffer");
-
-      /* Install the chosen minibuffer window, with proper buffer.  */
-      fset_minibuffer_window (f, val);
-    }
 }
 
 /* Return color matches UNSPEC on frame F or nil if UNSPEC
@@ -2565,10 +2595,6 @@ If FRAME is omitted or nil, return information on the currently selected frame.
 	   : FRAME_COLS (f));
   store_in_alist (&alist, Qwidth, make_number (width));
   store_in_alist (&alist, Qmodeline, (FRAME_WANTS_MODELINE_P (f) ? Qt : Qnil));
-  store_in_alist (&alist, Qminibuffer,
-		  (! FRAME_HAS_MINIBUF_P (f) ? Qnil
-		   : FRAME_MINIBUF_ONLY_P (f) ? Qonly
-		   : FRAME_MINIBUF_WINDOW (f)));
   store_in_alist (&alist, Qunsplittable, (FRAME_NO_SPLIT_P (f) ? Qt : Qnil));
   store_in_alist (&alist, Qbuffer_list, f->buffer_list);
   store_in_alist (&alist, Qburied_buffer_list, f->buried_buffer_list);