Subject: Re: bug#58343: 29.0.50; ELisp code run in "inconsitent" selected-window state

From: Stefan Monnier <[email-masked]>
Date: Wed, 12 Oct 2022 14:35:33 -0400

Hi Alan,

> One minor problem I see at the moment is that the call to
> move_minibuffers_onto_frame wasn't moved together with the surrounding
> code.  With its current calling convention, it needs to be called
> _after_ selected_frame has been set, because it uses selected_frame.

Aha!

> Is there any reason this function call was left where it was?

I was afraid that swapping `move_minibuffers_onto_frame` and

  if (EQ (f->selected_window, f->minibuffer_window)
      /* The following test might fail if the mini-window contains a
	 non-active minibuffer.  */
      && NILP (Fminibufferp (XWINDOW (f->minibuffer_window)->contents, Qt)))
    {
      Lisp_Object w = call1 (Qget_mru_window, frame);
      if (WINDOW_LIVE_P (w)) /* W can be nil in minibuffer-only frames.  */
        Fset_frame_selected_window (frame, w, Qnil);
    }

would not result in the same final result, e.g. because the name
"move_minibuffers_onto_frame" suggests it might change the result of
`XWINDOW (f->minibuffer_window)->contents`.

> Or could it just be moved, too?  Otherwise, its calling convention
> will need to be adapted.

The patch below refrains from moving it and passes it the to-be-selected
frame as argument instead.

        Stefan

diff --git a/src/frame.c b/src/frame.c
index 91b9bec82c3..24de0701d13 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -1503,17 +1503,7 @@ do_switch_frame (Lisp_Object frame, int for_deletion, Lisp_Object norecord)
 
   sf->select_mini_window_flag = MINI_WINDOW_P (XWINDOW (sf->selected_window));
 
-  selected_frame = frame;
-
-  move_minibuffers_onto_frame (sf, for_deletion);
-
-  if (f->select_mini_window_flag
-      && !NILP (Fminibufferp (XWINDOW (f->minibuffer_window)->contents, Qt)))
-    f->selected_window = f->minibuffer_window;
-  f->select_mini_window_flag = false;
-
-  if (! FRAME_MINIBUF_ONLY_P (XFRAME (selected_frame)))
-    last_nonminibuf_frame = XFRAME (selected_frame);
+  move_minibuffers_onto_frame (sf, frame, for_deletion);
 
   /* If the selected window in the target frame is its mini-window, we move
      to a different window, the most recently used one, unless there is a
@@ -1528,6 +1518,16 @@ do_switch_frame (Lisp_Object frame, int for_deletion, Lisp_Object norecord)
         Fset_frame_selected_window (frame, w, Qnil);
     }
 
+  selected_frame = frame;
+
+  if (f->select_mini_window_flag
+      && !NILP (Fminibufferp (XWINDOW (f->minibuffer_window)->contents, Qt)))
+    f->selected_window = f->minibuffer_window;
+  f->select_mini_window_flag = false;
+
+  if (! FRAME_MINIBUF_ONLY_P (XFRAME (selected_frame)))
+    last_nonminibuf_frame = XFRAME (selected_frame);
+
   Fselect_window (f->selected_window, norecord);
 
   /* We want to make sure that the next event generates a frame-switch
@@ -2110,7 +2110,7 @@ delete_frame (Lisp_Object frame, Lisp_Object force)
   else
     /* Ensure any minibuffers on FRAME are moved onto the selected
        frame.  */
-    move_minibuffers_onto_frame (f, true);
+    move_minibuffers_onto_frame (f, selected_frame, true);
 
   /* Don't let echo_area_window to remain on a deleted frame.  */
   if (EQ (f->minibuffer_window, echo_area_window))
diff --git a/src/lisp.h b/src/lisp.h
index 56f24d82810..5f6721595c0 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4792,7 +4792,7 @@ fast_string_match_ignore_case (Lisp_Object regexp, Lisp_Object string)
 
 extern Lisp_Object Vminibuffer_list;
 extern Lisp_Object last_minibuf_string;
-extern void move_minibuffers_onto_frame (struct frame *, bool);
+extern void move_minibuffers_onto_frame (struct frame *, Lisp_Object, bool);
 extern bool is_minibuffer (EMACS_INT, Lisp_Object);
 extern EMACS_INT this_minibuffer_depth (Lisp_Object);
 extern EMACS_INT minibuf_level;
diff --git a/src/minibuf.c b/src/minibuf.c
index bedc5644807..aebd17c0b76 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -187,13 +187,15 @@ zip_minibuffer_stacks (Lisp_Object dest_window, Lisp_Object source_window)
 
 /* If `minibuffer_follows_selected_frame' is t, or we're about to
    delete a frame which potentially "contains" minibuffers, move them
-   from the old frame to the selected frame.  This function is
+   from the old frame to the to-be-selected frame.  This function is
    intended to be called from `do_switch_frame' in frame.c.  OF is the
-   old frame, FOR_DELETION is true if OF is about to be deleted.  */
+   old frame, SF is the to-be-selected frame, and FOR_DELETION is true
+   if OF is about to be deleted.  */
 void
-move_minibuffers_onto_frame (struct frame *of, bool for_deletion)
+move_minibuffers_onto_frame (struct frame *of, Lisp_Object sf,
+                             bool for_deletion)
 {
-  struct frame *f = XFRAME (selected_frame);
+  struct frame *f = XFRAME (sf);
 
   minibuf_window = f->minibuffer_window;
   if (!(minibuf_level
@@ -206,7 +208,7 @@ move_minibuffers_onto_frame (struct frame *of, bool for_deletion)
     {
       zip_minibuffer_stacks (f->minibuffer_window, of->minibuffer_window);
       if (for_deletion && XFRAME (MB_frame) != of)
-	MB_frame = selected_frame;
+	MB_frame = sf;
     }
 }