Re: Stop frames stealing eachothers' minibuffers!

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Thu, Oct 22, 2020 at 19:14:09 +0300, Eli Zaretskii wrote:
> > Date: Wed, 21 Oct 2020 20:04:38 +0000
> > Cc: emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

> > Here's a corrected version of the patch, incorporating fixes and
> > suggestions from Stefan and Drew:

And below is a further amended patch.

> Thanks, I have a few minor comments:

> > +the user option @code{minibuffer-follows-frame} to @code{nil}, then

> I'd prefer to name the option minibuffer-follows-selected-frame.

OK.  I've changed it.

> > ++++
> > +** Switching frames when a minibuffer is active has been rationalized.

> "Rationalized"?  How about

>   Minibuffer behavior when selected frame changes can now be controlled.

> ?

What I've put in is

    ** Improved handling of minibuffers on switching frames.

.  How about that?

> > +By default, the active minibuffer is moved to the newly selected
> > +frame.  When the current command is continued (by completing the
> > +minibuffer action), it takes effect in the frame where the minibuffer
> > +was first opened.  An alternative behavior is available by customizing
> > +'minibuffer-follows-frame' to nil.  Here, the minibuffer stays in the
> > +frame where it was first opened, and you must switch back to this
> > +frame to continue or abort the current command.  The old (pre Emacs
> > +28.1) somewhat unsystematic behavior is no longer available.

> Can you reword to use less of passive tense here?

DONE.

> I may be missing something: where does this code handles the case of
> minibuffer-only frames?

The previous version didn't, really, very much.  The current version of
the patch contains quite a few changes, for example to suppress the
display of a ghost cursor in what had been a miniwindow.  I've tested a
little bit with an unusual configuration, 4 frames, of which 2 are
without minibuffers, one is a MB, and the last is a "normal" frame.  I
don't see anything untoward except, perhaps, the action of C-x o when
there are minibuffers open.  But that wasn't entirely predictable on the
unchanged master branch either.

Here's the latest version of the patch.  Comments would be appreciated:



diff --git a/doc/emacs/mini.texi b/doc/emacs/mini.texi
index 54f046a7e0..ede95a28d4 100644
--- a/doc/emacs/mini.texi
+++ b/doc/emacs/mini.texi
@@ -69,6 +69,17 @@ Basic Minibuffer
 the minibuffer comes back.  While the minibuffer is in use, Emacs does
 not echo keystrokes.
 
+@vindex minibuffer-follows-selected-frame
+  While using the minibuffer, you can switch to a different frame,
+perhaps to note text you need to enter (@pxref{Frame Commands}).  By
+default, the active minibuffer moves to this new frame.  If you set
+the user option @code{minibuffer-follows-selected-frame} to
+@code{nil}, then the minibuffer stays in the frame where you opened
+it, and you must switch back to that frame in order to complete (or
+abort) the current command.  Note that the effect of the command, when
+you finally finish using the minibuffer, always takes place in the
+frame where you first opened it.
+
 @node Minibuffer File
 @section Minibuffers for File Names
 
diff --git a/etc/NEWS b/etc/NEWS
index 4cc66aef6b..2489706d89 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -85,6 +85,17 @@ useful on systems such as FreeBSD which ships only with "etc/termcap".
 \f
 * Changes in Emacs 28.1
 
++++
+** Improved handling of minibuffers on switching frames.
+By default, an active minibuffer now moves to a newly selected frame.
+When continuing the current command (by completing the minibuffer
+action), the effect happens in the frame where the minibuffer was
+first opened.  An alternative behavior is available by customizing
+'minibuffer-follows-selected-frame' to nil.  Here, the minibuffer
+stays in the frame where you first opened it, and you must switch back
+to this frame to continue or abort its command.  The old, somewhat
+unsystematic behavior is no longer available.
+
 +++
 ** New system for displaying documentation for groups of function.
 This can either be used by saying 'M-x shortdoc-display-group' and
diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 6927b6df6b..04fb1dc6d0 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -394,6 +394,7 @@ minibuffer-prompt-properties--setter
 	     ;;    			(directory :format "%v"))))
 	     (load-prefer-newer lisp boolean "24.4")
 	     ;; minibuf.c
+             (minibuffer-follows-selected-frame minibuffer boolean "28.1")
 	     (enable-recursive-minibuffers minibuffer boolean)
 	     (history-length minibuffer
 			     (choice (const :tag "Infinite" t) integer)
diff --git a/lisp/minibuffer.el b/lisp/minibuffer.el
index 5a41e2f30b..9d57a817b2 100644
--- a/lisp/minibuffer.el
+++ b/lisp/minibuffer.el
@@ -701,7 +701,7 @@ minibuffer-message
 or until the next input event arrives, whichever comes first.
 Enclose MESSAGE in [...] if this is not yet the case.
 If ARGS are provided, then pass MESSAGE through `format-message'."
-  (if (not (minibufferp (current-buffer)))
+  (if (not (minibufferp (current-buffer) t))
       (progn
         (if args
             (apply #'message message args)
diff --git a/src/frame.c b/src/frame.c
index 7c377da445..512aaf5f45 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -1482,6 +1482,7 @@ do_switch_frame (Lisp_Object frame, int track, int for_deletion, Lisp_Object nor
 #endif
     internal_last_event_frame = Qnil;
 
+  move_minibuffer_onto_frame ();
   return frame;
 }
 
diff --git a/src/lisp.h b/src/lisp.h
index 45353fbef3..548eebc9c7 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4336,6 +4336,8 @@ extern void clear_regexp_cache (void);
 
 extern Lisp_Object Vminibuffer_list;
 extern Lisp_Object last_minibuf_string;
+extern void move_minibuffer_onto_frame (void);
+extern bool is_minibuffer (EMACS_INT, Lisp_Object);
 extern Lisp_Object get_minibuffer (EMACS_INT);
 extern void init_minibuf_once (void);
 extern void syms_of_minibuf (void);
diff --git a/src/minibuf.c b/src/minibuf.c
index f957b2ae17..11b5eec236 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -64,6 +64,12 @@ static Lisp_Object minibuf_prompt;
 static ptrdiff_t minibuf_prompt_width;
 
 \f
+static bool
+minibuf_follows_frame (void)
+{
+  return !NILP (Fdefault_toplevel_value (Qminibuffer_follows_selected_frame));
+}
+
 /* Put minibuf on currently selected frame's minibuffer.
    We do this whenever the user starts a new minibuffer
    or when a minibuffer exits.  */
@@ -76,37 +82,73 @@ choose_minibuf_frame (void)
       && !EQ (minibuf_window, XFRAME (selected_frame)->minibuffer_window))
     {
       struct frame *sf = XFRAME (selected_frame);
-      Lisp_Object buffer;
-
       /* I don't think that any frames may validly have a null minibuffer
 	 window anymore.  */
       if (NILP (sf->minibuffer_window))
 	emacs_abort ();
 
-      /* Under X, we come here with minibuf_window being the
-	 minibuffer window of the unused termcap window created in
-	 init_window_once.  That window doesn't have a buffer.  */
-      buffer = XWINDOW (minibuf_window)->contents;
-      if (BUFFERP (buffer))
-	/* Use set_window_buffer instead of Fset_window_buffer (see
-	   discussion of bug#11984, bug#12025, bug#12026).  */
-	set_window_buffer (sf->minibuffer_window, buffer, 0, 0);
-      minibuf_window = sf->minibuffer_window;
+      if (minibuf_follows_frame ())
+        minibuf_window = sf->minibuffer_window;
+      else if (minibuf_level)
+        {
+          Lisp_Object buffer = get_minibuffer (minibuf_level);
+          Lisp_Object tail, frame;
+
+          minibuf_window = sf->minibuffer_window;
+          FOR_EACH_FRAME (tail, frame)
+            if (EQ (XWINDOW (XFRAME (frame)->minibuffer_window)->contents,
+                    buffer))
+              {
+                minibuf_window = XFRAME (frame)->minibuffer_window;
+                break;
+              }
+        }
+      else
+        minibuf_window = Qnil;
     }
 
-  /* Make sure no other frame has a minibuffer as its selected window,
-     because the text would not be displayed in it, and that would be
-     confusing.  Only allow the selected frame to do this,
-     and that only if the minibuffer is active.  */
-  {
-    Lisp_Object tail, frame;
+  if (minibuf_follows_frame ())
+    /* Make sure no other frame has a minibuffer as its selected window,
+       because the text would not be displayed in it, and that would be
+       confusing.  Only allow the selected frame to do this,
+       and that only if the minibuffer is active.  */
+    {
+      Lisp_Object tail, frame;
 
-    FOR_EACH_FRAME (tail, frame)
-      if (MINI_WINDOW_P (XWINDOW (FRAME_SELECTED_WINDOW (XFRAME (frame))))
-	  && !(EQ (frame, selected_frame)
-	       && minibuf_level > 0))
-	Fset_frame_selected_window (frame, Fframe_first_window (frame), Qnil);
-  }
+      FOR_EACH_FRAME (tail, frame)
+        if (MINI_WINDOW_P (XWINDOW (FRAME_SELECTED_WINDOW (XFRAME (frame))))
+            && !(EQ (frame, selected_frame)
+                 && minibuf_level > 0))
+          Fset_frame_selected_window (frame, Fframe_first_window (frame), Qnil);
+    }
+}
+
+/* If `minibuffer_follows_selected_frame' and we have a minibuffer, move it
+   from its current frame to the selected frame.  This function is
+   intended to be called from `do_switch_frame' in frame.c.  */
+void move_minibuffer_onto_frame (void)
+{
+  if (!minibuf_level)
+    return;
+  if (!minibuf_follows_frame ())
+    return;
+  if (FRAMEP (selected_frame)
+      && FRAME_LIVE_P (XFRAME (selected_frame))
+      && !EQ (minibuf_window, XFRAME (selected_frame)->minibuffer_window))
+    {
+      struct frame *sf = XFRAME (selected_frame);
+      Lisp_Object old_frame = XWINDOW (minibuf_window)->frame;
+      struct frame *of = XFRAME (old_frame);
+      Lisp_Object buffer = XWINDOW (minibuf_window)->contents;
+
+      set_window_buffer (sf->minibuffer_window, buffer, 0, 0);
+      minibuf_window = sf->minibuffer_window;
+      if (XWINDOW (minibuf_window)->frame == selected_frame)
+        /* The minibuffer might be on another frame. */
+        Fset_frame_selected_window (selected_frame, sf->minibuffer_window,
+                                    Qnil);
+      set_window_buffer (of->minibuffer_window, get_minibuffer (0), 0, 0);
+    }
 }
 
 DEFUN ("active-minibuffer-window", Factive_minibuffer_window,
@@ -262,13 +304,15 @@ read_minibuf_noninteractive (Lisp_Object prompt, bool expflag,
 }
 \f
 DEFUN ("minibufferp", Fminibufferp,
-       Sminibufferp, 0, 1, 0,
+       Sminibufferp, 0, 2, 0,
        doc: /* Return t if BUFFER is a minibuffer.
 No argument or nil as argument means use current buffer as BUFFER.
-BUFFER can be a buffer or a buffer name.  */)
-  (Lisp_Object buffer)
+BUFFER can be a buffer or a buffer name.  If LIVE is non-nil, then
+t will be returned only if BUFFER is an active minibuffer.  */)
+  (Lisp_Object buffer, Lisp_Object live)
 {
   Lisp_Object tem;
+  EMACS_INT i;
 
   if (NILP (buffer))
     buffer = Fcurrent_buffer ();
@@ -277,8 +321,22 @@ BUFFER can be a buffer or a buffer name.  */)
   else
     CHECK_BUFFER (buffer);
 
-  tem = Fmemq (buffer, Vminibuffer_list);
-  return ! NILP (tem) ? Qt : Qnil;
+  /* tem = Fmemq (buffer, Vminibuffer_list); */
+  /* return (!NILP (tem) && !EQ (tem, Vminibuffer_list)) ? Qt : Qnil; */
+  if (!NILP (live))
+    return !NILP (Fmemq (buffer, Vminibuffer_list)) ? Qt : Qnil;
+  if (EQ (buffer, Fcar (Vminibuffer_list)))
+    /*  *Minibuf-0* is never active.  */
+    return Qnil;
+  tem = Fcdr (Vminibuffer_list);
+  for (i = 1; i <= minibuf_level; i++)
+    {
+      if (NILP (tem))
+        return Qnil;
+      if (EQ (Fcar (tem), buffer))
+        return Qt;
+    }
+  return Qnil;
 }
 
 DEFUN ("minibuffer-prompt-end", Fminibuffer_prompt_end,
@@ -362,9 +420,6 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
   Lisp_Object histstring;
   Lisp_Object histval;
 
-  Lisp_Object empty_minibuf;
-  Lisp_Object dummy, frame;
-
   specbind (Qminibuffer_default, defalt);
   specbind (Qinhibit_read_only, Qnil);
 
@@ -416,11 +471,12 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
     {
       Lisp_Object str
 	= build_string ("Command attempted to use minibuffer while in minibuffer");
-      if (EQ (selected_window, minibuf_window))
-	Fsignal (Quser_error, (list1 (str)));
+      if (!minibuf_follows_frame ()
+          || EQ (selected_window, minibuf_window))
+        Fsignal (Quser_error, (list1 (str)));
       else
-	/* If we're in another window, cancel the minibuffer that's active.  */
-	Fthrow (Qexit, str);
+        /* If we're in another window, cancel the minibuffer that's active.  */
+        Fthrow (Qexit, str);
     }
 
   if ((noninteractive
@@ -433,6 +489,8 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
       return unbind_to (count, val);
     }
 
+  minibuf_level++;         /* Before calling choose_minibuf_frame.  */
+
   /* Choose the minibuffer window and frame, and take action on them.  */
 
   /* Prepare for restoring the current buffer since choose_minibuf_frame
@@ -484,7 +542,6 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
     = Fcons (Fthis_command_keys_vector (), minibuf_save_list);
 
   record_unwind_protect_void (read_minibuf_unwind);
-  minibuf_level++;
   /* We are exiting the minibuffer one way or the other, so run the hook.
      It should be run before unwinding the minibuf settings.  Do it
      separately from read_minibuf_unwind because we need to make sure that
@@ -566,23 +623,6 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
   if (minibuf_level == 1 || !EQ (minibuf_window, selected_window))
     minibuf_selected_window = selected_window;
 
-  /* Empty out the minibuffers of all frames other than the one
-     where we are going to display one now.
-     Set them to point to ` *Minibuf-0*', which is always empty.  */
-  empty_minibuf = get_minibuffer (0);
-
-  FOR_EACH_FRAME (dummy, frame)
-    {
-      Lisp_Object root_window = Fframe_root_window (frame);
-      Lisp_Object mini_window = XWINDOW (root_window)->next;
-
-      if (! NILP (mini_window) && ! EQ (mini_window, minibuf_window)
-	  && !NILP (Fwindow_minibuffer_p (mini_window)))
-	/* Use set_window_buffer instead of Fset_window_buffer (see
-	   discussion of bug#11984, bug#12025, bug#12026).  */
-	set_window_buffer (mini_window, empty_minibuf, 0, 0);
-    }
-
   /* Display this minibuffer in the proper window.  */
   /* Use set_window_buffer instead of Fset_window_buffer (see
      discussion of bug#11984, bug#12025, bug#12026).  */
@@ -714,6 +754,16 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
   return val;
 }
 
+/* Returns whether a Lisp_Object is a particular existing minibuffer.  */
+bool
+is_minibuffer (EMACS_INT depth, Lisp_Object buf)
+{
+  Lisp_Object tail = Fnthcdr (make_fixnum (depth), Vminibuffer_list);
+  return
+    !NILP (tail)
+    && EQ (Fcar (tail), buf);
+}
+
 /* Return a buffer to be used as the minibuffer at depth `depth'.
    depth = 0 is the lowest allowed argument, and that is the value
    used for nonrecursive minibuffer invocations.  */
@@ -775,6 +825,7 @@ read_minibuf_unwind (void)
 {
   Lisp_Object old_deactivate_mark;
   Lisp_Object window;
+  Lisp_Object future_mini_window;
 
   /* If this was a recursive minibuffer,
      tie the minibuffer window back to the outer level minibuffer buffer.  */
@@ -809,6 +860,7 @@ read_minibuf_unwind (void)
   if (FRAME_LIVE_P (XFRAME (WINDOW_FRAME (XWINDOW (temp)))))
     minibuf_window = temp;
 #endif
+  future_mini_window = Fcar (minibuf_save_list);
   minibuf_save_list = Fcdr (minibuf_save_list);
 
   /* Erase the minibuffer we were using at this level.  */
@@ -825,7 +877,8 @@ read_minibuf_unwind (void)
 
   /* When we get to the outmost level, make sure we resize the
      mini-window back to its normal size.  */
-  if (minibuf_level == 0)
+  if (minibuf_level == 0
+      || !EQ (selected_frame, WINDOW_FRAME (XWINDOW (future_mini_window))))
     resize_mini_window (XWINDOW (window), 0);
 
   /* Deal with frames that should be removed when exiting the
@@ -1911,6 +1964,8 @@ syms_of_minibuf (void)
   staticpro (&minibuf_prompt);
   staticpro (&minibuf_save_list);
 
+  DEFSYM (Qminibuffer_follows_selected_frame,
+          "minibuffer-follows-selected-frame");
   DEFSYM (Qcompletion_ignore_case, "completion-ignore-case");
   DEFSYM (Qminibuffer_default, "minibuffer-default");
   Fset (Qminibuffer_default, Qnil);
@@ -1954,6 +2009,14 @@ For example, `eval-expression' uses this.  */);
 The function is called with the arguments passed to `read-buffer'.  */);
   Vread_buffer_function = Qnil;
 
+  DEFVAR_BOOL ("minibuffer-follows-selected-frame", minibuffer_follows_selected_frame,
+               doc: /* Non-nil means an open minibuffer will move to a newly selected frame.
+Nil means that a minibuffer will appear only in the frame which created it.
+
+Any buffer local or dynamic binding of this variable is ignored.  Only the
+default top level value is used.  */);
+  minibuffer_follows_selected_frame = 1;
+
   DEFVAR_BOOL ("read-buffer-completion-ignore-case",
 	       read_buffer_completion_ignore_case,
 	       doc: /* Non-nil means completion ignores case when reading a buffer name.  */);
diff --git a/src/window.c b/src/window.c
index e7433969d2..2eba509727 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2643,8 +2643,10 @@ candidate_window_p (Lisp_Object window, Lisp_Object owindow,
     /* 	To qualify as candidate, it's not sufficient for WINDOW's frame
 	to just share the minibuffer window - it must be active as well
 	(see Bug#24500).  */
-    candidate_p = (EQ (XWINDOW (all_frames)->frame, w->frame)
-		   || EQ (XWINDOW (all_frames)->frame, FRAME_FOCUS_FRAME (f)));
+    candidate_p = ((EQ (XWINDOW (all_frames)->frame, w->frame)
+                    || (EQ (f->minibuffer_window, all_frames)
+                        && EQ (XWINDOW (all_frames)->frame, FRAME_FOCUS_FRAME (f))))
+                   && !is_minibuffer (0, XWINDOW (all_frames)->contents));
   else if (FRAMEP (all_frames))
     candidate_p = EQ (all_frames, w->frame);
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 0e5dffbe00..0dfe34a011 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -31220,7 +31220,9 @@ get_window_cursor_type (struct window *w, struct glyph *glyph, int *width,
     {
       *active_cursor = false;
 
-      if (MINI_WINDOW_P (w) && minibuf_level == 0)
+      if (MINI_WINDOW_P (w) &&
+          (minibuf_level == 0
+           || is_minibuffer (0, w->contents)))
 	return NO_CURSOR;
 
       non_selected = true;


-- 
Alan Mackenzie (Nuremberg, Germany).