Various detailed fixes to minibuf.c, etc., to fix bug #48337

Also fix some unsafe coding.

* lisp/window.el (push-window-buffer-onto-prev): New function, extracted from
(record-window-buffer): Refactor by extracting the above, and removing the now
redundant parameter DO-MINIBUF.

* src/minibuf.c (zip_minibuffer_stacks, read_minibuf): Replace calls to
get_minibuffer (0) by nth_minibuffer (0).  Replace calls to
Qrecord_window_buffer by calls to Qpush_window_buffer_onto_prev.
(Factive_minibuffer_window, read_minibuf_unwind): Call abort_emacs should an
"impossible" null value be returned by nth_minibuffer.
(read_minibuf): Move the get_minibuffer_call to just after the incrementation
of minibuf_level as a precaution against a missing buffer in
Vminibuffer_list.
(nth_minibuffer): Replace XCAR by Fcar, to allow (car nil) to work.
(init_minibuf_once): Create the inactive buffer  *Minibuf-0*.
(syms_of_minibuf): New DEFSYM, Qpush_window_buffer_onto_prev.

* src/window.c (restore_window_configuration): Replace some XCARs and XCDRs
by Fcar_safe and Fcdr_safe.

1 files changed, 22 insertions, 13 deletions

diff --git a/src/minibuf.c b/src/minibuf.c
index 52d1275451b..428998a639b 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -157,16 +157,15 @@ zip_minibuffer_stacks (Lisp_Object dest_window, Lisp_Object source_window)
       Fset_window_start (dest_window, Fwindow_start (source_window), Qnil);
       Fset_window_point (dest_window, Fwindow_point (source_window));
       dw->prev_buffers = sw->prev_buffers;
-      set_window_buffer (source_window, get_minibuffer (0), 0, 0);
+      set_window_buffer (source_window, nth_minibuffer (0), 0, 0);
       sw->prev_buffers = Qnil;
       return;
     }
 
   if (live_minibuffer_p (dw->contents))
-    call2 (Qrecord_window_buffer, dest_window, Qt);
+    call1 (Qpush_window_buffer_onto_prev, dest_window);
   if (live_minibuffer_p (sw->contents))
-    call2 (Qrecord_window_buffer, source_window, Qt);
-
+    call1 (Qpush_window_buffer_onto_prev, source_window);
   acc = merge_c (dw->prev_buffers, sw->prev_buffers, minibuffer_ent_greater);
 
   if (!NILP (acc))
@@ -179,7 +178,7 @@ zip_minibuffer_stacks (Lisp_Object dest_window, Lisp_Object source_window)
     }
   dw->prev_buffers = acc;
   sw->prev_buffers = Qnil;
-  set_window_buffer (source_window, get_minibuffer (0), 0, 0);
+  set_window_buffer (source_window, nth_minibuffer (0), 0, 0);
 }
 
 /* If `minibuffer_follows_selected_frame' is t, or we're about to
@@ -228,6 +227,8 @@ DEFUN ("active-minibuffer-window", Factive_minibuffer_window,
     return Qnil;
 
   innermost_MB = nth_minibuffer (minibuf_level);
+  if (NILP (innermost_MB))
+    emacs_abort ();
   FOR_EACH_FRAME (frames, frame)
     {
       f = XFRAME (frame);
@@ -653,6 +654,10 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
     }
 
   minibuf_level++;         /* Before calling choose_minibuf_frame.  */
+  /* Ensure now that the latest minibuffer has been created, in case
+     anything happens which depends on MINNIBUF_LEVEL and
+     Vminibuffer_list being consistent with eachother.  */
+  minibuffer = get_minibuffer (minibuf_level);
 
   /* Choose the minibuffer window and frame, and take action on them.  */
 
@@ -680,7 +685,7 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
     }
   MB_frame = XWINDOW (XFRAME (selected_frame)->minibuffer_window)->frame;
   if (live_minibuffer_p (XWINDOW (minibuf_window)->contents))
-    call2 (Qrecord_window_buffer, minibuf_window, Qt);
+    call1 (Qpush_window_buffer_onto_prev, minibuf_window);
 
   record_unwind_protect_void (minibuffer_unwind);
   record_unwind_protect (restore_window_configuration,
@@ -766,7 +771,6 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
 
   /* Switch to the minibuffer.  */
 
-  minibuffer = get_minibuffer (minibuf_level);
   set_minibuffer_mode (minibuffer, minibuf_level);
   Fset_buffer (minibuffer);
 
@@ -807,7 +811,7 @@ read_minibuf (Lisp_Object map, Lisp_Object initial, Lisp_Object prompt,
   /* Empty out the minibuffers of all frames, except those frames
      where there is an active minibuffer.
      Set them to point to ` *Minibuf-0*', which is always empty.  */
-  empty_minibuf = get_minibuffer (0);
+  empty_minibuf = nth_minibuffer (0);
   set_minibuffer_mode (empty_minibuf, 0);
 
   /* Display this minibuffer in the proper window.  */
@@ -969,9 +973,7 @@ static Lisp_Object
 nth_minibuffer (EMACS_INT depth)
 {
   Lisp_Object tail = Fnthcdr (make_fixnum (depth), Vminibuffer_list);
-  if (NILP (tail))
-    return Qnil;
-  return XCAR (tail);
+  return Fcar (tail);
 }
 
 /* Set the major mode of the minibuffer BUF, depending on DEPTH, the
@@ -1076,9 +1078,13 @@ read_minibuf_unwind (void)
   Lisp_Object future_mini_window;
   Lisp_Object saved_selected_frame = selected_frame;
   Lisp_Object window, frames;
+  Lisp_Object expired_MB = nth_minibuffer (minibuf_level);
   struct window *w;
   struct frame *f;
 
+  if (NILP (expired_MB))
+    emacs_abort ();
+
   /* Locate the expired minibuffer.  */
   FOR_EACH_FRAME (frames, exp_MB_frame)
     {
@@ -1088,7 +1094,7 @@ read_minibuf_unwind (void)
 	{
 	  w = XWINDOW (window);
 	  if (EQ (w->frame, exp_MB_frame)
-	      && EQ (w->contents, nth_minibuffer (minibuf_level)))
+	      && EQ (w->contents, expired_MB))
 	    goto found;
 	}
     }
@@ -1104,7 +1110,7 @@ read_minibuf_unwind (void)
      minibuffer when we reset the relevant variables.  Don't depend on
      `minibuf_window' here.  This could by now be the mini-window of any
      frame.  */
-  Fset_buffer (nth_minibuffer (minibuf_level));
+  Fset_buffer (expired_MB);
   minibuf_level--;
 
   /* Restore prompt, etc, from outer minibuffer level.  */
@@ -2272,6 +2278,8 @@ init_minibuf_once (void)
   staticpro (&Vminibuffer_list);
   staticpro (&Vcommand_loop_level_list);
   pdumper_do_now_and_after_load (init_minibuf_once_for_pdumper);
+  /* Ensure our inactive minibuffer exists.  */
+  get_minibuffer (0);
 }
 
 static void
@@ -2337,6 +2345,7 @@ syms_of_minibuf (void)
   DEFSYM (Qminibuffer_completing_file_name, "minibuffer-completing-file-name");
   DEFSYM (Qselect_frame_set_input_focus, "select-frame-set-input-focus");
   DEFSYM (Qadd_to_history, "add-to-history");
+  DEFSYM (Qpush_window_buffer_onto_prev, "push-window-buffer-onto-prev");
 
   DEFVAR_LISP ("read-expression-history", Vread_expression_history,
 	       doc: /* A history list for arguments that are Lisp expressions to evaluate.