Avoid putting a dead buffer in the minibuffer window (Bug#72487)

* src/minibuf.c (minibuffer_unwind): Make sure that the buffer
referenced by the first element of the list of previous buffers
of the minibuffer window is live before assigning it to the
minibuffer window (Bug#72487).
* src/window.c (set_window_buffer): Assert that BUFFER is live.

2 files changed, 27 insertions, 15 deletions

diff --git a/src/minibuf.c b/src/minibuf.c
index 1dfee0a59c9..f16880011f7 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -63,7 +63,7 @@ Lisp_Object last_minibuf_string;
 
 static Lisp_Object minibuf_prompt;
 
-/* The frame containinug the most recently opened Minibuffer.  This is
+/* The frame containing the most recently opened minibuffer.  This is
    used only when `minibuffer-follows-selected-frame' is neither nil
    nor t.  */
 
@@ -1248,27 +1248,36 @@ static void
 minibuffer_unwind (void)
 {
   struct frame *f;
-  struct window *w;
-  Lisp_Object window;
-  Lisp_Object entry;
 
   if (NILP (exp_MB_frame)) return; /* "Can't happen." */
   f = XFRAME (exp_MB_frame);
-  window = f->minibuffer_window;
-  w = XWINDOW (window);
   if (FRAME_LIVE_P (f))
     {
-      /* minibuf_window = sf->minibuffer_window; */
-      if (!NILP (w->prev_buffers))
+      Lisp_Object window = f->minibuffer_window;
+
+      if (WINDOW_LIVE_P (window))
         {
-          entry = Fcar (w->prev_buffers);
-          w->prev_buffers = Fcdr (w->prev_buffers);
-          set_window_buffer (window, Fcar (entry), 0, 0);
-          Fset_window_start (window, Fcar (Fcdr (entry)), Qnil);
-          Fset_window_point (window, Fcar (Fcdr (Fcdr (entry))));
+          struct window *w = XWINDOW (window);
+
+          /* minibuf_window = sf->minibuffer_window; */
+          if (!NILP (w->prev_buffers))
+            {
+              Lisp_Object entry = Fcar (w->prev_buffers);
+
+              if (BUFFERP (Fcar (entry))
+                  && BUFFER_LIVE_P (XBUFFER (Fcar (entry))))
+                {
+                  wset_prev_buffers (w, Fcdr (w->prev_buffers));
+                  set_window_buffer (window, Fcar (entry), 0, 0);
+                  Fset_window_start (window, Fcar (Fcdr (entry)), Qnil);
+                  Fset_window_point (window, Fcar (Fcdr (Fcdr (entry))));
+                }
+              else
+                set_window_buffer (window, nth_minibuffer (0), 0, 0);
+            }
+          else
+            set_window_buffer (window, nth_minibuffer (0), 0, 0);
         }
-      else
-        set_window_buffer (window, nth_minibuffer (0), 0, 0);
     }
 }
 
diff --git a/src/window.c b/src/window.c
index ff28bac5306..dba2d6a3523 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4123,6 +4123,9 @@ set_window_buffer (Lisp_Object window, Lisp_Object buffer,
   specpdl_ref count = SPECPDL_INDEX ();
   bool samebuf = EQ (buffer, w->contents);
 
+  /* It's never OK to assign WINDOW a dead buffer.  */
+  eassert (BUFFER_LIVE_P (b));
+
   wset_buffer (w, buffer);
 
   if (EQ (window, selected_window))