vim-patch:8.2.4631: crash when switching window in BufWipeout autocommand

Problem:    Crash when switching window in BufWipeout autocommand.
Solution:   Put any buffer in the window to avoid it being NULL.
            (closes vim/vim#10024)
347538fad0

win_init_empty() cannot be made static because it is used in autocmd.c

src/nvim/buffer.c

@@ -590,6 +590,10 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last)
 
   // Remove the buffer from the list.
   if (wipe_buf) {
+    // Do not wipe out the buffer if it is used in a window.
+    if (buf->b_nwindows > 0) {
+      return false;
+    }
     if (buf->b_sfname != buf->b_ffname) {
       XFREE_CLEAR(buf->b_sfname);
     } else {

src/nvim/testdir/test_autocmd.vim

@@ -2611,4 +2611,21 @@ func Test_autocmd_closing_cmdwin()
   only
 endfunc
 
+func Test_bufwipeout_changes_window()
+  " This should not crash, but we don't have any expectations about what
+  " happens, changing window in BufWipeout has unpredictable results.
+  tabedit
+  let g:window_id = win_getid()
+  topleft new
+  setlocal bufhidden=wipe
+  autocmd BufWipeout <buffer> call win_gotoid(g:window_id)
+  tabprevious
+  +tabclose
+
+  unlet g:window_id
+  au! BufWipeout
+  %bwipe!
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab

src/nvim/window.c

@@ -2350,6 +2350,30 @@ void entering_window(win_T *const win)
   }
 }
 
+void win_init_empty(win_T *wp)
+{
+  redraw_later(wp, NOT_VALID);
+  wp->w_lines_valid = 0;
+  wp->w_cursor.lnum = 1;
+  wp->w_curswant = wp->w_cursor.col = 0;
+  wp->w_cursor.coladd = 0;
+  wp->w_pcmark.lnum = 1;        // pcmark not cleared but set to line 1
+  wp->w_pcmark.col = 0;
+  wp->w_prev_pcmark.lnum = 0;
+  wp->w_prev_pcmark.col = 0;
+  wp->w_topline = 1;
+  wp->w_topfill = 0;
+  wp->w_botline = 2;
+  wp->w_s = &wp->w_buffer->b_s;
+}
+
+/// Init the current window "curwin".
+/// Called when a new file is being edited.
+void curwin_init(void)
+{
+  win_init_empty(curwin);
+}
+
 /// Closes all windows for buffer `buf` unless there is only one non-floating window.
 ///
 /// @param keep_curwin  don't close `curwin`
@@ -2867,6 +2891,13 @@ void win_close_othertab(win_T *win, int free_buf, tabpage_T *tp)
   for (ptp = first_tabpage; ptp != NULL && ptp != tp; ptp = ptp->tp_next) {
   }
   if (ptp == NULL || tp == curtab) {
+    // If the buffer was removed from the window we have to give it any
+    // buffer.
+    if (win_valid_any_tab(win) && win->w_buffer == NULL) {
+      win->w_buffer = firstbuf;
+      firstbuf->b_nwindows++;
+      win_init_empty(win);
+    }
     return;
   }
 
@@ -3793,33 +3824,6 @@ void close_others(int message, int forceit)
   }
 }
 
-
-/*
- * Init the current window "curwin".
- * Called when a new file is being edited.
- */
-void curwin_init(void)
-{
-  win_init_empty(curwin);
-}
-
-void win_init_empty(win_T *wp)
-{
-  redraw_later(wp, NOT_VALID);
-  wp->w_lines_valid = 0;
-  wp->w_cursor.lnum = 1;
-  wp->w_curswant = wp->w_cursor.col = 0;
-  wp->w_cursor.coladd = 0;
-  wp->w_pcmark.lnum = 1;        // pcmark not cleared but set to line 1
-  wp->w_pcmark.col = 0;
-  wp->w_prev_pcmark.lnum = 0;
-  wp->w_prev_pcmark.col = 0;
-  wp->w_topline = 1;
-  wp->w_topfill = 0;
-  wp->w_botline = 2;
-  wp->w_s = &wp->w_buffer->b_s;
-}
-
 /*
  * Allocate the first window and put an empty buffer in it.
  * Called from main().