vim-patch:8.2.2476: using freed memory when splitting window while closing buffer

Problem:    Using freed memory when using an autocommand to split a window
            while a buffer is being closed.
Solution:   Disallow splitting when the buffer has b_locked_split set.
983d83ff1c

Put the error message in window.c.
Cherry-pick a memory leak fix from Vim patch 8.2.0399.
Test still fails.

src/nvim/buffer.c

@@ -466,6 +466,7 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
   // When the buffer is no longer in a window, trigger BufWinLeave
   if (buf->b_nwindows == 1) {
     buf->b_locked++;
+    buf->b_locked_split++;
     if (apply_autocmds(EVENT_BUFWINLEAVE, buf->b_fname, buf->b_fname, false,
                        buf) && !bufref_valid(&bufref)) {
       // Autocommands deleted the buffer.
@@ -473,6 +474,7 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
       return false;
     }
     buf->b_locked--;
+    buf->b_locked_split--;
     if (abort_if_last && last_nonfloat(win)) {
       // Autocommands made this the only window.
       emsg(_(e_auabort));
@@ -483,6 +485,7 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
     // BufHidden
     if (!unload_buf) {
       buf->b_locked++;
+      buf->b_locked_split++;
       if (apply_autocmds(EVENT_BUFHIDDEN, buf->b_fname, buf->b_fname, false,
                          buf) && !bufref_valid(&bufref)) {
         // Autocommands deleted the buffer.
@@ -490,6 +493,7 @@ bool close_buffer(win_T *win, buf_T *buf, int action, bool abort_if_last, bool i
         return false;
       }
       buf->b_locked--;
+      buf->b_locked_split--;
       if (abort_if_last && last_nonfloat(win)) {
         // Autocommands made this the only window.
         emsg(_(e_auabort));
@@ -678,6 +682,7 @@ void buf_freeall(buf_T *buf, int flags)
 
   // Make sure the buffer isn't closed by autocommands.
   buf->b_locked++;
+  buf->b_locked_split++;
 
   bufref_T bufref;
   set_bufref(&bufref, buf);
@@ -703,6 +708,7 @@ void buf_freeall(buf_T *buf, int flags)
     return;
   }
   buf->b_locked--;
+  buf->b_locked_split--;
 
   // If the buffer was in curwin and the window has changed, go back to that
   // window, if it still exists.  This avoids that ":edit x" triggering a
@@ -1466,8 +1472,8 @@ void set_curbuf(buf_T *buf, int action)
   set_bufref(&prevbufref, prevbuf);
   set_bufref(&newbufref, buf);
 
-  // Autocommands may delete the current buffer and/or the buffer we want to go
+  // Autocommands may delete the current buffer and/or the buffer we want to
-  // to.  In those cases don't close the buffer.
+  // go to.  In those cases don't close the buffer.
   if (!apply_autocmds(EVENT_BUFLEAVE, NULL, NULL, false, curbuf)
       || (bufref_valid(&prevbufref) && bufref_valid(&newbufref)
           && !aborting())) {

src/nvim/buffer_defs.h

@@ -532,6 +532,8 @@ struct file_buffer {
   int b_flags;                  // various BF_ flags
   int b_locked;                 // Buffer is being closed or referenced, don't
                                 // let autocommands wipe it out.
+  int b_locked_split;           // Buffer is being closed, don't allow opening
+                                // a new window with it.
   int b_ro_locked;              // Non-zero when the buffer can't be changed.
                                 // Used for FileChangedRO
 

src/nvim/ex_getln.c

@@ -6376,6 +6376,7 @@ static int open_cmdwin(void)
   // Create a window for the command-line buffer.
   if (win_split((int)p_cwh, WSP_BOT) == FAIL) {
     beep_flush();
+    ga_clear(&winsizes);
     return K_IGNORE;
   }
   cmdwin_type = get_cmdline_type();

src/nvim/testdir/test_autocmd.vim

@@ -2717,17 +2717,14 @@ endfunc
 
 " Fuzzer found some strange combination that caused a crash.
 func Test_autocmd_normal_mess()
-  " TODO: why does this hang on Windows?
-  CheckNotMSWindows
-
   augroup aucmd_normal_test
     au BufLeave,BufWinLeave,BufHidden,BufUnload,BufDelete,BufWipeout * norm 7q/qc
   augroup END
   " Nvim has removed :open
-  " o4
+  " call assert_fails('o4', 'E1159')
-  e4
+  call assert_fails('e4', 'E1159')
   silent! H
-  e xx
+  call assert_fails('e xx', 'E1159')
   normal G
 
   augroup aucmd_normal_test
@@ -2749,7 +2746,7 @@ func Test_autocmd_vimgrep()
     au QuickfixCmdPre,BufNew,BufDelete,BufReadCmd * sb
     au QuickfixCmdPre,BufNew,BufDelete,BufReadCmd * q9
   augroup END
-  " TODO: if this is executed directly valgrind reports errors
+  %bwipe!
   call assert_fails('lv?a?', 'E926:')
 
   augroup aucmd_vimgrep

src/nvim/window.c

@@ -72,6 +72,9 @@ typedef enum {
   WEE_TRIGGER_LEAVE_AUTOCMDS = 0x10,
 } wee_flags_T;
 
+static char e_cannot_split_window_when_closing_buffer[]
+  = N_("E1159: Cannot split a window when closing the buffer");
+
 static char *m_onlyone = N_("Already only one window");
 
 /// When non-zero splitting a window is forbidden.  Used to avoid that nasty
@@ -946,6 +949,10 @@ static int check_split_disallowed(void)
     emsg(_("E242: Can't split a window while closing another"));
     return FAIL;
   }
+  if (curwin->w_buffer->b_locked_split) {
+    emsg(_(e_cannot_split_window_when_closing_buffer));
+    return FAIL;
+  }
   return OK;
 }
 
@@ -966,6 +973,10 @@ static int check_split_disallowed(void)
  */
 int win_split(int size, int flags)
 {
+  if (check_split_disallowed() == FAIL) {
+    return FAIL;
+  }
+
   // When the ":tab" modifier was used open a new tab page instead.
   if (may_open_tabpage() == OK) {
     return OK;
@@ -977,9 +988,6 @@ int win_split(int size, int flags)
     emsg(_("E442: Can't split topleft and botright at the same time"));
     return FAIL;
   }
-  if (check_split_disallowed() == FAIL) {
-    return FAIL;
-  }
 
   // When creating the help window make a snapshot of the window layout.
   // Otherwise clear the snapshot, it's now invalid.