patch 8.2.3591: no event is triggered when closing a window

Problem:    No event is triggered when closing a window.
Solution:   Add the WinClosed event. (Naohiro Ono, closes #9110)

runtime/doc/autocmd.txt

@@ -348,6 +348,7 @@ Name			triggered by ~
 
 |WinNew|		after creating a new window
 |TabNew|		after creating a new tab page
+|WinClosed|		after closing a window
 |TabClosed|		after closing a tab page
 |WinEnter|		after entering another window
 |WinLeave|		before leaving a window
@@ -1280,6 +1281,12 @@ VimResume			When the Vim instance is resumed after being
 VimSuspend			When the Vim instance is suspended.  Only when
 				CTRL-Z was typed inside Vim, not when the
 				SIGSTOP or SIGTSTP signal was sent to Vim.
+							*WinClosed*
+WinClosed			After closing a window.  The pattern is
+				matched against the |window-ID|.  Both
+				<amatch> and <afile> are set to the
+				|window-ID|.  Non-recursive (event cannot
+				trigger itself).
 							*WinEnter*
 WinEnter			After entering another window.  Not done for
 				the first window, when Vim has just started.

src/autocmd.c

@@ -186,6 +186,7 @@ static struct event_name
     {"VimLeave",	EVENT_VIMLEAVE},
     {"VimLeavePre",	EVENT_VIMLEAVEPRE},
     {"WinNew",		EVENT_WINNEW},
+    {"WinClosed",	EVENT_WINCLOSED},
     {"WinEnter",	EVENT_WINENTER},
     {"WinLeave",	EVENT_WINLEAVE},
     {"VimResized",	EVENT_VIMRESIZED},
@@ -2042,7 +2043,8 @@ apply_autocmds_group(
 		|| event == EVENT_OPTIONSET
 		|| event == EVENT_QUICKFIXCMDPOST
 		|| event == EVENT_DIRCHANGED
-		|| event == EVENT_MODECHANGED)
+		|| event == EVENT_MODECHANGED
+		|| event == EVENT_WINCLOSED)
 	{
 	    fname = vim_strsave(fname);
 	    autocmd_fname_full = TRUE; // don't expand it later

src/testdir/test_autocmd.vim

@@ -270,6 +270,7 @@ func Test_win_tab_autocmd()
 
   augroup testing
     au WinNew * call add(g:record, 'WinNew')
+    au WinClosed * call add(g:record, 'WinClosed')
     au WinEnter * call add(g:record, 'WinEnter') 
     au WinLeave * call add(g:record, 'WinLeave') 
     au TabNew * call add(g:record, 'TabNew')
@@ -286,8 +287,8 @@ func Test_win_tab_autocmd()
   call assert_equal([
 	\ 'WinLeave', 'WinNew', 'WinEnter',
 	\ 'WinLeave', 'TabLeave', 'WinNew', 'WinEnter', 'TabNew', 'TabEnter',
-	\ 'WinLeave', 'TabLeave', 'TabClosed', 'WinEnter', 'TabEnter',
-	\ 'WinLeave', 'WinEnter'
+	\ 'WinLeave', 'TabLeave', 'WinClosed', 'TabClosed', 'WinEnter', 'TabEnter',
+	\ 'WinLeave', 'WinClosed', 'WinEnter'
 	\ ], g:record)
 
   let g:record = []
@@ -298,7 +299,7 @@ func Test_win_tab_autocmd()
   call assert_equal([
 	\ 'WinLeave', 'TabLeave', 'WinNew', 'WinEnter', 'TabNew', 'TabEnter',
 	\ 'WinLeave', 'TabLeave', 'WinEnter', 'TabEnter',
-	\ 'TabClosed'
+	\ 'WinClosed', 'TabClosed'
 	\ ], g:record)
 
   augroup testing
@@ -307,6 +308,45 @@ func Test_win_tab_autocmd()
   unlet g:record
 endfunc
 
+func Test_WinClosed()
+  " Test that the pattern is matched against the closed window's ID, and both
+  " <amatch> and <afile> are set to it.
+  new
+  let winid = win_getid()
+  let g:matched = v:false
+  augroup test-WinClosed
+    autocmd!
+    execute 'autocmd WinClosed' winid 'let g:matched = v:true'
+    autocmd WinClosed * let g:amatch = str2nr(expand('<amatch>'))
+    autocmd WinClosed * let g:afile = str2nr(expand('<afile>'))
+  augroup END
+  close
+  call assert_true(g:matched)
+  call assert_equal(winid, g:amatch)
+  call assert_equal(winid, g:afile)
+
+  " Test that WinClosed is non-recursive.
+  new
+  new
+  call assert_equal(3, winnr('$'))
+  let g:triggered = 0
+  augroup test-WinClosed
+    autocmd!
+    autocmd WinClosed * let g:triggered += 1
+    autocmd WinClosed * 2 wincmd c
+  augroup END
+  close
+  call assert_equal(1, winnr('$'))
+  call assert_equal(1, g:triggered)
+
+  autocmd! test-WinClosed
+  augroup! test-WinClosed
+  unlet g:matched
+  unlet g:amatch
+  unlet g:afile
+  unlet g:triggered
+endfunc
+
 func s:AddAnAutocmd()
   augroup vimBarTest
     au BufReadCmd * echo 'hello'

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3591,
 /**/
     3590,
 /**/

src/vim.h

@@ -1379,6 +1379,7 @@ enum auto_event
     EVENT_WINENTER,		// after entering a window
     EVENT_WINLEAVE,		// before leaving a window
     EVENT_WINNEW,		// when entering a new window
+    EVENT_WINCLOSED,		// after closing a window
     EVENT_VIMSUSPEND,		// before Vim is suspended
     EVENT_VIMRESUME,		// after Vim is resumed
 

src/window.c

@@ -19,6 +19,7 @@ static void win_exchange(long);
 static void win_rotate(int, int);
 static void win_totop(int size, int flags);
 static void win_equal_rec(win_T *next_curwin, int current, frame_T *topfr, int dir, int col, int row, int width, int height);
+static void trigger_winclosed(win_T *win);
 static win_T *win_free_mem(win_T *win, int *dirp, tabpage_T *tp);
 static frame_T *win_altframe(win_T *win, tabpage_T *tp);
 static tabpage_T *alt_tabpage(void);
@@ -2566,6 +2567,13 @@ win_close(win_T *win, int free_buf)
     if (popup_win_closed(win) && !win_valid(win))
 	return FAIL;
 #endif
+
+    // Trigger WinClosed just before starting to free window-related resources.
+    trigger_winclosed(win);
+    // autocmd may have freed the window already.
+    if (!win_valid_any_tab(win))
+	return OK;
+
     win_close_buffer(win, free_buf ? DOBUF_UNLOAD : 0, TRUE);
 
     if (only_one_window() && win_valid(win) && win->w_buffer == NULL
@@ -2710,6 +2718,20 @@ win_close(win_T *win, int free_buf)
     return OK;
 }
 
+    static void
+trigger_winclosed(win_T *win)
+{
+    static int	recursive = FALSE;
+    char_u	winid[NUMBUFLEN];
+
+    if (recursive)
+	return;
+    recursive = TRUE;
+    vim_snprintf((char *)winid, sizeof(winid), "%i", win->w_id);
+    apply_autocmds(EVENT_WINCLOSED, winid, winid, FALSE, win->w_buffer);
+    recursive = FALSE;
+}
+
 /*
  * Close window "win" in tab page "tp", which is not the current tab page.
  * This may be the last window in that tab page and result in closing the tab,
@@ -2731,6 +2753,12 @@ win_close_othertab(win_T *win, int free_buf, tabpage_T *tp)
 					       && win->w_buffer->b_locked > 0))
 	return; // window is already being closed
 
+    // Trigger WinClosed just before starting to free window-related resources.
+    trigger_winclosed(win);
+    // autocmd may have freed the window already.
+    if (!win_valid_any_tab(win))
+	return;
+
     if (win->w_buffer != NULL)
 	// Close the link to the buffer.
 	close_buffer(win, win->w_buffer, free_buf ? DOBUF_UNLOAD : 0,