vim-patch:8.2.3591: no event is triggered when closing a window (#16306)

Problem:    No event is triggered when closing a window.
Solution:   Add the WinClosed event. (Naohiro Ono, closes vim/vim#9110)
23beefed73

Nvim has already implemented this feature, so this only changes tests
and docs.

runtime/doc/autocmd.txt

@@ -1002,8 +1002,9 @@ VimResume			After Nvim resumes from |suspend| state.
 							*VimSuspend*
 VimSuspend			Before Nvim enters |suspend| state.
 							*WinClosed*
-WinClosed			After closing a window. <afile> expands to the
-				|window-ID|.
+WinClosed			After closing a window.  The pattern is
+				matched against the |window-ID|.  Both
+				<amatch> and <afile> are set to the |window-ID|.
 				After WinLeave.
 				Non-recursive (event cannot trigger itself).
 				See also |ExitPre|, |QuitPre|.

runtime/doc/vim_diff.txt

@@ -186,7 +186,6 @@ Events:
   |TermOpen|
   |UIEnter|
   |UILeave|
-  |WinClosed|
 
 Functions:
   |dictwatcheradd()| notifies a callback whenever a |Dict| is modified

src/nvim/testdir/test_autocmd.vim

@@ -222,6 +222,7 @@ 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')
@@ -238,8 +239,8 @@ 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 = []
@@ -250,7 +251,7 @@ 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
@@ -259,6 +260,45 @@ 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'