vim-patch:8.2.0991: cannot get window type for autocmd and preview window

Problem:    Cannot get window type for autocmd and preview window.
Solution:   Add types to win_gettype(). (Yegappan Lakshmanan, closes vim/vim#6277)
0fe937fd86

Cherry-pick test_preview.vim,test_window_cmd.vim changes
from patch v8.2.0522.

runtime/doc/eval.txt

@@ -9280,7 +9280,10 @@ win_getid([{win} [, {tab}]])				*win_getid()*
 
 win_gettype([{nr}])					*win_gettype()*
 		Return the type of the window:
+			"aucmdwin"	autocommand window. Temporary window
+					used to execute autocommands.
 			"popup"		popup window |popup|
+			"preview"	preview window |preview-window|
 			"command"	command-line window |cmdwin|
 			(empty)		normal window
 			"unknown"	window {nr} not found

src/nvim/eval/funcs.c

@@ -11006,7 +11006,11 @@ static void f_win_gettype(typval_T *argvars, typval_T *rettv, FunPtr fptr)
       return;
     }
   }
-  if (wp->w_floating) {
+  if (wp == aucmd_win) {
+    rettv->vval.v_string = vim_strsave((char_u *)"aucmdwin");
+  } else if (wp->w_p_pvw) {
+    rettv->vval.v_string = vim_strsave((char_u *)"preview");
+  } else if (wp->w_floating) {
     rettv->vval.v_string = vim_strsave((char_u *)"popup");
   } else if (wp == curwin && cmdwin_type != 0) {
     rettv->vval.v_string = vim_strsave((char_u *)"command");

src/nvim/testdir/test_autocmd.vim

@@ -1934,4 +1934,26 @@ func Test_autocmd_sigusr1()
   unlet g:sigusr1_passed
 endfunc
 
+" Test for the temporary internal window used to execute autocmds
+func Test_autocmd_window()
+  %bw!
+  edit one.txt
+  tabnew two.txt
+  let g:blist = []
+  augroup aucmd_win_test
+    au!
+    au BufEnter * call add(g:blist, [expand('<afile>'),
+          \ win_gettype(bufwinnr(expand('<afile>')))])
+  augroup END
+
+  doautoall BufEnter
+  call assert_equal([['one.txt', 'aucmdwin'], ['two.txt', '']], g:blist)
+
+  augroup aucmd_win_test
+    au!
+  augroup END
+  augroup! aucmd_win_test
+  %bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/nvim/testdir/test_preview.vim

@@ -11,3 +11,47 @@ func Test_Psearch()
   call assert_equal(wincount, winnr('$'))
   bwipe
 endfunc
+
+func Test_window_preview()
+  " Open a preview window
+  pedit Xa
+  call assert_equal(2, winnr('$'))
+  call assert_equal(0, &previewwindow)
+
+  " Go to the preview window
+  wincmd P
+  call assert_equal(1, &previewwindow)
+  call assert_equal('preview', win_gettype())
+
+  " Close preview window
+  wincmd z
+  call assert_equal(1, winnr('$'))
+  call assert_equal(0, &previewwindow)
+
+  call assert_fails('wincmd P', 'E441:')
+endfunc
+
+func Test_window_preview_from_help()
+  filetype on
+  call writefile(['/* some C code */'], 'Xpreview.c')
+  help
+  pedit Xpreview.c
+  wincmd P
+  call assert_equal(1, &previewwindow)
+  call assert_equal('c', &filetype)
+  wincmd z
+
+  filetype off
+  close
+  call delete('Xpreview.c')
+endfunc
+
+func Test_multiple_preview_windows()
+  new
+  set previewwindow
+  new
+  call assert_fails('set previewwindow', 'E590:')
+  %bw!
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab

src/nvim/testdir/test_window_cmd.vim

@@ -172,39 +172,6 @@ func Test_window_split_edit_bufnr()
   %bw!
 endfunc
 
-func Test_window_preview()
-  " Open a preview window
-  pedit Xa
-  call assert_equal(2, winnr('$'))
-  call assert_equal(0, &previewwindow)
-
-  " Go to the preview window
-  wincmd P
-  call assert_equal(1, &previewwindow)
-
-  " Close preview window
-  wincmd z
-  call assert_equal(1, winnr('$'))
-  call assert_equal(0, &previewwindow)
-
-  call assert_fails('wincmd P', 'E441:')
-endfunc
-
-func Test_window_preview_from_help()
-  filetype on
-  call writefile(['/* some C code */'], 'Xpreview.c')
-  help
-  pedit Xpreview.c
-  wincmd P
-  call assert_equal(1, &previewwindow)
-  call assert_equal('c', &filetype)
-  wincmd z
-
-  filetype off
-  close
-  call delete('Xpreview.c')
-endfunc
-
 func Test_window_exchange()
   e Xa