patch 9.1.0059: No event triggered before creating a window

Problem:  No event is triggered before creating a window.
          (Sergey Vlasov)
Solution: Add the WinNewPre event (Sergey Vlasov)

fixes: #10635
closes: #12761

Signed-off-by: Sergey Vlasov <sergey@vlasov.me>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/autocmd.txt

@@ -1,4 +1,4 @@
-*autocmd.txt*   For Vim version 9.1.  Last change: 2024 Jan 23
+*autocmd.txt*   For Vim version 9.1.  Last change: 2024 Jan 25
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -381,6 +381,7 @@ Name			triggered by ~
 |CursorMoved|		the cursor was moved in Normal mode
 |CursorMovedI|		the cursor was moved in Insert mode
 
+|WinNewPre|		before creating a new window
 |WinNew|		after creating a new window
 |TabNew|		after creating a new tab page
 |WinClosed|		after closing a window
@@ -1390,6 +1391,18 @@ WinLeave			Before leaving a window.  If the window to be
 				WinLeave autocommands (but not for ":new").
 				Not used for ":qa" or ":q" when exiting Vim.
 
+							*WinNewPre*
+WinNewPre			Before creating a new window. Triggered
+				before commands that modify window layout by
+				creating a split or new tab page. Not done for
+				the first window, when Vim has just started.
+				It is not allowed to modify window layout
+				while executing commands for the WinNewPre
+				event.
+				Most useful to store current window layout
+				and compare it with the new layout after the
+				Window has been created.
+
 							*WinNew*
 WinNew				When a new window was created.  Not done for
 				the first window, when Vim has just started.

runtime/doc/tags

@@ -5785,6 +5785,7 @@ WinClosed	autocmd.txt	/*WinClosed*
 WinEnter	autocmd.txt	/*WinEnter*
 WinLeave	autocmd.txt	/*WinLeave*
 WinNew	autocmd.txt	/*WinNew*
+WinNewPre	autocmd.txt	/*WinNewPre*
 WinResized	autocmd.txt	/*WinResized*
 WinResized-event	windows.txt	/*WinResized-event*
 WinScrolled	autocmd.txt	/*WinScrolled*

runtime/doc/todo.txt

@@ -4667,7 +4667,6 @@ GUI:
 
 
 Autocommands:
-9   Add WinNewPre - before creating a new window. #10635
 9   When triggering WinNew provide the window ID somehow.  #10633
 9   Rework the code from FEAT_OSFILETYPE for autocmd-osfiletypes to use
     'filetype'.  Only for when the current buffer is known.

runtime/syntax/vim.vim

@@ -11,6 +11,7 @@
 " 	2024 Jan 14 by Vim Project (TermResponseAll autocommand)
 " 	2024 Jan 15 by Vim Project (:hi ctermfont attribute)
 " 	2024 Jan 23 by Vim Project (add :[23]match commands)
+" 	2024 Jan 25 by Vim Project (WinNewPre autocommand)
 " Version:	9.0-25
 " URL:	http://www.drchip.org/astronaut/vim/index.html#SYNTAX_VIM
 " Automatically generated keyword lists: {{{1
@@ -76,7 +77,7 @@ syn keyword vimErrSetting contained	bioskey biosk conskey consk autoprint beauti
 
 " AutoCmd Events {{{2
 syn case ignore
-syn keyword vimAutoEvent contained	BufAdd BufDelete BufFilePost BufHidden BufNew BufRead BufReadPost BufUnload BufWinLeave BufWrite BufWritePost CmdlineChanged CmdlineLeave CmdwinEnter ColorScheme CompleteChanged CompleteDonePre CursorHoldI CursorMovedI DiffUpdated DirChanged DirChangedPre EncodingChanged ExitPre FileAppendCmd FileAppendPost FileAppendPre FileChangedRO FileChangedShell FileChangedShellPost FileEncoding FileExplorer FileReadCmd FileReadPost FileReadPre FileType FileWriteCmd FileWritePost FileWritePre FilterReadPost FilterReadPre FilterWritePost FilterWritePre FocusGained FocusLost FuncUndefined GUIEnter GUIFailed InsertChange InsertCharPre InsertEnter InsertLeave InsertLeavePre MenuPopup ModeChanged OptionSet QuickFixCmdPost QuickFixCmdPre QuitPre RemoteReply SafeState SafeStateAgain SessionLoadPost ShellCmdPost ShellFilterPost SigUSR1 SourceCmd SourcePost SourcePre SpellFileMissing StdinReadPost StdinReadPre SwapExists Syntax TabClosed TabEnter TabLeave TabNew TermChanged TerminalOpen TerminalWinOpen TermResponse TermResponseAll TextChanged TextChangedI TextChangedP TextChangedT TextYankPost User VimEnter VimLeave VimLeavePre VimResized VimResume VimSuspend WinClosed WinEnter WinLeave WinNew WinResized WinScrolled
+syn keyword vimAutoEvent contained	BufAdd BufDelete BufFilePost BufHidden BufNew BufRead BufReadPost BufUnload BufWinLeave BufWrite BufWritePost CmdlineChanged CmdlineLeave CmdwinEnter ColorScheme CompleteChanged CompleteDonePre CursorHoldI CursorMovedI DiffUpdated DirChanged DirChangedPre EncodingChanged ExitPre FileAppendCmd FileAppendPost FileAppendPre FileChangedRO FileChangedShell FileChangedShellPost FileEncoding FileExplorer FileReadCmd FileReadPost FileReadPre FileType FileWriteCmd FileWritePost FileWritePre FilterReadPost FilterReadPre FilterWritePost FilterWritePre FocusGained FocusLost FuncUndefined GUIEnter GUIFailed InsertChange InsertCharPre InsertEnter InsertLeave InsertLeavePre MenuPopup ModeChanged OptionSet QuickFixCmdPost QuickFixCmdPre QuitPre RemoteReply SafeState SafeStateAgain SessionLoadPost ShellCmdPost ShellFilterPost SigUSR1 SourceCmd SourcePost SourcePre SpellFileMissing StdinReadPost StdinReadPre SwapExists Syntax TabClosed TabEnter TabLeave TabNew TermChanged TerminalOpen TerminalWinOpen TermResponse TermResponseAll TextChanged TextChangedI TextChangedP TextChangedT TextYankPost User VimEnter VimLeave VimLeavePre VimResized VimResume VimSuspend WinClosed WinEnter WinLeave WinNewPre WinNew WinResized WinScrolled
 syn keyword vimAutoEvent contained	BufCreate BufEnter BufFilePre BufLeave BufNewFile BufReadCmd BufReadPre BufWinEnter BufWipeout BufWriteCmd BufWritePre CmdlineEnter CmdUndefined CmdwinLeave ColorSchemePre CompleteDone CursorHold CursorMoved
 
 " Highlight commonly used Groupnames {{{2

src/autocmd.c

@@ -188,6 +188,7 @@ static struct event_name
     {"VimEnter",	EVENT_VIMENTER},
     {"VimLeave",	EVENT_VIMLEAVE},
     {"VimLeavePre",	EVENT_VIMLEAVEPRE},
+    {"WinNewPre",	EVENT_WINNEWPRE},
     {"WinNew",		EVENT_WINNEW},
     {"WinClosed",	EVENT_WINCLOSED},
     {"WinEnter",	EVENT_WINENTER},

src/testdir/test_autocmd.vim

@@ -270,6 +270,7 @@ func Test_win_tab_autocmd()
   let g:record = []
 
   augroup testing
+    au WinNewPre * call add(g:record, 'WinNewPre')
     au WinNew * call add(g:record, 'WinNew')
     au WinClosed * call add(g:record, 'WinClosed')
     au WinEnter * call add(g:record, 'WinEnter')
@@ -286,8 +287,8 @@ func Test_win_tab_autocmd()
   close
 
   call assert_equal([
-	\ 'WinLeave', 'WinNew', 'WinEnter',
+	\ 'WinNewPre', 'WinLeave', 'WinNew', 'WinEnter',
-	\ 'WinLeave', 'TabLeave', 'WinNew', 'WinEnter', 'TabNew', 'TabEnter',
+	\ 'WinLeave', 'TabLeave', 'WinNewPre', 'WinNew', 'WinEnter', 'TabNew', 'TabEnter',
 	\ 'WinLeave', 'TabLeave', 'WinClosed', 'TabClosed', 'WinEnter', 'TabEnter',
 	\ 'WinLeave', 'WinClosed', 'WinEnter'
 	\ ], g:record)
@@ -298,17 +299,96 @@ func Test_win_tab_autocmd()
   bwipe somefile
 
   call assert_equal([
-	\ 'WinLeave', 'TabLeave', 'WinNew', 'WinEnter', 'TabNew', 'TabEnter',
+	\ 'WinLeave', 'TabLeave', 'WinNewPre', 'WinNew', 'WinEnter', 'TabNew', 'TabEnter',
 	\ 'WinLeave', 'TabLeave', 'WinEnter', 'TabEnter',
 	\ 'WinClosed', 'TabClosed'
 	\ ], g:record)
 
+  let g:record = []
+  copen
+  help
+  tabnext
+  vnew
+
+  call assert_equal([
+	\ 'WinNewPre', 'WinLeave', 'WinNew', 'WinEnter',
+	\ 'WinNewPre', 'WinLeave', 'WinNew', 'WinEnter',
+	\ 'WinNewPre', 'WinLeave', 'WinNew', 'WinEnter'
+	\ ], g:record)
+
   augroup testing
     au!
   augroup END
   unlet g:record
 endfunc
 
+func Test_WinNewPre()
+  " Test that the old window layout can be accessed before a new window is created.
+  let g:layouts_pre = []
+  let g:layouts_post = []
+  augroup testing
+    au WinNewPre * call add(g:layouts_pre, winlayout())
+    au WinNew * call add(g:layouts_post, winlayout())
+  augroup END
+  split
+  call assert_notequal(g:layouts_pre[0], g:layouts_post[0])
+  split
+  call assert_equal(g:layouts_pre[1], g:layouts_post[0])
+  call assert_notequal(g:layouts_pre[1], g:layouts_post[1])
+  tabnew
+  call assert_notequal(g:layouts_pre[2], g:layouts_post[1])
+  call assert_notequal(g:layouts_pre[2], g:layouts_post[2])
+  augroup testing
+    au!
+  augroup END
+  unlet g:layouts_pre
+  unlet g:layouts_post
+
+  " Test modifying window layout during WinNewPre throws.
+  let g:caught = 0
+  augroup testing
+    au!
+    au WinNewPre * split
+  augroup END
+  try
+    vnew
+  catch
+    let g:caught += 1
+  endtry
+  augroup testing
+    au!
+    au WinNewPre * tabnew
+  augroup END
+  try
+    vnew
+  catch
+    let g:caught += 1
+  endtry
+  augroup testing
+    au!
+    au WinNewPre * close
+  augroup END
+  try
+    vnew
+  catch
+    let g:caught += 1
+  endtry
+  augroup testing
+    au!
+    au WinNewPre * tabclose
+  augroup END
+  try
+    vnew
+  catch
+    let g:caught += 1
+  endtry
+  call assert_equal(4, g:caught)
+  augroup testing
+    au!
+  augroup END
+  unlet g:caught
+endfunc
+
 func Test_WinResized()
   CheckRunVimInTerminal
 

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    59,
 /**/
     58,
 /**/

src/vim.h

@@ -1435,7 +1435,8 @@ enum auto_event
     EVENT_VIMRESIZED,		// after Vim window was resized
     EVENT_WINENTER,		// after entering a window
     EVENT_WINLEAVE,		// before leaving a window
-    EVENT_WINNEW,		// when entering a new window
+    EVENT_WINNEWPRE,		// before creating a new window
+    EVENT_WINNEW,		// after creating 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_winnewpre(void);
 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);
@@ -955,6 +956,8 @@ win_split_ins(
     // Do not redraw here, curwin->w_buffer may be invalid.
     ++RedrawingDisabled;
 
+    trigger_winnewpre();
+
     if (flags & WSP_TOP)
 	oldwin = firstwin;
     else if (flags & WSP_BOT)
@@ -2886,6 +2889,14 @@ win_close(win_T *win, int free_buf)
     return OK;
 }
 
+    static void
+trigger_winnewpre(void)
+{
+    window_layout_lock();
+    apply_autocmds(EVENT_WINNEWPRE, NULL, NULL, FALSE, NULL);
+    window_layout_unlock();
+}
+
     static void
 trigger_winclosed(win_T *win)
 {
@@ -4477,6 +4488,9 @@ win_new_tabpage(int after)
 
     newtp->tp_localdir = (tp->tp_localdir == NULL)
 				    ? NULL : vim_strsave(tp->tp_localdir);
+
+    trigger_winnewpre();
+
     // Create a new empty window.
     if (win_alloc_firstwin(tp->tp_curwin) == OK)
     {