feat(win): make split window "stacking" configurable

lua/snacks/win.lua

@@ -83,6 +83,7 @@ M.meta = {
 ---@field text? string|string[]|fun():(string[]|string) Initial lines to set in the buffer
 ---@field actions? table<string, snacks.win.Action.spec> Actions that can be used in key mappings
 ---@field resize? boolean Automatically resize the window when the editor is resized
+---@field stack? boolean When enabled, multiple split windows with the same position will be stacked together (useful for terminals)
 local defaults = {
   show = true,
   fixbuf = true,
@@ -701,15 +702,18 @@ function M:open_win()
   elseif position == "current" then
     self.win = vim.api.nvim_get_current_win()
     vim.api.nvim_win_set_buf(self.win, self.buf)
-  else
+  else --split
     local parent = self.opts.win and vim.api.nvim_win_is_valid(self.opts.win) and self.opts.win or 0
     local vertical = position == "left" or position == "right"
-    if parent == 0 then
+    -- When stacking is enabled, find an existing window with the same relative/position
+    -- and stack the new window perpendicular to it instead of creating a new split
+    if parent == 0 and self.opts.stack then
       for _, win in ipairs(vim.api.nvim_tabpage_list_wins(0)) do
         if
           vim.w[win].snacks_win
           and vim.w[win].snacks_win.relative == relative
           and vim.w[win].snacks_win.position == position
+          and vim.w[win].snacks_win.stack == true
         then
           parent = win
           relative = "win"
@@ -737,6 +741,7 @@ function M:open_win()
     id = self.id,
     position = self.opts.position,
     relative = self.opts.relative,
+    stack = self.opts.stack,
   }
 end