refactor(statusline): set 'statusline' once (and not update on events)

Details:
- Setting targeted window-local values of 'statusline' on appropriate
  events is (on paper) better for performance. However, this introduces
  issues when those targeted events don't trigger (like `noautocmd` with
  floating windows). Although blocking important events is more or less
  a fault of what's blocking them, working around various issues doesn't
  really worth a performance boost.

  Instead set 'statusline' option once globally to a Vimscript value
  which will dynamically decide which content (active or inactive) to
  show. The computation overhead is pretty minimal (around 0.13
  microseconds for every 'statusline' evaluation) but the increase in
  robustness seems to be worth it (as now type of content will be
  decided just at the time when it is needed).

  This is made possible by a deeply hidden `g:actual_curwin` variable
  which is set during `%{%...%}` statusline evaluation specifically for
  this reason (to be able for the statusline to be both evaluated inside
  its target window and decide if that target is actually current).

lua/mini/statusline.lua

@@ -177,14 +177,12 @@ MiniStatusline.config = {
 --- Compute content for active window
 MiniStatusline.active = function()
   if H.is_disabled() then return '' end
-
   return (H.get_config().content.active or H.default_content_active)()
 end
 
 --- Compute content for inactive window
 MiniStatusline.inactive = function()
   if H.is_disabled() then return '' end
-
   return (H.get_config().content.inactive or H.default_content_inactive)()
 end
 
@@ -506,12 +504,9 @@ H.apply_config = function(config)
   -- Set settings to ensure statusline is displayed properly
   if config.set_vim_settings and (vim.o.laststatus == 0 or vim.o.laststatus == 1) then vim.o.laststatus = 2 end
 
-  -- Ensure proper 'statusline' values (to not rely on autocommands trigger)
-  H.ensure_content()
-
-  -- Set global value to reduce flickering when first time entering buffer, as
-  -- it is used by default before content is ensured on next loop
-  vim.go.statusline = '%{%v:lua.MiniStatusline.active()%}'
+  -- Set statusline globally and dynamically decide which content to use
+  vim.go.statusline =
+    '%{%(nvim_get_current_win()==#g:actual_curwin || &laststatus==3) ? v:lua.MiniStatusline.active() : v:lua.MiniStatusline.inactive()%}'
 end
 
 H.create_autocommands = function()
@@ -521,8 +516,6 @@ H.create_autocommands = function()
     vim.api.nvim_create_autocmd(event, { group = gr, pattern = pattern, callback = callback, desc = desc })
   end
 
-  au({ 'WinEnter', 'BufWinEnter' }, '*', H.ensure_content, 'Ensure statusline content')
-
   -- Use `schedule_wrap()` because at `LspDetach` server is still present
   local track_lsp = vim.schedule_wrap(function(data)
     H.attached_lsp[data.buf] = vim.api.nvim_buf_is_valid(data.buf) and H.compute_attached_lsp(data.buf) or nil
@@ -567,17 +560,6 @@ H.get_config = function(config)
   return vim.tbl_deep_extend('force', MiniStatusline.config, vim.b.ministatusline_config or {}, config or {})
 end
 
--- Content --------------------------------------------------------------------
-H.ensure_content = vim.schedule_wrap(function()
-  -- NOTE: Use `schedule_wrap()` to properly work inside autocommands because
-  -- they might temporarily change current window
-  local cur_win_id, is_global_stl = vim.api.nvim_get_current_win(), vim.o.laststatus == 3
-  for _, win_id in ipairs(vim.api.nvim_list_wins()) do
-    vim.wo[win_id].statusline = (win_id == cur_win_id or is_global_stl) and '%{%v:lua.MiniStatusline.active()%}'
-      or '%{%v:lua.MiniStatusline.inactive()%}'
-  end
-end)
-
 -- Mode -----------------------------------------------------------------------
 -- Custom `^V` and `^S` symbols to make this file appropriate for copy-paste
 -- (otherwise those symbols are not displayed).

tests/test_statusline.lua

@@ -116,7 +116,10 @@ T['setup()']['creates side effects'] = function()
   has_highlight('MiniStatuslineInactive', 'links to StatusLineNC')
 
   -- Sets global value of 'statusline'
-  eq(child.go.statusline, '%{%v:lua.MiniStatusline.active()%}')
+  eq(
+    child.go.statusline,
+    '%{%(nvim_get_current_win()==#g:actual_curwin || &laststatus==3) ? v:lua.MiniStatusline.active() : v:lua.MiniStatusline.inactive()%}'
+  )
 end
 
 T['setup()']['creates `config` field'] = function()