vim: Move neovim version check and deprecation warning to init.lua (#36)

init.lua would be a better place than vimrc because it's specific to
neovim. Also, allow users to suppress this startup deprecation warning
message by setting `DOTFILES_SUPPRESS_NEOVIM_VERSION_WARNING=1`.

nvim/init.lua

@@ -47,6 +47,19 @@ if vim.fn.has('nvim-0.7') == 0 then
     echohl WarningMsg | echom 'This version of neovim is unsupported. Please upgrade to Neovim 0.7.0+ or higher.' | echohl None
   ]]
   return
+
+elseif vim.fn.has('nvim-0.8.0') == 0 then
+  vim.defer_fn(function()
+    local like_false = function(x) return x == nil or x == "0" or x == "" end
+    if not like_false(vim.env.DOTFILES_SUPPRESS_NEOVIM_VERSION_WARNING) then return end
+    local msg = 'Please upgrade to latest neovim (0.9.0+).\n'
+    msg = msg .. 'Support for neovim < 0.8 will be dropped soon.'
+    msg = msg .. '\n\n' .. string.format('Try: $ %s install neovim', vim.fn.has('mac') > 0 and 'brew' or 'dotfiles')
+    msg = msg .. '\n\n' .. ('If you cannot upgrade yet but want to suppress this warning,\n'
+                            .. 'use `export DOTFILES_SUPPRESS_NEOVIM_VERSION_WARNING=1`.')
+    ---@diagnostic disable-next-line: param-type-mismatch
+    vim.notify(msg, 'error', { title = 'Deprecation Warning', timeout = 5000 })
+  end, 100)
 end
 
 -- require a lua module, but force reload it (RC files can be re-sourced)

vim/vimrc

@@ -14,18 +14,6 @@ else  " No timer support, this will run during VimEnter (before UI draws)
   autocmd! VimEnter * call execute('doautocmd User LazyInit')
 endif
 
-" Check neovim version.
-if has('nvim') && !has('nvim-0.8.0')
-  let s:warning_msg = 'Please upgrade to latest neovim (0.9.0+). Support for neovim < 0.8 will be dropped soon. '
-  let s:warning_msg .= printf('(Try: %s install neovim)', has('mac') ? 'brew' : 'dotfiles')
-  if exists('*luaeval')
-    autocmd VimEnter * call timer_start(100, { ->
-          \ luaeval("vim.notify(_A[1], _A[2], _A[3])", [s:warning_msg, 'error', {'title': 'Deprecation Warning'}])
-          \ })
-  else
-    autocmd VimEnter * echohl WarningMsg | echom s:warning_msg | echohl None
-  endif
-endif
 
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 " 0. Load Plugin {{{