feat: nvim: treesitter: enable code folding

nix/base-system/init.lua

@@ -43,6 +43,23 @@ vim.api.nvim_create_autocmd({ "BufEnter", "BufWinEnter" }, {
     end,
 })
 
+vim.api.nvim_create_autocmd({ "BufNewfile", "BufRead" }, {
+    callback = function(args)
+        -- If treesitter supports this filetype then use the treesitter fold expression
+        local ft = vim.bo.filetype
+        if ft and ft ~= "" then
+            -- Safely check if a parser exists for this filetype
+            local has_parser = pcall(function() return vim.treesitter.language.inspect(ft) end)
+            if has_parser then
+                vim.wo.foldexpr = 'v:lua.vim.treesitter.foldexpr()'
+                vim.wo.foldmethod = 'expr'
+                vim.wo.foldlevel = 3
+            end
+        end
+    end,
+})
+
+
 vim.cmd([[
 au BufNewFile,BufRead *Makefile,*.mk set noexpandtab
 ]])
@@ -320,6 +337,7 @@ require('nvim-treesitter.configs').setup {
         extended_mode = true,
         max_file_lines = nil,
     },
+    textobjects = { enable = true },
     incremental_selection = {
       enable = true,
       keymaps = {