Auto install treesitter parsers when opening a file

closes nvim-lua#1951

Author: oriori1703

init.lua

@@ -1200,7 +1200,18 @@ require('lazy').setup({
           local language = vim.treesitter.language.get_lang(filetype)
           if not language then return end
 
-          treesitter_try_attach(buf, language)
+          local installed_parsers = require('nvim-treesitter').get_installed 'parsers'
+
+          if vim.tbl_contains(installed_parsers, language) then
+            -- enable the parser if it is installed
+            treesitter_try_attach(buf, language)
+          elseif vim.tbl_contains(available_parsers, language) then
+            -- if a parser is available in `nvim-treesitter` auto install it, and enable it after the installation is done
+            require('nvim-treesitter').install(language):await(function() treesitter_try_attach(buf, language) end)
+          else
+            -- try to enable treesitter features in case the parser exists but is not available from `nvim-treesitter`
+            treesitter_try_attach(buf, language)
+          end
         end,
       })
     end,