tests: optionally enable treesitter-parsers for json,jsonc,lua.

(enabling lua is most likely a nop, since it is already available by
default in newer neovim-versions)

tests/helpers.lua

@@ -31,6 +31,12 @@ function M.session_setup_luasnip(opts)
 		or false
 	local setup_extend = opts.setup_extend ~= nil and opts.setup_extend
 		or {}
+	local setup_parsers
+	if opts.setup_parsers ~= nil then
+		setup_parsers = opts.setup_parsers
+	else
+		setup_parsers = false
+	end
 
 	-- stylua: ignore
 	helpers.exec("set rtp+=" .. os.getenv("LUASNIP_SOURCE"))
@@ -41,6 +47,25 @@ function M.session_setup_luasnip(opts)
 		("luafile %s/plugin/luasnip.lua"):format(os.getenv("LUASNIP_SOURCE"))
 	)
 
+	if setup_parsers then
+		-- adding the lua-parser, is either a nop or adds the parser on
+		-- versions where it does not exist by default.
+		exec_lua[[
+			ts_lang_add =
+				(vim.treesitter.language and vim.treesitter.language.add)
+				and function(lang, path)
+						vim.treesitter.language.add(lang, {path = path})
+					end
+				or vim.treesitter.require_language
+
+			-- this is a nop on new versions of neovim, where the lua-parser is shipped by default.
+			ts_lang_add("lua", os.getenv("LUASNIP_SOURCE") .. "/tests/parsers/lua.so")
+
+			ts_lang_add("json", os.getenv("LUASNIP_SOURCE") .. "/tests/parsers/json.so")
+			ts_lang_add("jsonc", os.getenv("LUASNIP_SOURCE") .. "/tests/parsers/jsonc.so")
+		]]
+	end
+
 	helpers.exec_lua([[
 		-- MYVIMRC might not be set when nvim is loaded like this.
 		vim.env.MYVIMRC = "/.vimrc"
@@ -49,7 +74,9 @@ function M.session_setup_luasnip(opts)
 		ls.setup(vim.tbl_extend("force", {
 			store_selection_keys = "<Tab>"
 		}, ...))
-	]], setup_extend)
+	]],
+		setup_extend
+	)
 
 	if not no_snip_globals then
 		helpers.exec_lua([[