add support of multiline string

lib.nix

@@ -16,7 +16,7 @@
  */
 let
   inherit (builtins) isString isFloat isInt isBool isList isAttrs isNull isPath;
-  inherit (builtins) concatStringsSep filter mapAttrs attrValues concatLists;
+  inherit (builtins) concatStringsSep filter mapAttrs attrValues concatLists match;
 
   isNotNull = v: !(isNull v);
   excludeNull = expr: filter isNotNull expr;
@@ -175,7 +175,10 @@ let
 
   toLuaBool = expr: if expr then "true" else "false";
   toLuaNumber = toString;
-  toLuaString = expr: "\"${validString expr}\"";
+  toLuaString = expr:
+    let str = validString expr; in
+    let isLines = match ".*\n.*" str; in
+    if isLines != null then "[[\n${str}]]" else "\"${str}\"";
   toLuaList = onValue: expr:
     let
       wrapObj = expr: "{ ${concatStringsSep ", " expr} }";

lib.test.nix

@@ -35,6 +35,17 @@ with nix2lua; pkgs.lib.runTests {
     expr = toLua "hello world";
     expected = ''"hello world"'';
   };
+  "test returns a multiline lua string" = {
+    expr = toLua ''
+      hello
+      world
+    '';
+    expected = ''
+      [[
+      hello
+      world
+      ]]'';
+  };
   "test returns a path as a lua string" = {
     expr = toLua /hello/world;
     expected = ''"/hello/world"'';