babel-core: add options for different parser/generator (#3561)

* babel-core: add options for different parser/generator

* test for experiemental plugins, other babylon options

* fix passing options into parser

* Fix when no code is provided

* fixup tests

* fix tests again

* use filename and fallback to cwd

packages/babel-generator/src/index.js

@@ -93,6 +93,11 @@ function normalizeOptions(code, opts, tokens): Format {
  * Determine if input code uses more single or double quotes.
  */
 function findCommonStringDelimiter(code, tokens) {
+  const DEFAULT_STRING_DELIMITER = "double";
+  if (!code) {
+    return DEFAULT_STRING_DELIMITER;
+  }
+
   let occurences = {
     single: 0,
     double: 0
@@ -117,7 +122,7 @@ function findCommonStringDelimiter(code, tokens) {
   if (occurences.single > occurences.double) {
     return "single";
   } else {
-    return "double";
+    return DEFAULT_STRING_DELIMITER;
   }
 }