Improve serializability check & error message

Author: davidtaylorhq

packages/babel/src/index.js

@@ -102,22 +102,26 @@ const returnObject = () => {
   return {};
 };
 
-function isSerializable(value) {
-  if (value === null) {
-    return true;
-  } else if (Array.isArray(value)) {
-    return value.every(isSerializable);
-  }
-  switch (typeof value) {
-    case 'string':
-    case 'number':
-    case 'boolean':
-      return true;
-    case 'object':
-      return Object.keys(value).every((key) => isSerializable(value[key]));
-    default:
-      return false;
+function findNonSerializableOption(obj) {
+  const isSerializable = (value) => {
+    if (value === null) return true;
+    if (Array.isArray(value)) return value.every(isSerializable);
+    switch (typeof value) {
+      case 'string':
+      case 'number':
+      case 'boolean':
+        return true;
+      case 'object':
+        return Object.values(value).every(isSerializable);
+      default:
+        return false;
+    }
+  };
+
+  for (const key of Object.keys(obj)) {
+    if (!isSerializable(obj[key])) return key;
   }
+  return null;
 }
 
 function createBabelInputPluginFactory(customCallback = returnObject) {
@@ -159,12 +163,16 @@ function createBabelInputPluginFactory(customCallback = returnObject) {
     }
 
     if (parallel) {
-      const parallelAllowed =
-        isSerializable(babelOptions) && !overrides?.config && !overrides?.result;
-
-      if (!parallelAllowed) {
+      if (overrides?.config) {
+        throw new Error('Cannot use "parallel" mode with a custom "config" override.');
+      }
+      if (overrides?.result) {
+        throw new Error('Cannot use "parallel" mode with a custom "result" override.');
+      }
+      const nonSerializableKey = findNonSerializableOption(babelOptions);
+      if (nonSerializableKey) {
         throw new Error(
-          'Cannot use "parallel" mode alongside custom overrides or non-serializable Babel options.'
+          `Cannot use "parallel" mode because the "${nonSerializableKey}" option is not serializable.`
         );
       }
 

packages/babel/test/as-input-plugin.mjs

@@ -655,9 +655,7 @@ test('throws when using parallel with non-serializable babel options', async ()
         }
       ]
     })
-  ).rejects.toThrow(
-    /Cannot use "parallel" mode alongside custom overrides or non-serializable Babel options/
-  );
+  ).rejects.toThrow(/Cannot use "parallel" mode because the "plugins" option is not serializable/);
 });
 
 test('throws when using parallel with config override', () => {
@@ -670,7 +668,7 @@ test('throws when using parallel with config override', () => {
   });
 
   expect(() => customBabelPlugin({ babelHelpers: 'bundled', parallel: true })).toThrow(
-    /Cannot use "parallel" mode alongside custom overrides or non-serializable Babel options/
+    /Cannot use "parallel" mode with a custom "config" override/
   );
 });
 
@@ -684,6 +682,6 @@ test('throws when using parallel with result override', () => {
   });
 
   expect(() => customBabelPlugin({ babelHelpers: 'bundled', parallel: true })).toThrow(
-    /Cannot use "parallel" mode alongside custom overrides or non-serializable Babel options/
+    /Cannot use "parallel" mode with a custom "result" override/
   );
 });