Handle synchronous errors in `worker.transformCode`

Summary: `worker.transformCode` is a callback-taking function, but did not properly guard against errors thrown in its body.

Reviewed By: cpojer

Differential Revision: D5245253

fbshipit-source-id: 3fd08b68dd8605f664b316652ebd1f9497b2dac9

packages/metro-bundler/src/JSTransformer/worker/__tests__/worker-test.js

@@ -213,6 +213,24 @@ describe('code transformation worker:', () => {
         },
       );
     });
+
+    it('calls back with every error thrown by `extractDependencies`', done => {
+      const error = new Error('arbitrary');
+      extractDependencies.mockImplementation(() => {
+        throw error;
+      });
+      transformCode(
+        transformer,
+        'arbitrary.js',
+        'local/arbitrary.js',
+        'code',
+        {},
+        (e, data) => {
+          expect(e).toBe(error);
+          done();
+        },
+      );
+    });
   });
 
   describe('Minifications:', () => {

packages/metro-bundler/src/JSTransformer/worker/index.js

@@ -12,6 +12,7 @@
 
 'use strict';
 
+const asyncify = require('async/asyncify');
 const constantFolding = require('./constant-folding');
 const extractDependencies = require('./extract-dependencies');
 const inline = require('./inline');
@@ -73,15 +74,23 @@ export type Data = {
 };
 
 type Callback<T> = (error: ?Error, data: ?T) => mixed;
+type TransformCode = (
+  Transformer<*>,
+  string,
+  LocalPath,
+  string,
+  Options,
+  Callback<Data>,
+) => void;
 
-function transformCode(
+const transformCode: TransformCode = asyncify(
+  (
     transformer: Transformer<*>,
     filename: string,
     localPath: LocalPath,
     sourceCode: string,
     options: Options,
-  callback: Callback<Data>,
+  ): Data => {
-) {
     invariant(
       !options.minify || options.transform.generateSourceMaps,
       'Minifying source code requires the `generateSourceMaps` option to be `true`',
@@ -100,18 +109,12 @@ function transformCode(
       start_timestamp: process.hrtime(),
     };
 
-  let transformed;
+    const transformed = transformer.transform({
-  try {
-    transformed = transformer.transform({
       filename,
       localPath,
       options: options.transform,
       src: sourceCode,
     });
-  } catch (error) {
-    callback(error);
-    return;
-  }
 
     invariant(
       transformed != null,
@@ -140,7 +143,9 @@ function transformCode(
       ? {dependencies: [], dependencyOffsets: []}
       : extractDependencies(code);
 
-  const timeDelta = process.hrtime(transformFileStartLogEntry.start_timestamp);
+    const timeDelta = process.hrtime(
+      transformFileStartLogEntry.start_timestamp,
+    );
     const duration_ms = Math.round((timeDelta[0] * 1e9 + timeDelta[1]) / 1e6);
     const transformFileEndLogEntry = {
       action_name: 'Transforming file',
@@ -150,12 +155,13 @@ function transformCode(
       log_entry_label: 'Transforming file',
     };
 
-  callback(null, {
+    return {
       result: {...depsResult, code, map},
       transformFileStartLogEntry,
       transformFileEndLogEntry,
-  });
+    };
-}
+  },
+);
 
 exports.transformAndExtractDependencies = (
   transform: string,