BREAKING: metro transformers should only output AST

Reviewed By: jeanlauliac

Differential Revision: D6396416

fbshipit-source-id: e4c6f0c0feb1ac638dc13dd3eb400f1bc72b5d44

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

@@ -15,12 +15,14 @@ jest
   .mock('../constant-folding')
   .mock('../extract-dependencies')
   .mock('../inline')
-  .mock('../minify');
+  .mock('../minify')
+  .mock('babel-generator');
 
 const {objectContaining} = jasmine;
 
 describe('code transformation worker:', () => {
   let transformCode;
+  let babelGenerator;
 
   let extractDependencies, transformer;
   beforeEach(() => {
@@ -35,6 +37,13 @@ describe('code transformation worker:', () => {
         map: [],
       })),
     };
+
+    babelGenerator = require('babel-generator');
+
+    babelGenerator.default.mockReturnValue({
+      code: '',
+      map: [],
+    });
   });
 
   it('calls the transform with file name, source code, and transform options', function() {
@@ -90,6 +99,11 @@ describe('code transformation worker:', () => {
       map: [],
     };
 
+    babelGenerator.default.mockReturnValue({
+      code: 'some.other(code)',
+      map: [],
+    });
+
     const data = await transformCode(
       transformer,
       'filename',
@@ -104,6 +118,12 @@ describe('code transformation worker:', () => {
   it('removes the leading `module.exports` before returning if the file is a JSON file, even if minified', async () => {
     const code = '{a:1,b:2}';
     const filePath = 'arbitrary/file.json';
+
+    babelGenerator.default.mockReturnValue({
+      code: '{a:1,b:2}',
+      map: [],
+    });
+
     const data = await transformCode(transformer, filePath, filePath, code, {});
 
     expect(data.result.code).toEqual(code);
@@ -116,6 +136,11 @@ describe('code transformation worker:', () => {
     };
     const filePath = 'arbitrary/file.js';
 
+    babelGenerator.default.mockReturnValue({
+      code: `${shebang} \n arbitrary(code)`,
+      map: [],
+    });
+
     const data = await transformCode(
       transformer,
       filePath,
@@ -155,6 +180,11 @@ describe('code transformation worker:', () => {
     it('passes the transformed code the `extractDependencies`', async () => {
       const code = 'arbitrary(code)';
 
+      babelGenerator.default.mockReturnValue({
+        code: 'arbitrary(code)',
+        map: [],
+      });
+
       await transformCode(transformer, 'filename', 'local/filename', code, {});
 
       expect(extractDependencies).toBeCalledWith(code, 'filename');
@@ -182,6 +212,11 @@ describe('code transformation worker:', () => {
     it('does not extract requires of JSON files', async () => {
       const jsonStr = '{"arbitrary":"json"}';
 
+      babelGenerator.default.mockReturnValue({
+        code: '{"arbitrary":"json"}',
+        map: [],
+      });
+
       const data = await transformCode(
         transformer,
         'arbitrary.json',

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

@@ -46,9 +46,7 @@ export type TransformArgs<ExtraOptions: {}> = {|
 |};
 
 export type TransformResults = {
-  ast: ?Ast,
-  code: string,
-  map: ?MappingsMap | RawMappings,
+  ast: Ast,
 };
 
 export type Transform<ExtraOptions: {}> = (
@@ -126,22 +124,20 @@ async function transformCode(
     src: sourceCode,
   });
 
-  // If we receive AST from the transformer, serialize it into code/map.
-  const transformed = result.ast
-    ? generate(
-        result.ast,
-        {
-          code: false,
-          comments: false,
-          compact: false,
-          filename: localPath,
-          retainLines: false,
-          sourceFileName: filename,
-          sourceMaps: true,
-        },
-        sourceCode,
-      )
-    : {code: result.code, map: result.map};
+  // Serialize the AST received from the transformer.
+  const transformed = generate(
+    result.ast,
+    {
+      code: false,
+      comments: false,
+      compact: false,
+      filename: localPath,
+      retainLines: false,
+      sourceFileName: filename,
+      sourceMaps: true,
+    },
+    sourceCode,
+  );
 
   // If the transformer returns standard sourcemaps, we need to transform them
   // to rawMappings so we can process them correctly.

packages/metro-bundler/src/transformer.js

@@ -17,7 +17,6 @@ const babel = require('babel-core');
 const crypto = require('crypto');
 const externalHelpersPlugin = require('babel-plugin-external-helpers');
 const fs = require('fs');
-const generate = require('babel-generator').default;
 const inlineRequiresPlugin = require('babel-preset-fbjs/plugins/inline-requires');
 const json5 = require('json5');
 const makeHMRConfig = require('babel-preset-react-native/configs/hmr');
@@ -132,36 +131,9 @@ function transform({filename, options, src, plugins}: Params) {
 
   try {
     const babelConfig = buildBabelConfig(filename, options, plugins);
-    const {ast, ignored} = babel.transform(src, babelConfig);
+    const {ast} = babel.transform(src, babelConfig);
 
-    if (ignored) {
-      return {
-        ast: null,
-        code: src,
-        filename,
-        map: null,
-      };
-    } else {
-      const result = generate(
-        ast,
-        {
-          comments: false,
-          compact: false,
-          filename,
-          retainLines: !!options.retainLines,
-          sourceFileName: filename,
-          sourceMaps: true,
-        },
-        src,
-      );
-
-      return {
-        ast,
-        code: result.code,
-        filename,
-        map: options.generateSourceMaps ? result.map : result.rawMappings,
-      };
-    }
+    return {ast};
   } finally {
     process.env.BABEL_ENV = OLD_BABEL_ENV;
   }