Add back support for the assetPlugin option

Summary:
**Summary**
Metro used to have support for "asset plugins", which allowed developers to specify arbitrary JS modules that could export a function for adding more fields to asset data objects. Some of this functionality was removed in the delta bundler work -- this PR adds it back.

**Test plan**
Made existing unit tests pass and added unit tests to test asset plugin behavior. Also tested E2E in a React Native project by adding `assetPlugin=/path/to/pluginModule` to a JS bundle URL and ensuring that the plugin ran.
Closes https://github.com/facebook/metro/pull/118

Differential Revision: D6711094

Pulled By: rafeca

fbshipit-source-id: f42c54cfd11bac5103194f85083084eef25fa3cd

packages/metro/src/Assets/__tests__/Assets-test.js

@@ -19,9 +19,12 @@ const {getAssetData, getAsset} = require('../');
 const crypto = require('crypto');
 const fs = require('fs');
 
+const mockImageWidth = 300;
+const mockImageHeight = 200;
+
 require('image-size').mockReturnValue({
-  width: 300,
-  height: 200,
+  width: mockImageWidth,
+  height: mockImageHeight,
 });
 
 describe('getAsset', () => {
@@ -160,7 +163,7 @@ describe('getAssetData', () => {
       },
     });
 
-    return getAssetData('/root/imgs/b.png', 'imgs/b.png').then(data => {
+    return getAssetData('/root/imgs/b.png', 'imgs/b.png', []).then(data => {
       expect(data).toEqual(
         expect.objectContaining({
           __packager_asset: true,
@@ -192,7 +195,7 @@ describe('getAssetData', () => {
       },
     });
 
-    const data = await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg');
+    const data = await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg', []);
 
     expect(data).toEqual(
       expect.objectContaining({
@@ -212,6 +215,67 @@ describe('getAssetData', () => {
     );
   });
 
+  it('loads and runs asset plugins', async () => {
+    jest.mock(
+      'mockPlugin1',
+      () => {
+        return asset => {
+          asset.extraReverseHash = asset.hash
+            .split('')
+            .reverse()
+            .join('');
+          return asset;
+        };
+      },
+      {virtual: true},
+    );
+
+    jest.mock(
+      'asyncMockPlugin2',
+      () => {
+        return async asset => {
+          expect(asset.extraReverseHash).toBeDefined();
+          asset.extraPixelCount = asset.width * asset.height;
+          return asset;
+        };
+      },
+      {virtual: true},
+    );
+
+    fs.__setMockFilesystem({
+      root: {
+        imgs: {
+          'b@1x.png': 'b1 image',
+          'b@2x.png': 'b2 image',
+          'b@3x.png': 'b3 image',
+        },
+      },
+    });
+
+    const data = await getAssetData('/root/imgs/b.png', 'imgs/b.png', [
+      'mockPlugin1',
+      'asyncMockPlugin2',
+    ]);
+
+    expect(data).toEqual(
+      expect.objectContaining({
+        __packager_asset: true,
+        type: 'png',
+        name: 'b',
+        scales: [1, 2, 3],
+        fileSystemLocation: '/root/imgs',
+        httpServerLocation: '/assets/imgs',
+        files: [
+          '/root/imgs/b@1x.png',
+          '/root/imgs/b@2x.png',
+          '/root/imgs/b@3x.png',
+        ],
+        extraPixelCount: mockImageWidth * mockImageHeight,
+      }),
+    );
+    expect(typeof data.extraReverseHash).toBe('string');
+  });
+
   describe('hash:', () => {
     let mockFS;
 
@@ -237,17 +301,21 @@ describe('getAssetData', () => {
         hash.update(mockFS.root.imgs[name]);
       }
 
-      expect(await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg')).toEqual(
+      expect(await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg', [])).toEqual(
         expect.objectContaining({hash: hash.digest('hex')}),
       );
     });
 
     it('changes the hash when the passed-in file watcher emits an `all` event', async () => {
-      const initialData = await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg');
+      const initialData = await getAssetData(
+        '/root/imgs/b.jpg',
+        'imgs/b.jpg',
+        [],
+      );
 
       mockFS.root.imgs['b@4x.jpg'] = 'updated data';
 
-      const data = await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg');
+      const data = await getAssetData('/root/imgs/b.jpg', 'imgs/b.jpg', []);
       expect(data.hash).not.toEqual(initialData.hash);
     });
   });

packages/metro/src/Assets/index.js

@@ -50,6 +50,10 @@ export type AssetData = AssetDataWithoutFiles & {
   +files: Array<string>,
 };
 
+export type AssetDataPlugin = (
+  assetData: AssetData,
+) => AssetData | Promise<AssetData>;
+
 const hashFiles = denodeify(function hashFilesCb(files, hash, callback) {
   if (!files.length) {
     callback(null);
@@ -234,6 +238,7 @@ async function getAbsoluteAssetInfo(
 async function getAssetData(
   assetPath: string,
   localPath: string,
+  assetDataPlugins: $ReadOnlyArray<string>,
   platform: ?string = null,
 ): Promise<AssetData> {
   let assetUrlPath = path.join('/assets', path.dirname(localPath));
@@ -244,22 +249,38 @@ async function getAssetData(
   }
 
   const isImage = isAssetTypeAnImage(path.extname(assetPath).slice(1));
-  const assetData = await getAbsoluteAssetInfo(assetPath, platform);
-  const dimensions = isImage ? imageSize(assetData.files[0]) : null;
-  const scale = assetData.scales[0];
+  const assetInfo = await getAbsoluteAssetInfo(assetPath, platform);
+  const dimensions = isImage ? imageSize(assetInfo.files[0]) : null;
+  const scale = assetInfo.scales[0];
 
-  return {
+  const assetData = {
     __packager_asset: true,
     fileSystemLocation: path.dirname(assetPath),
     httpServerLocation: assetUrlPath,
     width: dimensions ? dimensions.width / scale : undefined,
     height: dimensions ? dimensions.height / scale : undefined,
-    scales: assetData.scales,
-    files: assetData.files,
-    hash: assetData.hash,
-    name: assetData.name,
-    type: assetData.type,
+    scales: assetInfo.scales,
+    files: assetInfo.files,
+    hash: assetInfo.hash,
+    name: assetInfo.name,
+    type: assetInfo.type,
   };
+  return await applyAssetDataPlugins(assetDataPlugins, assetData);
+}
+
+async function applyAssetDataPlugins(
+  assetDataPlugins: $ReadOnlyArray<string>,
+  assetData: AssetData,
+): Promise<AssetData> {
+  if (!assetDataPlugins.length) {
+    return assetData;
+  }
+
+  const [currentAssetPlugin, ...remainingAssetPlugins] = assetDataPlugins;
+  // $FlowFixMe: impossible to type a dynamic require.
+  const assetPluginFunction: AssetDataPlugin = require(currentAssetPlugin);
+  const resultAssetData = await assetPluginFunction(assetData);
+  return await applyAssetDataPlugins(remainingAssetPlugins, resultAssetData);
 }
 
 /**

packages/metro/src/DeltaBundler/DeltaCalculator.js

@@ -159,6 +159,7 @@ class DeltaCalculator extends EventEmitter {
     } = this._bundler.getGlobalTransformOptions();
 
     const transformOptionsForBlacklist = {
+      assetDataPlugins: this._options.assetPlugins,
       enableBabelRCLookup,
       dev: this._options.dev,
       hot: this._options.hot,

packages/metro/src/DeltaBundler/Serializers.js

@@ -238,7 +238,12 @@ async function getAssets(
           module.path,
         );
 
-        return getAssetData(module.path, localPath, options.platform);
+        return getAssetData(
+          module.path,
+          localPath,
+          options.assetPlugins,
+          options.platform,
+        );
       }
       return null;
     }),

packages/metro/src/DeltaBundler/__tests__/DeltaCalculator-test.js

@@ -297,6 +297,7 @@ describe('DeltaCalculator', () => {
   describe('getTransformerOptions()', () => {
     it('should calculate the transform options correctly', async () => {
       expect(await deltaCalculator.getTransformerOptions()).toEqual({
+        assetDataPlugins: [],
         dev: true,
         enableBabelRCLookup: false,
         hot: true,
@@ -315,6 +316,7 @@ describe('DeltaCalculator', () => {
       );
 
       expect(await deltaCalculator.getTransformerOptions()).toEqual({
+        assetDataPlugins: [],
         dev: true,
         enableBabelRCLookup: false,
         hot: true,
@@ -333,6 +335,7 @@ describe('DeltaCalculator', () => {
       );
 
       expect(await deltaCalculator.getTransformerOptions()).toEqual({
+        assetDataPlugins: [],
         dev: true,
         enableBabelRCLookup: false,
         hot: true,

packages/metro/src/DeltaBundler/__tests__/Serializers-test.js

@@ -78,11 +78,13 @@ describe('Serializers', () => {
       },
     };
 
-    getAssetData.mockImplementation((path, localPath, platform) => ({
-      path,
-      platform,
-      assetData: true,
-    }));
+    getAssetData.mockImplementation(
+      (path, localPath, assetDataPlugins, platform) => ({
+        path,
+        platform,
+        assetData: true,
+      }),
+    );
 
     toLocalPath.mockImplementation((roots, path) => path.replace(roots[0], ''));
 

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

@@ -61,6 +61,7 @@ export type Transformer<ExtraOptions: {} = {}> = {
 };
 
 export type TransformOptionsStrict = {|
+  +assetDataPlugins: $ReadOnlyArray<string>,
   +enableBabelRCLookup: boolean,
   +dev: boolean,
   +hot: boolean,
@@ -71,6 +72,7 @@ export type TransformOptionsStrict = {|
 |};
 
 export type TransformOptions = {
+  +assetDataPlugins: $ReadOnlyArray<string>,
   +enableBabelRCLookup?: boolean,
   +dev?: boolean,
   +hot?: boolean,
@@ -200,7 +202,11 @@ function transformCode(
   };
 
   const transformResult = isAsset(filename, assetExts)
-    ? assetTransformer.transform(transformerArgs, assetRegistryPath)
+    ? assetTransformer.transform(
+        transformerArgs,
+        assetRegistryPath,
+        options.assetDataPlugins,
+      )
     : transformer.transform(transformerArgs);
 
   const postTransformArgs = [

packages/metro/src/ModuleGraph/worker/__tests__/transform-module-test.js

@@ -88,6 +88,7 @@ describe('transforming JS modules:', () => {
   });
 
   const defaults = {
+    assetDataPlugins: [],
     dev: false,
     hot: false,
     inlineRequires: false,

packages/metro/src/ModuleGraph/worker/transform-module.js

@@ -49,6 +49,7 @@ export type TransformOptions<ExtraOptions> = {|
 
 const NODE_MODULES = path.sep + 'node_modules' + path.sep;
 const defaultTransformOptions = {
+  assetDataPlugins: [],
   dev: false,
   hot: false,
   inlineRequires: false,

packages/metro/src/assetTransformer.js

@@ -27,6 +27,7 @@ type Params = {
 async function transform(
   {filename, localPath, options, src}: Params,
   assetRegistryPath: string,
+  assetDataPlugins: $ReadOnlyArray<string>,
 ): Promise<{ast: Ast}> {
   options = options || {
     platform: '',
@@ -35,7 +36,12 @@ async function transform(
     minify: false,
   };
 
-  const data = await getAssetData(filename, localPath, options.platform);
+  const data = await getAssetData(
+    filename,
+    localPath,
+    assetDataPlugins,
+    options.platform,
+  );
 
   return {
     ast: generateAssetCodeFileAst(assetRegistryPath, data),

packages/metro/src/lib/__tests__/__snapshots__/getTransformCacheKeyFn-test.js.snap

@@ -1,3 +1,3 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`getTransformCacheKeyFn Should return always the same key for the same params 1`] = `"4f055d9baf74ca63c449a03d12d3ea5e06dce486012af2c6d0afa156e0a3350ab9187479"`;
+exports[`getTransformCacheKeyFn Should return always the same key for the same params 1`] = `"78c7c4254ad9c8290da4f45eec858cee4466daae32be6252a9bc5b8df65171914db10f84"`;

packages/metro/src/transformer.js

@@ -122,6 +122,7 @@ type Params = {
 
 function transform({filename, options, src, plugins}: Params) {
   options = options || {
+    assetDataPlugins: [],
     platform: '',
     projectRoot: '',
     inlineRequires: false,