Support named exports from client references (#20312)

* Rename "name"->"filepath" field on Webpack module references

This field name will get confused with the imported name or the module id.

* Switch back to transformSource instead of getSource

getSource would be more efficient in the cases where we don't need to read
the original file but we'll need to most of the time.

Even then, we can't return a JS file if we're trying to support non-JS
loader because it'll end up being transformed.

Similarly, we'll need to parse the file and we can't parse it before it's
transformed. So we need to chain with other loaders that know how.

* Add acorn dependency

This should be the version used by Webpack since we have a dependency on
Webpack anyway.

* Parse exported names of ESM modules

We need to statically resolve the names that a client component will
export so that we can export a module reference for each of the names.

For export * from, this gets tricky because we need to also load the
source of the next file to parse that. We don't know exactly how the
client is built so we guess it's somewhat default.

* Handle imported names one level deep in CommonJS using a Proxy

We use a proxy to see what property the server access and that will tell
us which property we'll want to import on the client.

* Add export name to module reference and Webpack map

To support named exports each name needs to be encoded as a separate
reference. It's possible with module splitting that different exports end
up in different chunks.

It's also possible that the export is renamed as part of minification.
So the map also includes a map from the original to the bundled name.

* Special case plain CJS requires and conditional imports using __esModule

This models if the server tries to import .default or a plain require.
We should replicate the same thing on the client when we load that
module reference.

* Dedupe acorn-related deps

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

Author: sebmarkbage

fixtures/flight/loader/index.js

@@ -1,4 +1,8 @@
-import {resolve, getSource} from 'react-transport-dom-webpack/node-loader';
+import {
+  resolve,
+  getSource,
+  transformSource as reactTransformSource,
+} from 'react-transport-dom-webpack/node-loader';
 
 export {resolve, getSource};
 
@@ -13,7 +17,7 @@ const babelOptions = {
   ],
 };
 
-export async function transformSource(source, context, defaultTransformSource) {
+async function babelTransformSource(source, context, defaultTransformSource) {
   const {format} = context;
   if (format === 'module') {
     const opt = Object.assign({filename: context.url}, babelOptions);
@@ -22,3 +26,9 @@ export async function transformSource(source, context, defaultTransformSource) {
   }
   return defaultTransformSource(source, context, defaultTransformSource);
 }
+
+export async function transformSource(source, context, defaultTransformSource) {
+  return reactTransformSource(source, context, (s, c) => {
+    return babelTransformSource(s, c, defaultTransformSource);
+  });
+}

fixtures/flight/server/handler.server.js

@@ -17,14 +17,35 @@ module.exports = async function(req, res) {
   pipeToNodeWritable(<App />, res, {
     // TODO: Read from a map on the disk.
     [resolve('../src/Counter.client.js')]: {
-      id: './src/Counter.client.js',
-      chunks: ['1'],
-      name: 'default',
+      Counter: {
+        id: './src/Counter.client.js',
+        chunks: ['2'],
+        name: 'Counter',
+      },
+    },
+    [resolve('../src/Counter2.client.js')]: {
+      Counter: {
+        id: './src/Counter2.client.js',
+        chunks: ['1'],
+        name: 'Counter',
+      },
     },
     [resolve('../src/ShowMore.client.js')]: {
-      id: './src/ShowMore.client.js',
-      chunks: ['2'],
-      name: 'default',
+      default: {
+        id: './src/ShowMore.client.js',
+        chunks: ['3'],
+        name: 'default',
+      },
+      '': {
+        id: './src/ShowMore.client.js',
+        chunks: ['3'],
+        name: '',
+      },
+      '*': {
+        id: './src/ShowMore.client.js',
+        chunks: ['3'],
+        name: '*',
+      },
     },
   });
 };

fixtures/flight/src/App.server.js

@@ -2,7 +2,8 @@ import * as React from 'react';
 
 import Container from './Container.js';
 
-import Counter from './Counter.client.js';
+import {Counter} from './Counter.client.js';
+import {Counter as Counter2} from './Counter2.client.js';
 
 import ShowMore from './ShowMore.client.js';
 
@@ -11,6 +12,7 @@ export default function App() {
     <Container>
       <h1>Hello, world</h1>
       <Counter />
+      <Counter2 />
       <ShowMore>
         <p>Lorem ipsum</p>
       </ShowMore>

fixtures/flight/src/Counter.client.js

@@ -2,7 +2,7 @@ import * as React from 'react';
 
 import Container from './Container.js';
 
-export default function Counter() {
+export function Counter() {
   const [count, setCount] = React.useState(0);
   return (
     <Container>

fixtures/flight/src/Counter2.client.js

@@ -0,0 +1 @@
+export * from './Counter.client.js';

packages/react-transport-dom-webpack/package.json

@@ -50,6 +50,7 @@
     "webpack": "^4.43.0"
   },
   "dependencies": {
+    "acorn": "^6.2.1",
     "loose-envify": "^1.1.0",
     "object-assign": "^4.1.1"
   },

packages/react-transport-dom-webpack/src/ReactFlightClientWebpackBundlerConfig.js

@@ -59,5 +59,16 @@ export function requireModule<T>(moduleData: ModuleReference<T>): T {
       throw entry;
     }
   }
-  return __webpack_require__(moduleData.id)[moduleData.name];
+  const moduleExports = __webpack_require__(moduleData.id);
+  if (moduleData.name === '*') {
+    // This is a placeholder value that represents that the caller imported this
+    // as a CommonJS module as is.
+    return moduleExports;
+  }
+  if (moduleData.name === '') {
+    // This is a placeholder value that represents that the caller accessed the
+    // default property of this if it was an ESM interop module.
+    return moduleExports.__esModule ? moduleExports.default : moduleExports;
+  }
+  return moduleExports[moduleData.name];
 }

packages/react-transport-dom-webpack/src/ReactFlightServerWebpackBundlerConfig.js

@@ -8,14 +8,17 @@
  */