Fix HMR plugin on the OpenSource React Native transformer

Summary: This fixes facebook/react-native#21490

Reviewed By: jeanlauliac

Differential Revision: D10216508

fbshipit-source-id: d857918e281e0d1c02644bb7fcbe201026d2224a

Author: rafeca

packages/metro/src/integration_tests/__tests__/__snapshots__/server-test.js.snap

@@ -1,6 +1,35 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`should create a server 1`] = `
+exports[`Metro development server serves bundles via HTTP should serve deveopment bundles 1`] = `
+Object {
+  "Bar": Object {
+    "foo": "foo",
+    "type": "bar",
+  },
+  "Foo": Object {
+    "asset": Object {
+      "__packager_asset": true,
+      "hash": "77d45c1f7fa73c0f6c444a830dc42f67",
+      "height": 8,
+      "httpServerLocation": "/assets",
+      "name": "test",
+      "scales": Array [
+        1,
+      ],
+      "type": "png",
+      "width": 8,
+    },
+    "type": "foo",
+  },
+  "TypeScript": Object {
+    "B": [Function],
+    "test": true,
+    "type": "TypeScript",
+  },
+}
+`;
+
+exports[`Metro development server serves bundles via HTTP should serve production bundles 1`] = `
 Object {
   "Bar": Object {
     "foo": "foo",

packages/metro/src/integration_tests/__tests__/server-test.js

@@ -19,33 +19,55 @@ jest.unmock('cosmiconfig');
 
 jasmine.DEFAULT_TIMEOUT_INTERVAL = 60 * 1000;
 
-it('should create a server', async () => {
-  const config = await Metro.loadConfig({
-    config: require.resolve('../metro.config.js'),
-  });
-
-  const httpServer = await Metro.runServer(config, {
-    reporter: {update() {}},
-  });
+describe('Metro development server serves bundles via HTTP', () => {
+  let config;
+  let httpServer;
 
-  try {
+  async function downloadAndExec(path: string): mixed {
     const response = await fetch(
-      `http://localhost:${
-        config.server.port
-      }/TestBundle.bundle?platform=ios&dev=false&minify=true`,
+      'http://localhost:' + config.server.port + path,
     );
 
     const body = await response.text();
 
     if (!response.ok) {
       console.error(body);
+
       throw new Error(
         'Metro server responded with status code: ' + response.status,
       );
     }
 
-    expect(execBundle(body)).toMatchSnapshot();
-  } finally {
-    httpServer.close();
+    return execBundle(body);
   }
+
+  beforeEach(async () => {
+    config = await Metro.loadConfig({
+      config: require.resolve('../metro.config.js'),
+    });
+
+    httpServer = await Metro.runServer(config, {
+      reporter: {update() {}},
+    });
+  });
+
+  afterEach(() => {
+    httpServer.close();
+  });
+
+  it('should serve deveopment bundles', async () => {
+    expect(
+      await downloadAndExec(
+        '/TestBundle.bundle?platform=ios&dev=true&minify=false',
+      ),
+    ).toMatchSnapshot();
+  });
+
+  it('should serve production bundles', async () => {
+    expect(
+      await downloadAndExec(
+        '/TestBundle.bundle?platform=ios&dev=false&minify=true',
+      ),
+    ).toMatchSnapshot();
+  });
 });

packages/metro/src/reactNativeTransformer.js

@@ -129,7 +129,10 @@ function buildBabelConfig(filename, options, plugins?: BabelPlugins = []) {
   config.plugins = extraPlugins.concat(config.plugins, plugins);
 
   if (options.dev && options.hot) {
-    const hmrConfig = makeHMRConfig(options, filename);
+    const hmrConfig = makeHMRConfig(
+      options,
+      path.resolve(options.projectRoot, filename),
+    );
     config = Object.assign({}, config, hmrConfig);
   }