Report initialize_done event when server is ready

Summary: Adds a new reportable event, `initialize_done`, that is reported when the bundler has finished initialising everything that blocks handling bundle requests (namely loading the dependency graph and creating the transformer).

Reviewed By: GijsWeterings

Differential Revision: D30991582

fbshipit-source-id: 7843f261158c3dfbeaade6976aa6ea237c531d23

Author: motiz88

packages/metro/src/Bundler.js

@@ -24,12 +24,13 @@ export type BundlerOptions = $ReadOnly<{|
 
 class Bundler {
   _depGraphPromise: Promise<DependencyGraph>;
+  _readyPromise: Promise<void>;
   _transformer: Transformer;
 
   constructor(config: ConfigT, options?: BundlerOptions) {
     this._depGraphPromise = DependencyGraph.load(config, options);
 
-    this._depGraphPromise
+    this._readyPromise = this._depGraphPromise
       .then((dependencyGraph: DependencyGraph) => {
         this._transformer = new Transformer(
           config,
@@ -63,6 +64,11 @@ class Bundler {
 
     return this._transformer.transformFile(filePath, transformOptions);
   }
+
+  // Waits for the bundler to become ready.
+  async ready(): Promise<void> {
+    await this._readyPromise;
+  }
 }
 
 module.exports = Bundler;

packages/metro/src/IncrementalBundler.js

@@ -336,6 +336,11 @@ class IncrementalBundler {
 
     return absoluteEntryFiles;
   }
+
+  // Wait for the bundler to become ready.
+  async ready(): Promise<void> {
+    await this._bundler.ready();
+  }
 }
 
 module.exports = IncrementalBundler;

packages/metro/src/Server.js

@@ -1236,6 +1236,11 @@ class Server {
   _getEntryPointAbsolutePath(entryFile: string) {
     return path.resolve(this._getServerRootDir(), entryFile);
   }
+
+  // Wait for the server to finish initializing.
+  async ready(): Promise<void> {
+    await this._bundler.ready();
+  }
 }
 
 function* zip<X, Y>(xs: Iterable<X>, ys: Iterable<Y>): Iterable<[X, Y]> {

packages/metro/src/index.js

@@ -120,16 +120,38 @@ async function runMetro(
   options?: ServerOptions,
 ): Promise<MetroServer> {
   const mergedConfig = await getConfig(config);
+  const {
+    reporter,
+    server: {port},
+  } = mergedConfig;
 
-  mergedConfig.reporter.update({
+  reporter.update({
     hasReducedPerformance: options
       ? Boolean(options.hasReducedPerformance)
       : false,
-    port: mergedConfig.server.port,
+    port,
     type: 'initialize_started',
   });
 
-  return new MetroServer(mergedConfig, options);
+  const server = new MetroServer(mergedConfig, options);
+
+  server
+    .ready()
+    .then(() => {
+      reporter.update({
+        type: 'initialize_done',
+        port,
+      });
+    })
+    .catch(error => {
+      reporter.update({
+        type: 'initialize_failed',
+        port,
+        error,
+      });
+    });
+
+  return server;
 }
 
 exports.runMetro = runMetro;

packages/metro/src/lib/reporting.js

@@ -45,6 +45,10 @@ export type ReportableEvent =
       error: Error,
       ...
     }
+  | {
+      type: 'initialize_done',
+      port: number,
+    }
   | {
       buildID: string,
       type: 'bundle_build_done',