Print a message when the watcher of babel-cli is ready.

packages/babel-cli/src/babel/dir.ts

@@ -225,6 +225,8 @@ export default async function ({
       watcher.watch(filenameOrDir);
     });
 
+    watcher.startWatcher();
+
     watcher.onFilesChange(async filenames => {
       processing++;
       if (startTime === null) startTime = process.hrtime();

packages/babel-cli/src/babel/file.ts

@@ -201,6 +201,8 @@ export default async function ({
     if (cliOptions.watch) {
       filenames.forEach(watcher.watch);
 
+      watcher.startWatcher();
+
       watcher.onFilesChange((changes, event, cause) => {
         const actionableChange = changes.some(
           filename =>

packages/babel-cli/src/babel/watcher.ts

@@ -6,6 +6,8 @@ const depToFiles = new Map<string, Set<string>>();
 
 let isWatchMode = false;
 let watcher;
+const watchQueue = new Set<string>();
+let hasStarted = false;
 
 export function enable({ enableGlobbing }: { enableGlobbing: boolean }) {
   isWatchMode = true;
@@ -25,14 +27,31 @@ export function enable({ enableGlobbing }: { enableGlobbing: boolean }) {
   watcher.on("unlink", unwatchFile);
 }
 
+export function startWatcher() {
+  hasStarted = true;
+
+  for (const dep of watchQueue) {
+    watcher.add(dep);
+  }
+  watchQueue.clear();
+
+  watcher.on("ready", () => {
+    console.log("The watcher is ready.");
+  });
+}
+
 export function watch(filename: string): void {
   if (!isWatchMode) {
     throw new Error(
       "Internal Babel error: .watch called when not in watch mode.",
     );
   }
 
-  watcher.add(path.resolve(filename));
+  if (!hasStarted) {
+    watchQueue.add(path.resolve(filename));
+  } else {
+    watcher.add(path.resolve(filename));
+  }
 }
 
 /**
@@ -86,7 +105,11 @@ export function updateExternalDependencies(
     if (!depToFiles.has(dep)) {
       depToFiles.set(dep, new Set());
 
-      watcher.add(dep);
+      if (!hasStarted) {
+        watchQueue.add(dep);
+      } else {
+        watcher.add(dep);
+      }
     }
     depToFiles.get(dep).add(absFilename);
   }
@@ -100,7 +123,11 @@ function removeFileDependency(filename: string, dep: string) {
   if (depToFiles.get(dep).size === 0) {
     depToFiles.delete(dep);
 
-    watcher.unwatch(dep);
+    if (!hasStarted) {
+      watchQueue.delete(dep);
+    } else {
+      watcher.unwatch(dep);
+    }
   }
 }
 

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch --verbose with external dependencies/executor.js

@@ -11,10 +11,11 @@ const run = (async function* () {
   assert.match(files[1], /src[\\/]main.js -> lib[\\/]main.js/);
   assert.match(yield, /Successfully compiled 2 files with Babel \(\d+ms\)\./);
 
+  assert.equal(yield, "The watcher is ready.");
+
   logFile("lib/index.js");
   logFile("lib/main.js");
-  // wait 2s for watcher setup
-  await new Promise(resolve => setTimeout(resolve, 2000));
+
   fs.writeFileSync("./file.txt", "Updated!");
 
   files = [yield, yield].sort();

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch --verbose with external dependencies/stdout.txt

@@ -1,6 +1,7 @@
 BATCHED(0) src/index.js -> lib/index.js
 BATCHED(0) src/main.js -> lib/main.js
 Successfully compiled 2 files with Babel (123ms).
+The watcher is ready.
 EXECUTOR lib/index.js "let str = /"Hi :)/";"
 EXECUTOR lib/main.js "console.log(/"Hi :)/");"
 BATCHED(1) src/index.js -> lib/index.js

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch multiple dir/executor.js

@@ -8,8 +8,8 @@ if (!assert.match) assert.match = (val, re) => assert(re.test(val));
 const run = (async function* () {
   assert.match(yield, /Successfully compiled 4 files with Babel \(\d+ms\)\./);
 
-  // wait 2s for watcher setup
-  await new Promise(resolve => setTimeout(resolve, 2000));
+  assert.equal(yield, "The watcher is ready.");
+
   // update ./module1/src/index.js
   fs.writeFileSync(
     "./module1/src/index.js",

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch multiple dir/stdout.txt

@@ -1,2 +1,3 @@
 Successfully compiled 4 files with Babel (123ms).
+The watcher is ready.
 Successfully compiled 1 file with Babel (123ms).

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch with external dependencies/executor.js

@@ -8,10 +8,11 @@ if (!assert.match) assert.match = (val, re) => assert(re.test(val));
 const run = (async function* () {
   assert.match(yield, /Successfully compiled 2 files with Babel \(\d+ms\)\./);
 
+  assert.equal(yield, "The watcher is ready.");
+
   logFile("lib/index.js");
   logFile("lib/main.js");
-  // wait 2s for watcher setup
-  await new Promise(resolve => setTimeout(resolve, 2000));
+
   fs.writeFileSync("./file.txt", "Updated!");
 
   assert.match(yield, /Successfully compiled 2 files with Babel \(\d+ms\)\./);

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch with external dependencies/stdout.txt

@@ -1,4 +1,5 @@
 Successfully compiled 2 files with Babel (123ms).
+The watcher is ready.
 EXECUTOR lib/index.js "let str = /"Hi :)/";"
 EXECUTOR lib/main.js "console.log(/"Hi :)/");"
 Successfully compiled 2 files with Babel (123ms).