cli: add helper to wait for child to exit + use to fix watch-deps

packages/cli/src/commands/watch-deps/child.ts

@@ -34,4 +34,5 @@ export function startChild(args: string[]) {
   child.stderr!.on('data', data => {
     log.err(data.toString('utf8'));
   });
+  return child;
 }

packages/cli/src/commands/watch-deps/index.ts

@@ -22,6 +22,7 @@ import { getPackageDeps } from './packages';
 import { startWatcher, startPackageWatcher } from './watcher';
 import { startCompiler } from './compiler';
 import { startChild } from './child';
+import { waitForExit } from '../../helpers/run';
 
 const PACKAGE_BLACKLIST = [
   // We never want to watch for changes in the cli, but all packages will depend on it.
@@ -67,6 +68,6 @@ export default async (_command: any, args: string[]) => {
   });
 
   if (args?.length) {
-    startChild(args);
+    await waitForExit(startChild(args));
   }
 };

packages/cli/src/helpers/run.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { SpawnSyncOptions, spawn } from 'child_process';
+import { SpawnSyncOptions, spawn, ChildProcess } from 'child_process';
 import { ExitCodeError } from './errors';
 
 // Runs a child command, returning a promise that is only resolved if the child exits with code 0.
@@ -23,20 +23,33 @@ export async function run(
   args: string[] = [],
   options: SpawnSyncOptions = {},
 ) {
-  return new Promise((resolve, reject) => {
-    const env: NodeJS.ProcessEnv = {
-      ...process.env,
-      FORCE_COLOR: 'true',
-      ...(options.env ?? {}),
-    };
+  const env: NodeJS.ProcessEnv = {
+    ...process.env,
+    FORCE_COLOR: 'true',
+    ...(options.env ?? {}),
+  };
 
-    const child = spawn(name, args, {
-      stdio: 'inherit',
-      shell: true,
-      ...options,
-      env,
-    });
+  const child = spawn(name, args, {
+    stdio: 'inherit',
+    shell: true,
+    ...options,
+    env,
+  });
 
+  await waitForExit(child);
+}
+
+export async function waitForExit(
+  child: ChildProcess & { exitCode?: number },
+): Promise<void> {
+  if (typeof child.exitCode === 'number') {
+    if (child.exitCode) {
+      throw new ExitCodeError(child.exitCode, name);
+    }
+    return;
+  }
+
+  await new Promise((resolve, reject) => {
     child.once('error', error => reject(error));
     child.once('exit', code => {
       if (code) {