add debug statements to debugger shell launching path (#54929)

Summary:
Pull Request resolved: #54929

There's a bug in Node.JS: nodejs/node#51018 where spawning a process on Windows with detached mode and unref will not actually inherit stdio. You need to manually pipe these to get to see stdout and stderr. It works well on MacOS though.

Changelog: [Internal]

Reviewed By: huntie

Differential Revision: D88955169

fbshipit-source-id: cba661b13d8636d4d52122fe024f876300d4af1f

Author: vzaidman

packages/debugger-shell/src/node/index.flow.js

@@ -14,6 +14,7 @@ import {
 } from './private/LaunchUtils';
 
 const {spawn} = require('cross-spawn');
+const debug = require('debug')('Metro:Debugger:DebuggerShell');
 const path = require('path');
 
 // The 'prebuilt' flavor will use the prebuilt shell binary (and the JavaScript embedded in it).
@@ -55,36 +56,59 @@ async function unstable_spawnDebuggerShellWithArgs(
       ...env
     } = process.env;
     const child = spawn(binaryPath, [...baseArgs, ...args], {
-      stdio: 'inherit',
+      stdio: ['ignore', 'pipe', 'pipe'],
       windowsHide: true,
       detached: mode === 'detached',
       env,
     });
     if (mode === 'detached') {
       child.on('spawn', () => {
+        debug('Debugger spawned in detached mode');
         resolve();
       });
-      child.on('close', (code: number) => {
+      child.on('close', (code: number, signal) => {
+        debug('Debugger closed with code %s and signal %s', code, signal);
         if (code !== 0) {
+          console.error(
+            'Debugger closed with code %s and signal %s',
+            code,
+            signal,
+          );
           reject(
             new Error(
               `Failed to open debugger shell: exited with code ${code}`,
             ),
           );
         }
       });
+      child.on('error', error => {
+        debug('Debugger shell encountered error: %s', error);
+        reject(error);
+      });
+      child.stdout.on('data', data =>
+        console.debug('[DebuggerShell stdout] ' + String(data)),
+      );
+      child.stderr.on('data', data =>
+        console.debug('[DebuggerShell stderr] ' + String(data)),
+      );
       child.unref();
     } else if (mode === 'syncThenExit') {
       child.on('close', function (code, signal) {
+        debug('Debugger closed with code %s and signal %s', code, signal);
         if (code === null) {
-          console.error('Debugger shell exited with signal', signal);
+          console.error(
+            'Debugger closed with code %s and signal %s',
+            code,
+            signal,
+          );
           process.exit(1);
         }
         process.exit(code);
       });
 
       const handleTerminationSignal = function (signal: string) {
         process.on(signal, function signalHandler() {
+          debug('The Signal %s received. killing debugger', signal);
           if (!child.killed) {
             child.kill(signal);
           }