feat: support debug mode

Author: kettanaito

src/app-process.ts

@@ -1,4 +1,4 @@
-import { type ChildProcessWithoutNullStreams, spawn } from 'node:child_process'
+import { type ChildProcess, spawn } from 'node:child_process'
 import { DeferredPromise } from '@open-draft/deferred-promise'
 import { invariant } from '@epic-web/invariant'
 
@@ -11,7 +11,7 @@ export interface AppProcessOptions {
 export const kUrl = Symbol('kUrl')
 
 export class AppProcess {
-  private io?: ChildProcessWithoutNullStreams
+  private io?: ChildProcess
   private controller: AbortController
   private [kUrl]?: URL
 
@@ -30,7 +30,7 @@ export class AppProcess {
     return url
   }
 
-  public async launch(): Promise<ChildProcessWithoutNullStreams> {
+  public async launch(): Promise<ChildProcess> {
     const [command, ...args] = this.options.command.split(' ')
 
     invariant(

src/define-launcher.ts

@@ -1,4 +1,4 @@
-import type { ChildProcessWithoutNullStreams } from 'node:child_process'
+import type { ChildProcess } from 'node:child_process'
 import { AppProcess, kUrl } from './app-process.js'
 import { waitForPort } from './wait-for-port.js'
 
@@ -10,6 +10,11 @@ export interface DefineLauncherOptions<Context> {
    */
   extends?: Launcher
 
+  /**
+   * Run the launcher in debug mode.
+   */
+  debug?: boolean
+
   /**
    * Define a context object exposed to the other launcher methods.
    *
@@ -66,7 +71,7 @@ export interface DefineLauncherOptions<Context> {
   url: (options: {
     context: Context
     env: Record<string, string>
-    appProcess: ChildProcessWithoutNullStreams
+    appProcess: ChildProcess
   }) => string | URL | Promise<string | URL>
 }
 
@@ -108,6 +113,11 @@ export function defineLauncher<Context>(
       })
       const childProcess = await app.launch()
 
+      if (options?.debug) {
+        childProcess.stdout?.pipe(process.stdout)
+        childProcess.stderr?.pipe(process.stderr)
+      }
+
       // Wait for the provided application URL to be up.
       const url = await options.url({
         context,