perf(dev): warm the fork pool on first file change instead of on ready

Author: danielroe

packages/nuxt-cli/src/commands/dev.ts

@@ -153,7 +153,7 @@ const command = defineCommand({
 }
 
 // Start the initial dev server in-process with listener
-const{ listener, close, reload, onRestart, onReady }=awaitinitialize({ cwd,args: ctx.args},{
+const{ listener, close, reload, onRestart, onReady, onFileChange}=awaitinitialize({ cwd,args: ctx.args},{
 data: ctx.data,
  listenOverrides,
 showBanner: true,
@@ -176,14 +176,18 @@ const command = defineCommand({
  inspect,
 })
 
-// When ready, start warming up the fork pool
 onReady((_address)=>{
-pool.startWarming()
 if(startTime){
 debug(`Dev server ready for connections in ${Date.now()-startTime}ms`)
 }
 })
 
+// Warming costs a whole extra Node process, so wait until the user shows
+// signs of editing the project rather than paying for it on every `nuxt dev`.
+onFileChange(()=>{
+pool.startWarming()
+})
+
 // On hard restart, use a fork from the pool
 letcleanupCurrentFork: (()=>Promise<void>)|undefined
 

packages/nuxt-cli/src/dev/index.ts

@@ -63,6 +63,8 @@ interface InitializeReturn {
 /** Reload Nuxt in place, keeping the current listener. */
 reload: (reason?: string)=>Promise<void>
 onReady: (callback: (address: string)=>void)=>void
+/** Called the first time a watched file changes, before Nuxt reloads. */
+onFileChange: (callback: ()=>void)=>void
 onRestart: (callback: (devServer: NuxtDevServer)=>void)=>void
 }
 
@@ -171,6 +173,9 @@ export async function initialize(devContext: NuxtDevContext, ctx: InitializeOpti
 devServer.once('ready',payload=>callback(payload))
 }
 },
+onFileChange: (callback: ()=>void)=>{
+devServer.once('change',callback)
+},
 onRestart: (callback: (devServer: NuxtDevServer)=>void)=>{
 letrestarted=false
 functionrestart(){

packages/nuxt-cli/src/dev/utils.ts

@@ -153,6 +153,7 @@ interface DevServerEventMap {
 'loading': [loadingMessage: string]
 'ready': [address: string]
 'restart': []
+'change': []
 }
 
 exportclassNuxtDevServerextendsEventEmitter<DevServerEventMap>{
@@ -390,6 +391,10 @@ export class NuxtDevServer extends EventEmitter<DevServerEventMap> {
 thrownewError('Nuxt must be loaded before configuration')
 }
 
+this.#currentNuxt.hooks.hook('builder:watch',()=>{
+this.emit('change')
+})
+
 // Connect Vite HMR
 if(!process.env.NUXI_DISABLE_VITE_HMR){
 this.#currentNuxt.hooks.hook('vite:extend',({ config })=>{
@@ -613,7 +618,10 @@ export class NuxtDevServer extends EventEmitter<DevServerEventMap> {
 this.#cwd,
 this.options.dotenv.fileName,
 ()=>this.emit('restart'),
-file=>this.loadDebounced(true,`${file} updated`),
+(file)=>{
+this.emit('change')
+this.loadDebounced(true,`${file} updated`)
+},
 getLocalLayerDirs(this.#currentNuxt?.options._layers??[],this.#cwd),
 )
 }