fix(cli): avoid destroying .nuxt while dev runs

packages/nuxi/src/commands/prepare.ts

@@ -6,6 +6,7 @@ import { resolve } from 'pathe'
 
 import { clearBuildDir } from '../utils/fs'
 import { loadKit } from '../utils/kit'
+import { readActiveLock } from '../utils/lockfile'
 import { logger } from '../utils/logger'
 import { relativeToProcess } from '../utils/paths'
 import { cwdArgs, dotEnvArgs, envNameArgs, extendsArgs, legacyRootDirArgs, logLevelArgs } from './_shared'
@@ -43,7 +44,20 @@ export default defineCommand({
         ...ctx.data?.overrides,
       },
     })
-    await clearBuildDir(nuxt.options.buildDir)
+
+    // Only wipe when nothing owns the buildDir. `clearBuildDir` removes the
+    // generated artifacts a live dev server's watcher reloads against, so it
+    // would resolve a freshly-deleted file (ENOENT); wiping under a build is
+    // equally destructive. `buildNuxt` refreshes every template in place anyway,
+    // so reuse is safe. Stop the owner if a clean wipe is genuinely needed.
+    const owner = readActiveLock(nuxt.options.buildDir)
+    if (owner) {
+      const label = owner.command === 'dev' ? 'dev server' : 'build'
+      logger.info(`A ${label} (PID ${owner.pid}) owns ${colors.cyan(relativeToProcess(nuxt.options.buildDir))}; refreshing templates in place without clearing.`)
+    }
+    else {
+      await clearBuildDir(nuxt.options.buildDir)
+    }
 
     await buildNuxt(nuxt)
     await writeTypes(nuxt)

packages/nuxi/src/commands/typecheck.ts

@@ -1,16 +1,18 @@
+import { existsSync } from 'node:fs'
 import process from 'node:process'
 
 import { cancel, confirm, isCancel, spinner } from '@clack/prompts'
 import { defineCommand } from 'citty'
 import { colors } from 'consola/utils'
 import { resolveModulePath } from 'exsolve'
 import { addDevDependency, detectPackageManager } from 'nypm'
-import { resolve } from 'pathe'
+import { join, resolve } from 'pathe'
 import { readTSConfig } from 'pkg-types'
 import { hasTTY } from 'std-env'
 import { x } from 'tinyexec'
 
 import { loadKit } from '../utils/kit'
+import { readActiveLocks } from '../utils/lockfile'
 import { logger } from '../utils/logger'
 import { cwdArgs, dotEnvArgs, extendsArgs, legacyRootDirArgs, logLevelArgs } from './_shared'
 
@@ -42,19 +44,55 @@ export default defineCommand({
     ...dotEnvArgs,
     ...extendsArgs,
     ...legacyRootDirArgs,
+    prepare: {
+      type: 'boolean',
+      description: 'Generate Nuxt types before checking. Defaults to auto: skipped when a dev server is already running for this project (default buildDir only). Use --no-prepare to force-reuse, --prepare to always prepare.',
+    },
   },
   async run(ctx) {
     process.env.NODE_ENV = process.env.NODE_ENV || 'production'
 
     const cwd = resolve(ctx.args.cwd || ctx.args.rootDir)
+    // Assume the default buildDir. Resolving a custom one means loading config,
+    // the cost we're trying to skip, so those fall through to preparing.
+    const buildDir = join(cwd, '.nuxt')
+
+    const decision = resolvePrepareDecision(buildDir, {
+      prepare: ctx.args.prepare as boolean | undefined,
+      extends: ctx.args.extends,
+    })
+
+    if (!decision.prepare && !existsSync(join(buildDir, 'tsconfig.json'))) {
+      logger.error(
+        `Cannot type check without prepared types: no \`${join(buildDir, 'tsconfig.json')}\` found. Run \`nuxt prepare\` or start the dev server first, or drop \`--no-prepare\`.`,
+      )
+      process.exitCode = 1
+      return
+    }
+
+    if (!decision.prepare && ctx.args.extends) {
+      logger.warn('`--extends` is ignored when prepare is skipped.')
+    }
+
+    if (!decision.prepare && hasTTY) {
+      logger.info(
+        decision.reusingDevPid
+          ? `Reusing types from the running dev server (PID ${decision.reusingDevPid}); skipping prepare.`
+          : 'Skipping prepare; type checking against the existing `.nuxt`.',
+      )
+    }
+
+    const preparePromise: Promise<void> = decision.prepare
+      ? writeTypes(cwd, ctx.args.dotenv, ctx.args.logLevel as 'silent' | 'info' | 'verbose', {
+          ...ctx.data?.overrides,
+          ...(ctx.args.extends && { extends: ctx.args.extends }),
+        })
+      : Promise.resolve()
 
     const [supportsProjects, vueTsc] = await Promise.all([
       readTSConfig(cwd).then(r => !!(r.references?.length)),
       ensureVueTsc(cwd, resolveDeps()),
-      writeTypes(cwd, ctx.args.dotenv, ctx.args.logLevel as 'silent' | 'info' | 'verbose', {
-        ...ctx.data?.overrides,
-        ...(ctx.args.extends && { extends: ctx.args.extends }),
-      }),
+      preparePromise,
     ])
 
     if (!vueTsc) {
@@ -82,6 +120,41 @@ export default defineCommand({
   },
 })
 
+export interface PrepareDecision {
+  prepare: boolean
+  /** PID of the live dev server we are reusing types from, when skipping. */
+  reusingDevPid?: number
+}
+
+/**
+ * Decide whether `typecheck` runs its own prepare. Skips it when a dev server
+ * owns this buildDir and has signalled `typesReady`, reusing its `.nuxt` rather
+ * than rebuilding (which would remove `.nuxt/dist` and restart dev). The
+ * `typesReady` gate avoids checking against mid-rebuild or stale types. Explicit
+ * `--prepare`/`--no-prepare` win; in auto mode `--extends` forces a prepare.
+ */
+export function resolvePrepareDecision(
+  buildDir: string,
+  opts: { prepare?: boolean, extends?: string },
+): PrepareDecision {
+  if (opts.prepare === true) {
+    return { prepare: true }
+  }
+  if (opts.prepare === false) {
+    return { prepare: false }
+  }
+  if (opts.extends) {
+    return { prepare: true }
+  }
+
+  // Reuse types from any live dev server that has signalled readiness.
+  const devLock = readActiveLocks(buildDir).find(l => l.command === 'dev' && l.typesReady === true)
+  if (devLock && existsSync(join(buildDir, 'tsconfig.json'))) {
+    return { prepare: false, reusingDevPid: devLock.pid }
+  }
+  return { prepare: true }
+}
+
 async function ensureVueTsc(cwd: string, deps: Record<DepName, string | undefined>): Promise<string | undefined> {
   const missing = (Object.keys(REQUIRED_DEPS) as DepName[]).filter(name => !deps[name])
   if (missing.length === 0) {

packages/nuxi/src/dev/utils.ts

@@ -198,8 +198,8 @@ export class NuxtDevServer extends EventEmitter<DevServerEventMap> {
 
     await this.#loadNuxtInstance()
 
-    // Acquire lock before binding a listener so parallel agent invocations
-    // fail fast without starting a second server (agent-only).
+    // Acquire the lock before binding a listener so a conflicting build fails
+    // fast, and so typecheck can detect this server.
     this.#acquireDevLock(this.#currentNuxt!.options.buildDir)
 
     if (this.options.showBanner) {
@@ -345,6 +345,14 @@ export class NuxtDevServer extends EventEmitter<DevServerEventMap> {
       throw new Error('Nuxt must be loaded before configuration')
     }
 
+    // Mark types stale while (re)building so a concurrent typecheck won't reuse
+    // mid-rebuild output; set ready again after the build below.
+    updateLock(this.#currentNuxt.options.buildDir, {
+      command: 'dev',
+      cwd: this.options.cwd,
+      typesReady: false,
+    })
+
     // Connect Vite HMR
     if (!process.env.NUXI_DISABLE_VITE_HMR) {
       this.#currentNuxt.hooks.hook('vite:extend', ({ config }) => {
@@ -487,6 +495,8 @@ export class NuxtDevServer extends EventEmitter<DevServerEventMap> {
       port: addr.port,
       hostname: addr.address,
       url: serverUrl,
+      // Types are built for the current instance; typecheck may reuse them.
+      typesReady: true,
     })
 
     this.emit('ready', serverUrl)
@@ -506,14 +516,23 @@ export class NuxtDevServer extends EventEmitter<DevServerEventMap> {
   }
 
   #acquireDevLock(buildDir: string): void {
+    // Advertise this dev server so `nuxt typecheck` can detect it and skip its
+    // prepare. Peer dev servers may run concurrently, so this never refuses
+    // another dev, though it still refuses a live build.
     const lock = acquireLock(buildDir, {
       command: 'dev',
       cwd: this.options.cwd,
-    })
+    }, { enforce: false })
     if (lock.existing) {
       console.error(formatLockError(lock.existing))
       throw new Error(`Another Nuxt ${lock.existing.command} is already running (PID ${lock.existing.pid}).`)
     }
+    // We coexist with peer dev servers rather than refuse them, but they share
+    // this `.nuxt` — concurrent writes/watches can trigger conflicting reloads.
+    const peerDev = lock.peers?.find(l => l.command === 'dev')
+    if (peerDev) {
+      console.warn(`Another Nuxt dev server is already running (PID ${peerDev.pid}); reusing the same \`.nuxt\` build dir. Run on a separate buildDir to avoid conflicting reloads.`)
+    }
     // Swap atomically: install the new release before freeing the old one so
     // we're never unlocked in between.
     const previousRelease = this.#lockCleanup

packages/nuxi/src/utils/fs.ts

@@ -20,7 +20,9 @@ export async function clearDir(path: string, exclude?: string[]) {
 }
 
 export function clearBuildDir(path: string) {
-  return clearDir(path, ['cache', 'analyze', 'nuxt.json', 'nuxt.lock'])
+  // Keep `locks/` (and the legacy `nuxt.lock`) so a wipe never deletes a
+  // presence marker a peer dev/build process holds (see utils/lockfile).
+  return clearDir(path, ['cache', 'analyze', 'nuxt.json', 'nuxt.lock', 'locks'])
 }
 
 export async function rmRecursive(paths: string[]) {