server.close() hangs forever when a dependency is discovered mid-optimize (optimizer never settles its processing promise) #22934

Describe the bug

What I'm doing: running a Vitest browser-mode suite (vitest run, which drives a Vite dev server) on a cold optimizer cache, where dependencies are discovered progressively while the dep optimizer is still running.

What I expect: once the tests finish, vitest run exits.

What actually happens: the tests pass, but vitest run never exits — the process hangs indefinitely and has to be killed manually. The hang is the Vite dev server's close() never resolving during teardown.

Root cause — createDepsOptimizer() (packages/vite/src/node/optimizer/optimizer.ts) leaves a depOptimizationProcessing promise permanently unresolved when the server is closed while an optimize run is in flight:

• The optimizer tracks pending work with a current depOptimizationProcessing promise plus a queue of enqueued ones. A dep discovered via registerMissingImport gets optimizedDepInfo.processing set to the current promise; startNextDiscoveredBatch() later moves it into the queue.
• On shutdown these are settled inconsistently: runOptimizer()'s pre-optimize closed guard resolves the current and the enqueued promises; its post-optimize closed guard resolves only the enqueued ones; and close() resolves neither.
• So a dep discovered into the current batch while a run is in flight keeps a forever-pending .processing. Its vite:optimized-deps load() awaits info.processing forever → the request never leaves environment._pendingRequests → DevEnvironment.close()'s drain loop (while (this._pendingRequests.size > 0) await ...) never finishes → close() never resolves.

Reproduced on vite 8.0.8 and 8.1.4.

I intend to submit a PR. The proposed fix is to have close() settle the pending promises, mirroring runOptimizer's pre-optimize closed guard:

 async function close() {
   closed = true
+  depOptimizationProcessing.resolve()
+  resolveEnqueuedProcessingPromises()
   await Promise.allSettled([
     discover?.cancel(),
     depsOptimizer.scanProcessing,
     optimizationResult?.cancel(),
   ])
 }

Reproduction

https://github.com/bent0b0x/vite-optimizer-orphan-hang

Steps to reproduce

npm install
npm test

The test passes, then the process hangs and never exits (kill with Ctrl-C). Applying the included fix.patch to vite makes npm test exit cleanly.

The two small plugins in vitest.config.ts only make the race deterministic — slow-optimize keeps an optimize run in flight at teardown, and slow-chain opens a >100ms gap between dependency discoveries so one lands on the in-flight run's current batch. They are timing controls, not the cause: with fix.patch applied, the identical config exits cleanly. The same race arises naturally on a cold optimizer cache when dependencies are discovered progressively during a slow pre-bundle (e.g. a Vitest browser run with coverage.include + default server.preTransformRequests).

System Info

System:    macOS 26.5.1, arm64 (Apple M1 Max)
Binaries:  Node 22.14.0, npm 10.9.2, pnpm 10.33.0
Browsers:  Chrome 150.0.7871.102
npmPackages:
  vite: ^8 => 8.1.4
  vitest: ^4 => 4.1.10
  @vitest/browser-playwright: ^4 => 4.1.10
  playwright: ^1.59 => 1.61.1

Used Package Manager

npm

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.