[edbzn]

Fixes #641.

Builds on #607 (transformForBrowser, merged).

Problem

@oxc-angular/vite leaves async/await native. zone.js can't track a native await, so fakeAsync with tick()/flushMicrotasks() can't drive code that awaits, and change detection after an await doesn't run as a zone task. The Angular CLI downlevels async to generators when zone.js is in the polyfills (esbuild supported: { 'async-await': false }, getFeatureSupport in @angular/build).

Fix

A new sub-plugin, @oxc-angular/vite-downlevel-async, runs #607's transformForBrowser with downlevelAsync: true on application scripts that contain async (not node_modules).

• Why feat(napi): transformForBrowser - TypeScript with Angular's settings, async lowered for zone.js #607 and not a config hook: Vite 8 transforms with Oxc. Oxc's target downlevels by ES version, with no per-feature switch like esbuild's supported. The Angular CLI's own Vite dev server hits the same limit and falls back to es2016 for dependencies. That would also downlevel spread, optional chaining and class fields. esbuild.supported needs esbuild, and esbuild's inline var __async helper breaks under vi.mock hoisting (see vite: async/await is not lowered for zone.js, so fakeAsync/tick cannot control awaits #641).
• Order: the plugin is enforce: 'post', with a normal-order transform hook. So it runs:
  • after TypeScript is stripped. It passes that code as JavaScript, so only async is downleveled and class fields are left alone;
  • after Vitest hoists vi.mock(). If the downleveling ran first, an async mock factory would become an eager _asyncToGenerator(...) call, and hoisting would move it above its helper's import: Cannot access '__vi_import_1__' before initialization;
  • before vite:import-analysis, which resolves the helper imports for the dev server. A hook-level order: 'post' would run after it, and the browser would get a bare @oxc-project/runtime/... import.
• Module mode: the code is named .mjs (.jsx for JSX files), because Vite serves it as a module. As .js, a file without import/export would get its helpers through require().
• Helpers are imported from @oxc-project/runtime. Vite 8 resolves them without the package being installed: its builtin oxc-runtime plugin covers dev and Vitest, and Rolldown inlines them in builds. No new dependency.
• When: the existing zoneless option was unused. It now controls the downleveling. When it is unset, an app is zoneless unless node_modules/zone.js exists above the Vite root. That replaces the CLI's signal, zone.js in the polyfills, which a Vite app doesn't declare.
• Not covered:
  • Server (SSR) transforms stay native, as feat(napi): transformForBrowser - TypeScript with Angular's settings, async lowered for zone.js #607 intends. The CLI does downlevel its server main bundle for zone apps.
  • Vitest's node environment transforms as SSR, so it keeps async native too. The README says to run zone.js specs in jsdom, happy-dom or the browser.
  • Dependencies (node_modules and pre-bundled deps), which the CLI also downlevels.

Checks

• New test/downlevel-async.test.ts (9 tests):
  • async is downleveled;
  • a class field stays a field;
  • a file without import/export gets imported helpers, not require();
  • an error is reported by its message;
  • a dev-server request (transformRequest) gets the helper import resolved by import analysis;
  • async stays native when zoneless, and in SSR transforms;
  • the default follows whether zone.js is installed;
  • a nested Vitest run in a client environment, with an async vi.mock factory. It fails if the hook runs before the hoisting.
• Checked by hand, not committed because zone.js isn't a dependency of this package: the fakeAsync + flushMicrotasks() repro from vite: async/await is not lowered for zone.js, so fakeAsync/tick cannot control awaits #641 under Vitest with zone.js 0.16.3. It passes with the downleveling. With zoneless: true it fails with expected "vi.fn()" to be called at least once.
• Checked by hand: a Vite dev server in headless Chromium, with an async module and a file without import/export. Both run in zone and zoneless modes.
• Checked by hand: a vite build with async code. The helpers are inlined from Rolldown's runtime and no async is left. A zoneless build keeps it native.
• On the branch (merged with main):
  • vitest run --dir ./test: 21 files, 397 tests pass.
  • tsc -p tsconfig.json --noEmit is clean.
  • oxfmt --check and oxlint --type-aware --type-check are clean on the changed files.

🤖 Generated with Claude Code

[Brooooooklyn]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	🔄 Running since 2026-10-27T15:18:31.702381Z	13020eb	Manual request

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[Brooooooklyn]

@codex review