Turbopack production build eliminates entire function body of a `/* @__PURE__ */`-wrapped self-invoking function, including its side effects

Link to the code that reproduces this issue

https://github.com/dexterouschen/turbopack-pure-annotation-dce-repro

To Reproduce

npm install, then npm run build && npm run start, open localhost:3000, watch "Tick count" stay at 0 forever. Compare with npm run dev — same page, counter climbs continuously.

Current vs. Expected behavior

Expected: the "Tick count" counter climbs continuously (~hundreds/sec) via a requestAnimationFrame loop started in a useEffect.

Actual: in a production build only, the counter never increments past 0. Inspecting .next/static/chunks/*.js shows the entire startTicking(setCount) call — including the callback invocation and the requestAnimationFrame scheduling — compiled away to useEffect(() => () => window.cancelAnimationFrame(0), []).

The triggering pattern is a self-invoking named function expression passed through a /* @__PURE__ */-annotated name-preserving helper (the same shape esbuild/tsup emit with keepNames, and shipped as-is by npm packages like @radix-ui/react-scroll-area). The minifier appears to extend the @__PURE__ annotation's scope from the helper call it directly precedes to the separate, subsequent invocation of that call's return value — even though invoking the returned function has clear, necessary side effects (mutating closure state, invoking a caller-supplied callback, scheduling further work).

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.6.0: Sat Jul 11 15:25:34 PDT 2026; root:xnu-12377.161.13~4/RELEASE_ARM64_T6020
  Available memory (MB): 16384
  Available CPU cores: 10
Binaries:
  Node: 26.7.0
  npm: 11.19.0
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.3.1 // Latest available version is detected (16.3.1).
  eslint-config-next: N/A
  react: 19.2.8
  react-dom: 19.2.8
  typescript: 7.0.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Turbopack

Which stage(s) are affected? (Select all that apply)

next build (local)

Additional context

This was discovered via a real-world regression: @radix-ui/react-scroll-area@1.2.18's addUnlinkedScrollListener (in dist/index.mjs) uses this exact pattern to drive live scrollbar-thumb position tracking during scroll. In a Next.js 16 + Turbopack production build, the same elimination causes the scrollbar thumb to freeze while the user is actively scrolling — it only updates once per fresh "listener registration" (e.g. on mouse re-enter, or after a scroll pause/resume), which is exactly the "increments once, then freezes" behavior this minimal repro demonstrates. We worked around it locally with a pnpm patch that restructures the function to avoid the IIFE + adjacent-annotation shape (happy to share the patch diff if useful for a fix).

Start with the linked turbopack-pure-annotation-dce-repro repository: run npm install, compare npm run build && npm run start with npm run dev, and inspect the generated .next/static/chunks/*.js output. Trace how the annotated helper and subsequent self-invoking function are handled during the Turbopack production build. Done means the production counter keeps incrementing and the necessary callback and requestAnimationFrame side effects remain present.