[lukesandberg]

Summary

#98836 added an on-demand __turbopack_ensure_chunk__ hook to the Turbopack Node dev runtime by overriding __turbopack_context__.l. The override returned ensured.then(() => loadChunkAsync(...)), so every call that hit a not-yet-cached chunk produced a new promise, and the first caller's promise never matched the one later callers got from chunkCache. That broke referential identity for __next_chunk_load__ (which wraps .l), which React relies on. It also created extra promises for React's dev async tracking to process.

This change makes loadChunkAsync itself aware of __turbopack_ensure_chunk__:

• The hook is called synchronously on a cache miss. If it returns undefined (nothing to compile), the chunk is required synchronously and the shared pre-resolved promise is cached, exactly as without the hook.
• If it returns a promise (the chunk is being compiled on demand), a single ensure → require/install promise is cached in chunkCache immediately. Concurrent and later callers all get the same promise until clearChunkCache().
• If ensuring the chunk fails (a synchronous throw or an async rejection), the failure is not cached, so the next load retries. require failures stay cached as ChunkLoadError, as before.
• The separate .l override and chunksBeingEnsured map in dev-base.ts are removed. The Node runtime snapshots are regenerated.

On the Next.js side, the dev hook is now a plain function. It returns synchronously for chunks that aren't lazy-compilation chunks, or that have no matching entries, and returns a promise only when it actually activates a lazy chunk.

Verification

• pnpm test-dev-turbo test/development/app-dir/lazy-dynamic-imports/lazy-dynamic-imports.test.ts (12/12 pass)

• A scratch Node script against the generated dev and build runtimes, with a mocked ensure hook. It checks:

  • async ensure: same promise for concurrent and post-settle calls, ensure called once, modules installed only after ensure, and eviction plus retry after an ensure failure
  • sync ensure: modules installed synchronously with the shared resolved promise, and no caching after a synchronous throw
  • cached ChunkLoadError, non-JS chunks, and clearChunkCache reset

  The identity and sync-path checks fail on the previous runtime and pass with this change.

[github-actions]

Tests Passed

Commit: f8e30eb