Reapply "[turbopack] Add bundling support for worker_threads" (#88725) by lukesandberg · Pull Request #88967 · vercel/next.js

lukesandberg · 2026-01-23T18:09:37Z

What?

This PR reapplies #87746 which adds bundling support for Node.js worker_threads in Turbopack.

Why?

The original PR (#87746) was reverted in #88725 because it broke builds that use packages like pino with transports. These packages use dynamic patterns like join(__dirname, 'lib', 'worker.js') to resolve worker entry points, which can match non-evaluatable files like package.json or tsconfig.json.

How?

This PR reapplies the original changes with the following fixes:

Downgrade errors to warnings in tracing contexts: When loose_errors is enabled (tracing mode) or in_try is true, worker entry point validation errors are now emitted as warnings instead of errors. This follows the established Turbopack pattern used in handle_resolve_error and other resolve error handling.
Improved error messages: Error messages for non-chunkable and non-evaluatable worker entry point modules now include:
- The module identifier (so you can see which file caused the issue)
- The issue source location (pointing to the new Worker() call in source code)
Added regression test: A new pino-based test case exercises the thread-stream worker pattern that caused the original failure. This test runs in CodeGenerationAndTracing mode via test-start-turbo.

Changes from original PR

Added source field to CodeGenerationIssue to support showing issue source locations
Added get_issue_severity() helper that checks loose_errors and in_try to determine severity
Fixed typo: "SharedbWorker" → "SharedWorker" in to_string implementation
Added pino regression test in test/e2e/app-dir/node-worker-threads/

Testing

✅ pnpm test-dev-turbo test/e2e/app-dir/node-worker-threads/ - all tests pass
✅ pnpm test-start-turbo test/e2e/app-dir/node-worker-threads/ - all tests pass (exercises bundling mode)
✅ Verified test fails without the loose_errors fix
✅ Verified vercel-docs build succeeds with warnings instead of errors

lukesandberg · 2026-01-23T18:10:12Z

Reapply "[turbopack] Add bundling support for worker_threads" (#88725) #88967 👈 (View in Graphite)
canary

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nextjs-bot · 2026-01-23T18:20:43Z

Tests Passed

turbopack/crates/turbopack-ecmascript/src/references/worker.rs

nextjs-bot · 2026-01-23T18:31:24Z

Stats from current PR

✅ No significant changes detected

📊 All Metrics

📖 Metrics Glossary

Dev Server Metrics:

Listen = TCP port starts accepting connections
First Request = HTTP server returns successful response
Cold = Fresh build (no cache)
Warm = With cached build artifacts

Build Metrics:

Fresh = Clean build (no .next directory)
Cached = With existing .next directory

Change Thresholds:

Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
Size: Changes < 1KB AND < 1% are insignificant
All other changes are flagged to catch regressions

📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric	Canary	PR	Change	Trend
Cold (Listen)	456ms	506ms	✓	▁▁▁▁▁
Cold (Ready in log)	459ms	459ms	✓	▃▃▄▃▃
Cold (First Request)	1.893s	1.897s	✓	▂▂▃▂▂
Warm (Listen)	455ms	457ms	✓	▁▁▁▁▁
Warm (Ready in log)	459ms	458ms	✓	▃▃▄▄▃
Warm (First Request)	1.921s	1.905s	✓	▂▂▃▂▂

📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric	Canary	PR	Change	Trend
Fresh Build	14.474s	14.529s	✓	▁▁▂▁▁
Cached Build	14.601s	14.562s	✓	▁▁▂▄▁
node_modules Size	461 MB	461 MB	✓	█████

📦 Bundle Sizes

Bundle Sizes

📦 Webpack

Client

Main Bundles

	Canary	PR	Change
2086.HASH.js gzip	169 B	N/A	-
2161-HASH.js gzip	5.47 kB	N/A	-
2747-HASH.js gzip	4.53 kB	N/A	-
4322-HASH.js gzip	52.7 kB	N/A	-
ec793fe8-HASH.js gzip	62.3 kB	N/A	-
framework-HASH.js gzip	59.8 kB	59.8 kB	✓
main-app-HASH.js gzip	252 B	253 B	✓
main-HASH.js gzip	38.7 kB	39.1 kB	✓
webpack-HASH.js gzip	1.68 kB	1.68 kB	✓
1596.HASH.js gzip	N/A	169 B	-
2658-HASH.js gzip	N/A	52.4 kB	-
6349-HASH.js gzip	N/A	4.52 kB	-
7019-HASH.js gzip	N/A	5.49 kB	-
b17a3386-HASH.js gzip	N/A	62.3 kB	-
Total	226 kB	226 kB	⚠️ +53 B

Polyfills

	Canary	PR	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Total	39.4 kB	39.4 kB	✓

Pages

	Canary	PR	Change
_app-HASH.js gzip	194 B	193 B	✓
_error-HASH.js gzip	182 B	182 B	✓
css-HASH.js gzip	336 B	335 B	✓
dynamic-HASH.js gzip	1.8 kB	1.8 kB	✓
edge-ssr-HASH.js gzip	256 B	256 B	✓
head-HASH.js gzip	352 B	349 B	✓
hooks-HASH.js gzip	385 B	384 B	✓
image-HASH.js gzip	580 B	580 B	✓
index-HASH.js gzip	259 B	258 B	✓
link-HASH.js gzip	2.5 kB	2.51 kB	✓
routerDirect..HASH.js gzip	319 B	317 B	✓
script-HASH.js gzip	385 B	387 B	✓
withRouter-HASH.js gzip	316 B	315 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Total	7.97 kB	7.96 kB	✅ -8 B

Server

Edge SSR

	Canary	PR	Change
edge-ssr.js gzip	126 kB	126 kB	✓
page.js gzip	245 kB	240 kB	🟢 4.73 kB (-2%)
Total	371 kB	366 kB	✅ -4.61 kB

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	618 B	614 B	✓
middleware-r..fest.js gzip	155 B	156 B	✓
middleware.js gzip	33.1 kB	33.3 kB	✓
edge-runtime..pack.js gzip	842 B	842 B	✓
Total	34.7 kB	35 kB	⚠️ +240 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	736 B	738 B	✓
Total	736 B	738 B	⚠️ +2 B

Build Cache

	Canary	PR	Change
0.pack gzip	3.71 MB	3.72 MB	🔴 +9.49 kB (+0%)
index.pack gzip	102 kB	102 kB	✓
index.pack.old gzip	102 kB	101 kB	✓
Total	3.91 MB	3.92 MB	⚠️ +8.83 kB

🔄 Shared (bundler-independent)

Runtimes

	Canary	PR	Change
app-page-exp...dev.js gzip	307 kB	307 kB	✓
app-page-exp..prod.js gzip	163 kB	163 kB	✓
app-page-tur...dev.js gzip	307 kB	307 kB	✓
app-page-tur..prod.js gzip	163 kB	163 kB	✓
app-page-tur...dev.js gzip	303 kB	303 kB	✓
app-page-tur..prod.js gzip	161 kB	161 kB	✓
app-page.run...dev.js gzip	303 kB	303 kB	✓
app-page.run..prod.js gzip	161 kB	161 kB	✓
app-route-ex...dev.js gzip	70 kB	70 kB	✓
app-route-ex..prod.js gzip	48.6 kB	48.6 kB	✓
app-route-tu...dev.js gzip	70 kB	70 kB	✓
app-route-tu..prod.js gzip	48.6 kB	48.6 kB	✓
app-route-tu...dev.js gzip	69.6 kB	69.6 kB	✓
app-route-tu..prod.js gzip	48.4 kB	48.4 kB	✓
app-route.ru...dev.js gzip	69.6 kB	69.6 kB	✓
app-route.ru..prod.js gzip	48.4 kB	48.4 kB	✓
dist_client_...dev.js gzip	324 B	324 B	✓
dist_client_...dev.js gzip	326 B	326 B	✓
dist_client_...dev.js gzip	318 B	318 B	✓
dist_client_...dev.js gzip	317 B	317 B	✓
pages-api-tu...dev.js gzip	43 kB	43 kB	✓
pages-api-tu..prod.js gzip	32.7 kB	32.7 kB	✓
pages-api.ru...dev.js gzip	43 kB	43 kB	✓
pages-api.ru..prod.js gzip	32.7 kB	32.7 kB	✓
pages-turbo....dev.js gzip	52.3 kB	52.3 kB	✓
pages-turbo...prod.js gzip	39.2 kB	39.2 kB	✓
pages.runtim...dev.js gzip	52.2 kB	52.2 kB	✓
pages.runtim..prod.js gzip	39.2 kB	39.2 kB	✓
server.runti..prod.js gzip	62.4 kB	62.4 kB	✓
Total	2.74 MB	2.74 MB	✅ -3 B

codspeed-hq · 2026-01-23T18:33:26Z

Merging this PR will not alter performance

✅ 17 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing luke/revert-worker-threads-revert (0a129f3) with canary (bb88ea5)}

3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

turbopack/crates/turbopack-ecmascript/src/references/worker.rs

mmastrac

LGTM

turbopack/crates/turbopack-ecmascript/src/references/worker.rs

graphite-app · 2026-01-26T08:58:32Z

Merge activity

Jan 26, 8:58 AM UTC: This pull request can not be added to the Graphite merge queue. Please try rebasing and resubmitting to merge when ready.
Jan 26, 8:58 AM UTC: Graphite disabled "merge when ready" on this PR due to: a merge conflict with the target branch; resolve the conflict and try again..
Jan 26, 8:42 PM UTC: @lukesandberg merged this pull request with Graphite.

This reverts commit 1bbba2a.

- Add source field to CodeGenerationIssue to point at the worker instantiation location - Include the resolved module's ident in error messages for non-chunkable and non-evaluatable worker modules - Helps users understand both where the worker was created and which module caused the issue

…acing mode

…s unused

nextjs-bot added created-by: Turbopack team PRs by the Turbopack team. tests Turbopack Related to Turbopack with Next.js. labels Jan 23, 2026

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lukesandberg marked this pull request as ready for review January 23, 2026 21:36

lukesandberg force-pushed the luke/revert-worker-threads-revert branch from 66d3002 to 33e3c28 Compare January 24, 2026 03:15

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lukesandberg force-pushed the luke/revert-worker-threads-revert branch from fd92974 to db18661 Compare January 24, 2026 18:07

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lukesandberg and others added 9 commits January 26, 2026 10:51

Reapply "[turbopack] Add bundling support for worker_threads" (#88725)

c852f56

This reverts commit 1bbba2a.

simplify the merge by expanding WorkerType slightly

534a262

add a regression test for pino and downgrade module type errors in tr…

cb3013e

…acing mode

Remove reference_type from the resolve_options function it is alway…

da5d29f

…s unused

rename

9e2062a

update snapshots

7b2b3ae

restore type stripping for shared workers

92f8006

Update worker.rs

0a129f3

lukesandberg force-pushed the luke/revert-worker-threads-revert branch from db18661 to 0a129f3 Compare January 26, 2026 18:54

lukesandberg merged commit b690af0 into canary Jan 26, 2026
296 of 300 checks passed

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Reapply "[turbopack] Add bundling support for worker_threads" (#88725)#88967

Reapply "[turbopack] Add bundling support for worker_threads" (#88725)#88967
lukesandberg merged 9 commits intocanaryfrom
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