Turbopack: Extend filesystem watcher fuzzing to cover symlinks and junction points #88192

bgw · 2026-01-07T06:38:51Z

This is a crappy fuzzer I have to make sure that the filesystem watcher picks up changes to files. This didn't have coverage for links, so this tests that.

I tested this on Windows and Linux.

I don't care about the code quality here, so this was LLM-generated with very lightweight review.

bgw · 2026-01-07T06:39:09Z

Turbopack: Tweak retry loop for link creation to try to fix os error 80 on Windows #88669
Turbopack: Various cleanup for turbo-tasks-fs, mostly retry logic and string formatting #88668
Turbopack: Add a stress test / fuzzer that tries creating many symlinks in a tight loop #88667
Turbopack: Move fuzzer for fs watcher into a separate file/module #88666
Turbopack: Add file write invalidation tracking to filesystem watcher fuzzing #88665
Turbopack: Extend filesystem watcher fuzzing to cover symlinks and junction points #88192 👈 (View in Graphite)
canary

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nextjs-bot · 2026-01-07T07:08:40Z

Stats from current PR

🔴 2 regressions, 3 improvements

Metric	Canary	PR	Change
Turbo Build Time	4.258s	4.475s	🔴 +217ms (+5%)
Warm (Listen)	456ms	507ms	🔴 +51ms (+11%)
Turbo Build Time (cached)	4.383s	4.291s	🟢 92ms (-2%)
Cold (Listen)	507ms	456ms	🟢 51ms (-10%)
Warm (First Request)	401ms	356ms	🟢 45ms (-11%)

📊 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

Metric	Canary	PR	Change
Cold (Listen)	507ms	456ms	🟢 51ms (-10%)
Cold (First Request)	881ms	862ms	✓
Warm (Listen)	456ms	507ms	🔴 +51ms (+11%)
Warm (First Request)	401ms	356ms	🟢 45ms (-11%)

📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric	Canary	PR	Change
Cold (Listen)	456ms	455ms	✓
Cold (First Request)	1.807s	1.823s	✓
Warm (Listen)	456ms	455ms	✓
Warm (First Request)	1.810s	1.804s	✓

⚡ Production Builds

Metric	Canary	PR	Change
Fresh Build	4.258s	4.475s	🔴 +217ms (+5%)
Cached Build	4.383s	4.291s	🟢 92ms (-2%)

📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric	Canary	PR	Change	Trend
Fresh Build	13.767s	13.784s	✓
Cached Build	13.852s	13.891s	✓
node_modules Size	457 MB	457 MB	✓	▁████

📦 Bundle Sizes

Bundle Sizes

⚡ Turbopack

Client

Main Bundles: **430 kB** → **430 kB** ⚠️ +10 B

82 files with content-based hashes (individual files not comparable between builds)

Server

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	787 B	791 B	✓
Total	787 B	791 B	⚠️ +4 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	447 B	452 B	🔴 +5 B (+1%)
Total	447 B	452 B	⚠️ +5 B

📦 Webpack

Client

Main Bundles

	Canary	PR	Change
2086.HASH.js gzip	169 B	N/A	-
2161-HASH.js gzip	5.4 kB	N/A	-
2747-HASH.js gzip	4.48 kB	N/A	-
4322-HASH.js gzip	52.5 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	251 B	254 B	🔴 +3 B (+1%)
main-HASH.js gzip	38.4 kB	38.8 kB	✓
webpack-HASH.js gzip	1.68 kB	1.69 kB	✓
1596.HASH.js gzip	N/A	169 B	-
2658-HASH.js gzip	N/A	52.2 kB	-
6349-HASH.js gzip	N/A	4.46 kB	-
7019-HASH.js gzip	N/A	5.42 kB	-
b17a3386-HASH.js gzip	N/A	62.3 kB	-
Total	225 kB	225 kB	⚠️ +125 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	124 kB	124 kB	✓
page.js gzip	240 kB	240 kB	✓
Total	364 kB	365 kB	⚠️ +723 B

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	654 B	655 B	✓
middleware-r..fest.js gzip	155 B	156 B	✓
middleware.js gzip	32.8 kB	33 kB	✓
edge-runtime..pack.js gzip	846 B	846 B	✓
Total	34.4 kB	34.6 kB	⚠️ +173 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	738 B	738 B	✓
Total	738 B	738 B	✓

Build Cache

	Canary	PR	Change
0.pack gzip	3.62 MB	3.63 MB	🔴 +1.92 kB (+0%)
index.pack gzip	98.6 kB	99.2 kB	✓
index.pack.old gzip	99.1 kB	99.6 kB	✓
Total	3.82 MB	3.83 MB	⚠️ +3 kB

🔄 Shared (bundler-independent)

Runtimes

	Canary	PR	Change
app-page-exp...dev.js gzip	303 kB	303 kB	✓
app-page-exp..prod.js gzip	158 kB	158 kB	✓
app-page-tur...dev.js gzip	302 kB	302 kB	✓
app-page-tur..prod.js gzip	158 kB	158 kB	✓
app-page-tur...dev.js gzip	299 kB	299 kB	✓
app-page-tur..prod.js gzip	156 kB	156 kB	✓
app-page.run...dev.js gzip	299 kB	299 kB	✓
app-page.run..prod.js gzip	156 kB	156 kB	✓
app-route-ex...dev.js gzip	68.7 kB	68.7 kB	✓
app-route-ex..prod.js gzip	47.5 kB	47.5 kB	✓
app-route-tu...dev.js gzip	68.7 kB	68.7 kB	✓
app-route-tu..prod.js gzip	47.5 kB	47.5 kB	✓
app-route-tu...dev.js gzip	68.3 kB	68.3 kB	✓
app-route-tu..prod.js gzip	47.3 kB	47.3 kB	✓
app-route.ru...dev.js gzip	68.3 kB	68.3 kB	✓
app-route.ru..prod.js gzip	47.3 kB	47.3 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	41.1 kB	41.1 kB	✓
pages-api-tu..prod.js gzip	31.2 kB	31.2 kB	✓
pages-api.ru...dev.js gzip	41 kB	41 kB	✓
pages-api.ru..prod.js gzip	31.2 kB	31.2 kB	✓
pages-turbo....dev.js gzip	50.8 kB	50.8 kB	✓
pages-turbo...prod.js gzip	38.2 kB	38.2 kB	✓
pages.runtim...dev.js gzip	50.7 kB	50.7 kB	✓
pages.runtim..prod.js gzip	38.2 kB	38.2 kB	✓
server.runti..prod.js gzip	62.2 kB	62.2 kB	✓
Total	2.68 MB	2.68 MB	✅ -2 B

codspeed-hq · 2026-01-07T07:09:33Z

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing bgw/fuzz-symlink-and-junction-watching (60007dd) with canary (5a12867)}

Summary

✅ 17 untouched benchmarks
⏩ 3 skipped benchmarks¹

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. ↩

…nction points

cshein45

@cshein45

bgw · 2026-01-20T20:33:36Z

Merge activity

Jan 20, 8:33 PM UTC: A user started a stack merge that includes this pull request via Graphite.
Jan 20, 8:34 PM UTC: @bgw merged this pull request with Graphite.

nextjs-bot added created-by: Turbopack team PRs by the Turbopack team. Turbopack Related to Turbopack with Next.js. labels Jan 7, 2026

bgw force-pushed the bgw/fuzz-symlink-and-junction-watching branch 4 times, most recently from 0d4bbfd to 230f1de Compare January 7, 2026 06:43

Turbopack: Extend filesystem watcher fuzzing to cover symlinks and ju…

60007dd

…nction points

bgw force-pushed the bgw/fuzz-symlink-and-junction-watching branch from 230f1de to 60007dd Compare January 16, 2026 21:38

cshein45 reviewed Jan 16, 2026

View reviewed changes

bgw requested a review from a team January 16, 2026 22:20

bgw marked this pull request as ready for review January 16, 2026 22:41

lukesandberg approved these changes Jan 19, 2026

View reviewed changes

bgw merged commit d2ea7d3 into canary Jan 20, 2026
164 of 165 checks passed

bgw deleted the bgw/fuzz-symlink-and-junction-watching branch January 20, 2026 20:34

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Turbopack: Extend filesystem watcher fuzzing to cover symlinks and junction points #88192

Turbopack: Extend filesystem watcher fuzzing to cover symlinks and junction points #88192

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nextjs-bot commented Jan 7, 2026

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Turbopack: Extend filesystem watcher fuzzing to cover symlinks and junction points #88192

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nextjs-bot commented Jan 7, 2026

Stats from current PR

🔴 2 regressions, 3 improvements

⚡ Dev Server

📦 Dev Server (Webpack)

⚡ Production Builds

📦 Production Builds (Webpack)

Bundle Sizes

⚡ Turbopack

📦 Webpack

🔄 Shared (bundler-independent)

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CodSpeed Performance Report

Merging this PR will not alter performance

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