Turbopack: remove sourcemapping comments #88217

mischnic · 2026-01-07T12:25:59Z

Otherwise there are stray sourceMappingURL comments in the middle of the chunks.

mischnic · 2026-01-07T12:26:27Z

Turbopack: remove sourcemapping comments #88217 👈 (View in Graphite)
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turbopack/crates/turbopack-ecmascript/src/swc_comments.rs

nextjs-bot · 2026-01-07T12:35:13Z

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nextjs-bot · 2026-01-07T12:58:20Z

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

Metric	Canary	PR	Change	Trend
Cold (Listen)	456ms	455ms	✓	█▁▁▁▁
Cold (Ready in log)	436ms	437ms	✓	▂▇▇▆█
Cold (First Request)	819ms	814ms	✓	▂▇███
Warm (Listen)	455ms	456ms	✓	▁▅▁▁▅
Warm (Ready in log)	435ms	437ms	✓	█▁▁▄▁
Warm (First Request)	333ms	336ms	✓	██▂▂▁

📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric	Canary	PR	Change	Trend
Cold (Listen)	455ms	455ms	✓	████▁
Cold (Ready in log)	435ms	434ms	✓	▇██▇▁
Cold (First Request)	1.730s	1.732s	✓	▄█▅▅▁
Warm (Listen)	456ms	455ms	✓	▅▅▅▁▁
Warm (Ready in log)	434ms	432ms	✓	▅▇▇▇▁
Warm (First Request)	1.746s	1.740s	✓	▅█▆▆▁

⚡ Production Builds

Metric	Canary	PR	Change	Trend
Fresh Build	4.016s	4.038s	✓	█▁▁▂▃
Cached Build	4.063s	4.053s	✓	█▁▂▂▂

📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric	Canary	PR	Change	Trend
Fresh Build	13.825s	13.805s	✓	▂█▁▂▁
Cached Build	13.886s	13.886s	✓	▁█▁▂▁
node_modules Size	457 MB	457 MB	✓	█████

📦 Bundle Sizes

Bundle Sizes

⚡ Turbopack

Client

Main Bundles: **430 kB** → **430 kB** ✅ -29 B

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

Server

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	788 B	788 B	✓
Total	788 B	788 B	✓

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	451 B	450 B	✓
Total	451 B	450 B	✅ -1 B

📦 Webpack

Client

Main Bundles

	Canary	PR	Change
2086.HASH.js gzip	169 B	N/A	-
2161-HASH.js gzip	5.41 kB	N/A	-
2747-HASH.js gzip	4.48 kB	N/A	-
4322-HASH.js gzip	52.8 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	38.6 kB	39 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	52.7 kB	-
6349-HASH.js gzip	N/A	4.46 kB	-
7019-HASH.js gzip	N/A	5.43 kB	-
b17a3386-HASH.js gzip	N/A	62.3 kB	-
Total	225 kB	226 kB	⚠️ +244 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	125 kB	125 kB	✓
page.js gzip	239 kB	239 kB	✓
Total	364 kB	364 kB	⚠️ +274 B

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	653 B	652 B	✓
middleware-r..fest.js gzip	155 B	156 B	✓
middleware.js gzip	32.9 kB	33.1 kB	✓
edge-runtime..pack.js gzip	842 B	842 B	✓
Total	34.6 kB	34.8 kB	⚠️ +208 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	3.62 MB	🔴 +5.96 kB (+0%)
index.pack gzip	98.2 kB	99.2 kB	🔴 +983 B (+1%)
index.pack.old gzip	98.8 kB	99.4 kB	✓
Total	3.82 MB	3.82 MB	⚠️ +7.53 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	303 kB	303 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	300 kB	300 kB	✓
app-page.run..prod.js gzip	156 kB	156 kB	✓
app-route-ex...dev.js gzip	68.2 kB	68.2 kB	✓
app-route-ex..prod.js gzip	46.9 kB	46.9 kB	✓
app-route-tu...dev.js gzip	68.2 kB	68.2 kB	✓
app-route-tu..prod.js gzip	46.9 kB	46.9 kB	✓
app-route-tu...dev.js gzip	67.8 kB	67.8 kB	✓
app-route-tu..prod.js gzip	46.7 kB	46.7 kB	✓
app-route.ru...dev.js gzip	67.8 kB	67.8 kB	✓
app-route.ru..prod.js gzip	46.7 kB	46.7 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	41.1 kB	41.1 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	50.8 kB	50.8 kB	✓
pages.runtim..prod.js gzip	38.2 kB	38.2 kB	✓
server.runti..prod.js gzip	62 kB	62 kB	✓
Total	2.68 MB	2.68 MB	⚠️ +3 B

codspeed-hq · 2026-01-07T13:00:23Z

Merging this PR will not alter performance

✅ 17 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing mischnic/extract-source-mapping-url (5e82116) with canary (f814b8b)}

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. ↩

sokra · 2026-01-07T13:05:38Z

turbopack/crates/turbopack-ecmascript/src/source_map.rs

+    file_content.rfind("\n//").and_then(|start| {
+        let line = &file_content[start..];
+        SOURCE_MAP_FILE_REFERENCE
+            .captures(line)
+            .map(|m| m.get(1).unwrap().as_str())
+    })


That's not completely correct. It's doesn't have to be the fall comment:

//# sourceMappingURL=... //# sourceURL=... // could be any extra comment too...

Here is the spec how to extract the comment: https://tc39.es/ecma426/#sec-linking-inline
But also see the ISSUE 1 box here.

Yes. But to be fair, this codepath is only used by RawEcmascriptModule right now (i.e. the devtools bundle).

…by position in file, per ECMAScript spec

nextjs-bot · 2026-01-12T12:41:13Z

Tests Passed

mischnic · 2026-01-13T14:05:44Z

Merge activity

Jan 13, 2:05 PM UTC: @mischnic 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

vercel bot reviewed Jan 7, 2026

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turbopack/crates/turbopack-ecmascript/src/swc_comments.rs Show resolved Hide resolved

mischnic force-pushed the mischnic/extract-source-mapping-url branch from 1e95fe7 to 2620abc Compare January 7, 2026 12:32

mischnic force-pushed the mischnic/extract-source-mapping-url branch from 90cdcdf to 89781ab Compare January 7, 2026 12:36

sokra reviewed Jan 7, 2026

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mischnic force-pushed the mischnic/extract-source-mapping-url branch from 89781ab to 281fde8 Compare January 7, 2026 14:52

mischnic marked this pull request as ready for review January 8, 2026 08:54

mischnic requested a review from sokra January 12, 2026 09:25

sokra approved these changes Jan 12, 2026

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naveenkarmegam approved these changes Jan 12, 2026

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mischnic and others added 3 commits January 12, 2026 13:22

Turbopack: remove sourcemapping comments

9fb1a3a

Fix: Fixed sourceMappingURL comment selection to choose the last one …

7334b4a

…by position in file, per ECMAScript spec

add comment

5e82116

mischnic force-pushed the mischnic/extract-source-mapping-url branch from 281fde8 to 5e82116 Compare January 12, 2026 12:22

mischnic merged commit 6339e63 into canary Jan 13, 2026
290 of 293 checks passed

mischnic deleted the mischnic/extract-source-mapping-url branch January 13, 2026 14:05

Turbopack: remove sourcemapping comments #88217

Turbopack: remove sourcemapping comments #88217

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Merging this PR will not alter performance

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