Stop sourcemapping function names

[eps1lon]

Sourcemaps will only give you the name mapping for a specific source position.
However, stack traces will point to the actual callsite not the function declaration.
So we always ask for the name mapping of the variable that we called not the name of the calling function.

We can fix this in v8 by using callsite.getEnclosingColumnNumber() - 1 but this is more involved since we need to stash the callsites in Error.prepareStacktrace for later inspection.

Since all the sourcemapping currently targets dev, we just stop sourcemapping functions names assuming most code is not mangled. That holds at least true for all product code.

Turbopack just used to work since it didn't include name mapping in sourcemaps in dev because it's unnecessary for unmangled code. Webpack always included name mapping even if it was 1:1 so that's why all of the discrepancies were observed in Webpack.

[eps1lon]

• Stop sourcemapping function names #74085 👈 (View in Graphite)
• Name default Jest project according to used env variables #74084
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[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
buildDuration	21.7s	19.7s	N/A
buildDurationCached	18.6s	16.4s	N/A
nodeModulesSize	416 MB	416 MB	⚠️ +5.47 kB
nextStartRea..uration (ms)	536ms	517ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
1187-HASH.js gzip	52.4 kB	52.4 kB	N/A
8276.HASH.js gzip	169 B	168 B	N/A
8377-HASH.js gzip	5.36 kB	5.36 kB	N/A
bccd1874-HASH.js gzip	53 kB	53 kB	N/A
framework-HASH.js gzip	57.5 kB	57.5 kB	N/A
main-app-HASH.js gzip	232 B	235 B	N/A
main-HASH.js gzip	34.1 kB	34.1 kB	N/A
webpack-HASH.js gzip	1.71 kB	1.71 kB	N/A
Overall change	0 B	0 B	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Overall change	39.4 kB	39.4 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
_app-HASH.js gzip	193 B	193 B	✓
_error-HASH.js gzip	193 B	193 B	✓
amp-HASH.js gzip	512 B	510 B	N/A
css-HASH.js gzip	343 B	342 B	N/A
dynamic-HASH.js gzip	1.84 kB	1.84 kB	✓
edge-ssr-HASH.js gzip	265 B	265 B	✓
head-HASH.js gzip	363 B	362 B	N/A
hooks-HASH.js gzip	393 B	392 B	N/A
image-HASH.js gzip	4.49 kB	4.49 kB	N/A
index-HASH.js gzip	268 B	268 B	✓
link-HASH.js gzip	2.35 kB	2.34 kB	N/A
routerDirect..HASH.js gzip	328 B	328 B	✓
script-HASH.js gzip	397 B	397 B	✓
withRouter-HASH.js gzip	323 B	326 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.59 kB	3.59 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
_buildManifest.js gzip	749 B	746 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
index.html gzip	524 B	524 B	✓
link.html gzip	539 B	537 B	N/A
withRouter.html gzip	520 B	521 B	N/A
Overall change	524 B	524 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
edge-ssr.js gzip	129 kB	129 kB	N/A
page.js gzip	205 kB	205 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
middleware-b..fest.js gzip	671 B	667 B	N/A
middleware-r..fest.js gzip	155 B	156 B	N/A
middleware.js gzip	31.3 kB	31.3 kB	N/A
edge-runtime..pack.js gzip	844 B	844 B	✓
Overall change	844 B	844 B	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
274-experime...dev.js gzip	322 B	322 B	✓
274.runtime.dev.js gzip	314 B	314 B	✓
app-page-exp...dev.js gzip	356 kB	356 kB	✓
app-page-exp..prod.js gzip	129 kB	129 kB	✓
app-page-tur..prod.js gzip	142 kB	142 kB	✓
app-page-tur..prod.js gzip	137 kB	137 kB	✓
app-page.run...dev.js gzip	347 kB	347 kB	✓
app-page.run..prod.js gzip	125 kB	125 kB	✓
app-route-ex...dev.js gzip	37.5 kB	37.5 kB	✓
app-route-ex..prod.js gzip	25.5 kB	25.5 kB	✓
app-route-tu..prod.js gzip	25.5 kB	25.5 kB	✓
app-route-tu..prod.js gzip	25.3 kB	25.3 kB	✓
app-route.ru...dev.js gzip	39.1 kB	39.1 kB	✓
app-route.ru..prod.js gzip	25.3 kB	25.3 kB	✓
pages-api-tu..prod.js gzip	9.69 kB	9.69 kB	✓
pages-api.ru...dev.js gzip	11.6 kB	11.6 kB	✓
pages-api.ru..prod.js gzip	9.68 kB	9.68 kB	✓
pages-turbo...prod.js gzip	21.7 kB	21.7 kB	✓
pages.runtim...dev.js gzip	27.5 kB	27.5 kB	✓
pages.runtim..prod.js gzip	21.7 kB	21.7 kB	✓
server.runti..prod.js gzip	916 kB	916 kB	N/A
Overall change	1.51 MB	1.51 MB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	vercel/next.js sebbie/12-18-stop_sourcemapping_function_names	Change
0.pack gzip	2.08 MB	2.08 MB	⚠️ +3.09 kB
index.pack gzip	73.8 kB	74 kB	⚠️ +215 B
Overall change	2.15 MB	2.16 MB	⚠️ +3.31 kB

Diff details

Diff for main-HASH.js

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Diff for server.runtime.prod.js

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Commit: 8e92870

[unstubbable]

This a nice improvement overall, but showing eval instead of the jsx element name does feel like a small regression.

[eps1lon]

This a nice improvement overall, but showing eval instead of the jsx element name does feel like a small regression.

Yeah, it was accidentally doing the nicer thing. Still wrong though. Just looked more pleasant.