Switch to `@jridgewell/gen-mapping` for sourcemap generation #14497

jridgewell · 2022-04-27T02:16:34Z

Q	A
Fixed Issues?	Closes #12805
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	Yes, removed final `source-map` and switch to `@jridgewell/gen-mapping`
License	MIT

This removes the final use (of an ancient version 5yo version) of source-map. This gives a few benefits:

Adding mappings to the sourcemap is ~30-300% faster.
Serializing the map for writing is 250-550% faster
Preparing a map for merging is free, and actual merging is 5-25x (x, not %) faster

Somewhat controversial, but I'm making rawMappings slower. Why? Because it isn't used by anyone. And, we're always generating a map output (because babel-cli reads the .map getter). I think it's more important to prioritize the regular sourcemap than the rawMappings. If someone wants to use rawMappings for speed, I'd encourage them to use the new decodedMap field, and @jridgewell/trace-mapping to trace or @ampproject/remapping to remap. Regardless, adding items to the GenMapping should be just as fast as pushing items onto the _rawMappings, and possibly considerably faster since the raw mappings covers every line/column vs the gen-mapping's per-line array.

babel-bot · 2022-04-27T02:19:49Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/51761/

nicolo-ribaudo

Awesome, thanks! 😄

nicolo-ribaudo · 2022-04-27T08:23:12Z

packages/babel-cli/test/fixtures/babel/dir --out-dir --source-maps/out-files/lib/foo.js.map

@@ -1 +1 @@
-{"version":3,"sources":["../src/foo.js"],"names":["arr","map","x","MULTIPLIER"],"mappings":";;AAAAA,GAAG,CAACC,GAAJ,CAAQ,UAAAC,CAAC;AAAA,SAAIA,CAAC,GAAGC,UAAR;AAAA,CAAT","sourcesContent":["arr.map(x => x * MULTIPLIER);"],"file":"foo.js"}
+{"version":3,"file":"foo.js","names":["arr","map","x","MULTIPLIER"],"sources":["../src/foo.js"],"sourcesContent":["arr.map(x => x * MULTIPLIER);"],"mappings":";;AAAAA,GAAG,CAACC,GAAJ,CAAQ,UAAAC,CAAC;AAAA,SAAIA,CAAC,GAAGC,UAAR;AAAA,CAAT"}


For reviewers: the various source map changes are just differences in the fields order; the contents are the same.

nicolo-ribaudo · 2022-04-27T08:25:24Z

packages/babel-generator/src/source-map.ts

      source:
        line == null
          ? undefined
-          : (filename || this._opts.sourceFileName).replace(/\\/g, "/"),
+          : filename?.replace(/\\/g, "/") || this._sourceFileName,


For reviewers: this._sourceFileName is already normalized in the constructor.

nicolo-ribaudo · 2022-04-27T08:29:57Z

The Jest failures are caused by this PR, because of #14497 (comment). We can let them fail until the next patch, so that Jest can then update their snapshots.

jridgewell · 2022-04-27T12:19:36Z

Given this is causing breaking changes in downstream projects, we can preserve the prop ordering of the sourcemap pretty easily. I'll push a commit.

nicolo-ribaudo · 2022-04-27T12:53:56Z

I mean, I wouldn't consider it a breaking change but just a "testing implementation details". The order of object keys is never considered part of the "public contract" 😛

It's enough to let @SimenB know about this so that he won't be surprised about the Jest failures when updating Babel, and we don't need to worry about preserving the original properties order.

SimenB · 2022-04-27T13:02:39Z

Hey! 👋

Exciting to see more of source-map modernized (replaced) 👏

I totally agree key order shouldn't be part of the contract - will update our snapshots once there's a release 🙂

(you can probably just delete the test in the meantime in your e2e test if you want it green)

This reverts commit accb758.

JLHwung

🥳

[`gen-mapping`](https://github.com/jridgewell/gen-mapping) is faster, smaller, and lighter sourcemap generation library. This also exposes a new `decodedMap` property on the result object. Decoded maps are free to create (it's a shallow clone of the `GenMapping` instance), and passing them to `@jridgewell/trace-mapping` is copy-free. With Babel [recently](babel/babel#14497) adding a `decodedMap` field, a dev could pass from the Babel transpilation to Terser without any added memory use for sourcemaps. And if there's a multi stage build process, a dev could use `@ampproject/remapping` to remap Babel, Terser, and (eg) a bundler's outputs without having to feed input maps into each stage.

* Switch to GenMapping for sourcemap generation [`gen-mapping`](https://github.com/jridgewell/gen-mapping) is faster, smaller, and lighter sourcemap generation library. This also exposes a new `decodedMap` property on the result object. Decoded maps are free to create (it's a shallow clone of the `GenMapping` instance), and passing them to `@jridgewell/trace-mapping` is copy-free. With Babel [recently](babel/babel#14497) adding a `decodedMap` field, a dev could pass from the Babel transpilation to Terser without any added memory use for sourcemaps. And if there's a multi stage build process, a dev could use `@ampproject/remapping` to remap Babel, Terser, and (eg) a bundler's outputs without having to feed input maps into each stage. * Apply suggestions from code review Co-authored-by: Fábio Santos <fabiosantosart@gmail.com> * Fix dependency * Switch to source-map compatible @jridgewell/source-map This preserves API compatibility, so that loading source-map in the browser is still supported. * Update TS types * Support source-map's async SourceMapConsumer * Fix sourcesContent check with source-map's SourceMapGenerator Co-authored-by: Fábio Santos <fabiosantosart@gmail.com>

jridgewell added 2 commits April 26, 2022 12:07

Switch to GenMapping to generate source maps

ae288ac

Update to gen-mapping v0.1.0

f814fb6

jridgewell added 2 commits April 26, 2022 23:07

Fix types

1713327

Fix types

6163af9

jridgewell changed the title ~~Gen mapping~~ babel-generator: Switch to @jridgewell/gen-mapping for sourcemap generation Apr 27, 2022

jridgewell changed the title ~~babel-generator: Switch to @jridgewell/gen-mapping for sourcemap generation~~ babel-generator: Switch to gen-mapping for sourcemap generation Apr 27, 2022

jridgewell added pkg: generator PR: New Dependency PR: Performance 🏃‍♀️ A type of pull request used for our changelog categories labels Apr 27, 2022

nicolo-ribaudo approved these changes Apr 27, 2022

View reviewed changes

Preserve legacy prop ordering in sourcemaps

accb758

jridgewell force-pushed the gen-mapping branch from 6403ec7 to accb758 Compare April 27, 2022 12:36

Revert "Preserve legacy prop ordering in sourcemaps"

6c6bb66

This reverts commit accb758.

JLHwung approved these changes Apr 28, 2022

View reviewed changes

nicolo-ribaudo changed the title ~~babel-generator: Switch to gen-mapping for sourcemap generation~~ Switch to @jridgewell/gen-mapping for sourcemap generation Apr 28, 2022

nicolo-ribaudo merged commit b6d8434 into babel:main Apr 28, 2022

jridgewell deleted the gen-mapping branch April 28, 2022 21:40

SimenB mentioned this pull request Apr 30, 2022

chore: update babel jestjs/jest#12780

Merged

Parnassius mentioned this pull request Apr 30, 2022

Babel 7.17.10 breaks build smogon/pokemon-showdown-client#1968

Closed

jridgewell mentioned this pull request Apr 30, 2022

Switch to GenMapping for sourcemap generation terser/terser#1190

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jridgewell mentioned this pull request May 9, 2022

wg-performance Status Update 2022-05-09 ampproject/wg-performance#112

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github-actions bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Jul 29, 2022

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Switch to `@jridgewell/gen-mapping` for sourcemap generation #14497

Switch to `@jridgewell/gen-mapping` for sourcemap generation #14497

jridgewell commented Apr 27, 2022 •

edited by nicolo-ribaudo

babel-bot commented Apr 27, 2022 •

edited

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nicolo-ribaudo Apr 27, 2022 •

edited

nicolo-ribaudo Apr 27, 2022

nicolo-ribaudo commented Apr 27, 2022

jridgewell commented Apr 27, 2022

nicolo-ribaudo commented Apr 27, 2022 •

edited

SimenB commented Apr 27, 2022 •

edited

JLHwung left a comment

		@@ -1 +1 @@
		{"version":3,"sources":["../src/foo.js"],"names":["arr","map","x","MULTIPLIER"],"mappings":";;AAAAA,GAAG,CAACC,GAAJ,CAAQ,UAAAC,CAAC;AAAA,SAAIA,CAAC,GAAGC,UAAR;AAAA,CAAT","sourcesContent":["arr.map(x => x * MULTIPLIER);"],"file":"foo.js"}
		{"version":3,"file":"foo.js","names":["arr","map","x","MULTIPLIER"],"sources":["../src/foo.js"],"sourcesContent":["arr.map(x => x * MULTIPLIER);"],"mappings":";;AAAAA,GAAG,CAACC,GAAJ,CAAQ,UAAAC,CAAC;AAAA,SAAIA,CAAC,GAAGC,UAAR;AAAA,CAAT"}

Switch to @jridgewell/gen-mapping for sourcemap generation #14497

Switch to @jridgewell/gen-mapping for sourcemap generation #14497

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Switch to `@jridgewell/gen-mapping` for sourcemap generation #14497

Switch to `@jridgewell/gen-mapping` for sourcemap generation #14497

jridgewell commented Apr 27, 2022 •

edited by nicolo-ribaudo

babel-bot commented Apr 27, 2022 •

edited

nicolo-ribaudo Apr 27, 2022 •

edited

nicolo-ribaudo commented Apr 27, 2022 •

edited

SimenB commented Apr 27, 2022 •

edited