Intent to Extend Experiment: Explicit Compile Hints with Magic Comments

[Marja Hölttä]

Contact emails

ma...@google.com, les...@google.com

Explainer

https://github.com/explainers-by-googlers/explicit-javascript-compile-hints-file-based/blob/main/README.md

Specification

None

Summary

Allow attaching information about which functions should be eager parsed & compiled in JavaScript files. The information will be encoded as magic comments. We'll first target launching the file-based explicit compile hints, and as a follow up, investigate selecting individual functions for eager compilation.

Blink component

Blink>JavaScript

TAG review

TAG review status

Pending

Chromium Trial Name

JavaScriptCompileHintsMagic

Link to origin trial feedback summary

https://google.qualtrics.com/jfe/form/SV_9SLyOGnTj2cwo0C

Origin Trial documentation link

https://docs.google.com/document/d/19xTAM4A75tz0xUq_velMzGA4JHEgXpyflUxXTcuNiyE/edit?usp=sharing

Risks

Interoperability and Compatibility

No interoperability / compatibility risks. Other browsers are likely to ignore the hints if they perceive they cannot benefit from them. Ignoring the hint is allowed behavior. We plan to make the hints generic though, so that other browsers can later start to support them too, e.g., if they implement background parsing / compilation.

Gecko: N/A (https://github.com/mozilla/standards-positions/issues/780)

WebKit: N/A (https://github.com/WebKit/standards-positions/issues/172)

Web developers: Positive Positive signals from partners who want to use compile hints to eager-compile core JS files.

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

Goals for experimentation

We'd like to measure the performance of the improved feature implementation in userland partner metrics.

Reason this experiment is being extended

The origin trial configuration for this feature was broken in M115-M116, and the users weren't able to run the experiments.

Reason this experiment is being extended

We did an origin trial in versions 115-117. We modified the feature based on the results (performance measurements by Google Workspace) and we'd now like to do another origin trial with the modified feature, in versions 129-131.

Ongoing technical constraints

Debuggability

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

No

The feature doesn't trigger any functional changes and cannot be tested by WPT.

Flag name on chrome://flags

Finch feature name

None

Non-finch justification

None

Requires code in //chrome?

False

Tracking bug

https://bugs.chromium.org/p/v8/issues/detail?id=13917

Estimated milestones

Origin trial desktop first	115
Origin trial desktop last	117
Origin trial extension 1 end milestone	120
Origin trial extension 2 end milestone	131

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5100466238652416?gate=5198754872819712

Links to previous Intent discussions

Intent to Experiment: https://groups.google.com/a/chromium.org/g/blink-dev/c/BmN1Wus8V1s/m/3L2uU-wGAgAJ
Intent to Extend Experiment 1: https://groups.google.com/a/chromium.org/g/blink-dev/c/BmN1Wus8V1s/m/rhtpXTyPCgAJ

This intent message was generated by Chrome Platform Status.

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[Mike Taylor]

Just to clarify: this ran as an OT from 115 to 117, and has been disabled since then?

And you're requesting to run another OT (vs extending a currently active one) from 129 to 131.

Do I have that correct?

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[Marja Hölttä]

Yes, the OT expired and I'd like to run a new one. There was no way to input the "beginning milestone number" for the extension in Chromestatus.

[Mike Taylor]

Thanks for the clarification. LGTM to (re-)run 129 to 131 inclusive.