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Parse `for await (async of ...)` by Zalathar · Pull Request #13244 · babel/babel · GitHub
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Parse for await (async of ...) - #13244

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nicolo-ribaudo merged 7 commits into
babel:mainfrom
Zalathar:async-arrow-lookahead
May 1, 2021
Merged

Parse for await (async of ...)#13244
nicolo-ribaudo merged 7 commits into
babel:mainfrom
Zalathar:async-arrow-lookahead

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@Zalathar

@Zalathar Zalathar commented May 1, 2021 •
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Q                       A
Fixed Issues? Fixes #13235
Patch: Bug Fix? Yes
Major: Breaking Change? No
Minor: New Feature? No
Tests Added + Pass? Yes
Documentation PR Link
Any Dependency Changes? No
License MIT

This allows the parser to correctly parse for await (async of []); by implementing the suggestion given by @JLHwung in #13235 (comment).

When the expression parser sees async of, it will peek ahead for a = character before it commits to parsing an async arrow function.

On its own this would also cause for (async of []); to parse, which is forbidden, so we also add explicit code to the for parser to detect and reject for-of statements that begin with async of.

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babel-bot commented May 1, 2021 •
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Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/45770/

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JLHwung
JLHwung reviewed May 1, 2021
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Comment thread packages/babel-parser/src/parser/statement.js Outdated
@nicolo-ribaudo nicolo-ribaudo added the PR: Bug Fix 🐛 A type of pull request used for our changelog categories label May 1, 2021
JLHwung
JLHwung reviewed May 1, 2021
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Comment thread packages/babel-parser/test/fixtures/core/categorized/for-async-of-dot/input.js
@Zalathar

Zalathar commented May 1, 2021

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Is there any particular place I should be putting these parser tests? I wasn't sure if I should put them in es2015/for-of/.

@Zalathar
Zalathar force-pushed the async-arrow-lookahead branch from 2479882 to 3890721 Compare May 1, 2021 14:45
@JLHwung

JLHwung commented May 1, 2021

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@Zalathar The for(async of tests can be placed in es2021, resulted from a need-Consensus PR: tc39/ecma262#2256

The for await(async of tests can be placed in es2018/async-generators. The syntax hasn't changed since then.

JLHwung
JLHwung approved these changes May 1, 2021
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Awesome!

@Zalathar
Zalathar force-pushed the async-arrow-lookahead branch from 3890721 to cc7e470 Compare May 1, 2021 14:58
nicolo-ribaudo
nicolo-ribaudo approved these changes May 1, 2021
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Thanks!

@nicolo-ribaudo nicolo-ribaudo changed the title Parse for await (async of by adding lookahead to unary async arrow parsing Parse for await (async of ...) May 1, 2021
@nicolo-ribaudo
nicolo-ribaudo merged commit fa01fbe into babel:main May 1, 2021
@Zalathar
Zalathar deleted the async-arrow-lookahead branch May 1, 2021 16:11
@Zalathar Zalathar mentioned this pull request May 5, 2021
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@github-actions github-actions Bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Aug 1, 2021
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@JLHwung JLHwung JLHwung approved these changes
@nicolo-ribaudo nicolo-ribaudo nicolo-ribaudo approved these changes

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[Bug]: Parser can't parse "for await (async of []);"

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@Zalathar @babel-bot @JLHwung @nicolo-ribaudo