Microsoft/TypeScript

Parse error when using `in` nested in a `for` initializer

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#59,236 opened on Jul 11, 2024

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BugDomain: ParserHelp Wanted

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Description

🔎 Search Terms

in for in init syntax error

🕗 Version & Regression Information

  • This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.5.3#code/GYewTgBAFAbghpOEC8EDaAjCBLAdhAYwF0BuEgShKA

💻 Code

for (var a = [b in c];;);

🙁 Actual behavior

It says "',' expected." at the in

🙂 Expected behavior

It should parse it properly

Additional information about the issue

No response

Contributor guide

Research direction
Look at the TypeScript parser code for 'for' statements, specifically how 'in' is handled in the initializer. Check test cases to understand the expected behavior.
Tech stack
typescript
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65