Microsoft/TypeScript

Generic syntax ambiguity is handled incorrectly

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#60,874 opened on Dec 29, 2024

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 (1 comment) (1 reaction) (0 assignees)TypeScript (6,726 forks)batch import
BugDomain: ParserHelp Wanted

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Description

🔎 Search Terms

generic syntax ambiguity

🕗 Version & Regression Information

  • I was unable to test this on prior versions because there is no online tooling for it

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAhjAvDAjAGhgIyTATB4HAZgwBMcAWDAUxwFYBuAKFEhABtqA6dkAcwAUCADxYMAwgD4YA8gDIY1AJQrmQA

💻 Code

const a = 1, b = 2, c = 3, d = 4, e = 5;
console.log(a < b, (c > (d & e)));

🙁 Actual behavior

This expression is not callable.

🙂 Expected behavior

true false

Additional information about the issue

While there might be some justification for why

const a = 1, b = 2, c = 3, d = 4, e = 5;
console.log(a < b, c > (d & e));

doesn't work as it did in JS, in the provided example there isn't even any disambiguity.

Contributor guide

Research direction
Investigate the TypeScript parser's handling of the `>` token in expressions when preceded by a generic like context. Trace the parser's behavior for `console.log(a < b, (c > (d & e)));` to understand why it interprets the second argument as a call expression instead of a relational comparison.
Tech stack
typescript
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
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.
30