Generic syntax ambiguity is handled incorrectly

[reverofevil]

🔎 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.

[robpalme]

The general Relational Expression ambiguity is a long-standing known issue. But as you mention, this is a more specific case where there's no ambiguity given that < b, (c > cannot be parsed as type arguments.

Whilst the TypeScript parser deems < b, (c > to be erasable types, most other mainstream parsers do not. These parsers correctly preserve the original JS semantics when attempting to parse as TS:

• Babel
• esbuild
• Oxc
• SWC