Infinities as number literal types

🔎 Search Terms

infinity number literal

🕗 Version & Regression Information

• This changed in PR https://github.com/microsoft/TypeScript/pull/55268

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20231031#code/C4TwDgpgBACg9gZwJbCQNwgSQHYDMnYohQC8UAjBAJw0DcAUAPSNSsB6A-PaJFAHIQA5gENUGHPkKhSUALSUaVBs1ZRO9IA

💻 Code

type PositiveInfinity = 1e999;
//   ^?
type NegativeInfinity = -1e999;
//   ^?

🙁 Actual behavior

In TS 5.2 we get NumberLiteralTypes with Infinity and -Infinity values.

In the upcoming TS 5.3 we get a number type in the of the PositiveInfinity

🙂 Expected behavior

I don't know. I created this issue to discuss exactly that.

Should this part of the change be reverted and should Infinity be allowed as a literal number value? Or should -Infinity be aligned with Infinity and should it be converted~ to a number type as well?

Additional information about the issue

I didn't see an Infinity as a literal type so I made this change while working in this area. @rbuckton commented here:

I really hope no one is relying on this.

but it turns out that some try to rely on this. We can see it in this issue, cc @Max10240

Start with the linked Playground example and compare the TypeScript 5.2 behavior with the upcoming 5.3 behavior introduced by PR 55268. Review the discussion in that pull request and issue 56270, then establish the intended treatment of positive and negative infinity before changing the compiler behavior and its regression coverage.