[ID] --isolatedDeclarations disallows const initialized with a regex literal

[Conaclos]

🔍 Search Terms

• isolatedDeclarations
• isolated declaration

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

I an unsure if it is a bug or a feature request...

An exported const without type annotation and initialized with a regex literal triggers the following error error TS9010: Variable must have an explicit type annotation with --isolatedDeclarations. in isolated declaration mode.

If I understand correctly, isolated declaration should allow unannotated const initialized with any literal?

📃 Motivating Example

See an example on the playground.

💻 Use Cases

This could avoid a trivial type annotation.

[jakebailey]

This would require us to hardcode the type of a regex expression, no? Since regexes aren't an intrinsic and aren't valid initializers in dts?

I guess it could always just be RegExp, so long as that type name hasn't been reused. It's not like "number" or a literal value where the type name is reserved.

[RyanCavanaugh]

This seems like the same situation as any other literal type, except that regex literal types don't exist, so we can safely write X: RegExp (yeah, barring shadowing)

[jakebailey]

Just hope we never add stricter RegExp types...

Does the quick fix at least suggest adding : RegExp in the latest nightly?

[jakebailey]

The fix does work, so this issue is mainly about whether or not ID should allow this inference.