When the initial element of the tuple is a rest element, it is not possible to correctly infer the type of the initial element. #56885
Description
🔍 Search Terms
initial element of the tuple is a rest element
✅ 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
type T1 = [...string[], number, boolean]
declare const head: T1[0]
// Actual: string | number | boolean
// Expected: string | number