microsoft / microsoft/TypeScript
Inference from rest parameters has strange inconsistent results
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Description
declare function foo(...x: readonly any[]): any
type FooParams = Parameters<typeof foo>;
declare function bar(...x: readonly number[]): any
type BarParams = Parameters<typeof bar>
Expected:
FooParamsisany[]orreadonly any[]BarParamsisnumber[]orreadonly number[]
Actual
FooParamsisunknown[]BarParamsisnever
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the linked TypeScript Playground reproduction and compare the inferred types of FooParams and BarParams with the stated expected results. Trace the type inference involved in Parameters applied to readonly rest parameters. Done means the two examples produce an accepted expected form and have regression coverage.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100