microsoft / microsoft/TypeScript
Error type on spreading array with additional props
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Bug
Domain: Intersection
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Description
🔎 Search Terms
array intersection spread any
🕗 Version & Regression Information
- This is the behavior in every version I tried
⏯ Playground Link
💻 Code
type withExtraProps = extractArray<{ name: string } & string[]>;
// ^? any[]
type extractArray<t extends readonly unknown[]> = [...{ [i in keyof t]: t[i] }];
🙁 Actual behavior
Inferred as any[] due to an internal error type
🙂 Expected behavior
Inferred as string[]
Additional information about the issue
@Andarist mentioned this could be related to https://github.com/microsoft/TypeScript/issues/59260
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 TypeScript Playground reproduction and compare it with related issue #59260. Trace why extractArray is inferred as any[] rather than string[]; done when the reproduction infers string[] without regressing existing behavior.
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
- 42/100