microsoft / microsoft/TypeScript
Index type for an intersected `NoInfer` can get sometimes incorrectly deferred
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Domain: Index Types
Help Wanted
Possible Improvement
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- Go
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Description
🔎 Search Terms
noinfer intersection index type keyof deferred deferral
🕗 Version & Regression Information
- This is the behavior in every version I tried
⏯ Playground Link
💻 Code
type Test = keyof (NoInfer<{ foo: string }> & {});
// ^? type Test = keyof (NoInfer<{ foo: string; }> & {})
type Test2 = keyof ({ foo: string } & {});
// ^? type Test2 = "foo"
🙁 Actual behavior
Test is a deferred index type
🙂 Expected behavior
Test shouldn't be a deferred index type but a "foo" literal, just like Test2.
Additional information about the issue
No response
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 and reproduce the Test and Test2 aliases from the issue. Trace how the type checker handles keyof over an intersection containing NoInfer; done means Test resolves to the "foo" literal instead of a deferred index type, matching Test2.
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
- 45/100