microsoft / microsoft/TypeScript
Services for non-homomorphic mapped type
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Domain: LS: Symbol Navigation
Domain: Mapped Types
Experience Enhancement
Help Wanted
Suggestion
- Dominant language
- Go
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- Avg merge
- 2d 4h
- Merged PRs (30d)
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Description
TypeScript Version: 3.0.0-dev.20180712
Code
interface I {
a: number;
b: number;
}
type J = { [K in "b"]: I[K] };
declare const j: J;
j.b; // Go-to-definition does not work
Expected behavior:
Since the type we're getting is I[K], the mapped property symbol should have a reference back to the corresponding property in I.
Actual behavior:
The mapped type creates an unrelated property symbol and services don't work.
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 by reproducing the provided mapped-type example and tracing how the mapped property symbol is created for I[K]. Follow the go-to-definition service from j.b and add a regression test showing that it resolves to the corresponding property in I; done means the service works for this case.
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