Elementwise elaboration fails to be found for properties mixed with incompatible index signatures using intersections
#58,344 opened on Apr 28, 2024
Repository metrics
- Stars
- (48,455 stars)
- PR merge metrics
- (Avg merge 6d 17h) (9 merged PRs in 30d)
Description
🔎 Search Terms
elementwise elaboration errors write type index signature intersection
🕗 Version & Regression Information
- This is the behavior in every version I tried
⏯ Playground Link
💻 Code
const test: { [k: string]: number } & { foo: string } = { foo: "bar" };
🙁 Actual behavior
test variable gets highlighted
🙂 Expected behavior
I'd expect foo property in the source to get highlighted
Additional information about the issue
I don't really expect this to get any meaningful priority ;p it's just something interesting that I noticed while investigating some legitimate question as to why an error is not on the property itself in a more complex situation. Such intersections are flawed on principle so 🤷♂️
This happens because elaborateElementwise uses getBestMatchIndexedAccessTypeOrUndefined and that prefers concrete properties on intersections over index signatures. The problem is that you can read such dubious properties from the type (and it has a matching type in the example above so it doesn't become an elementwise candidate) but you can't quite write to them.