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Literal strings with generics are inconsistant when strictNullChecks is false #50787
Description
Bug Report
🔎 Search Terms
- string literal
- strictNullChecks
- keyof
🕗 Version & Regression Information
It works properly on v4.7.4 but is failing on v4.8.2 and with the nightly build.
It also works normally when strictNullChecks is true.
⏯ Playground Link
Playground link with relevant code
💻 Code
type Model = { s: string; b: boolean }
let pick: <Keys extends keyof Model>(properties: readonly Keys[]) => Pick<Model, Keys>
let transform: <T>(obj: T) => T
const result1 = transform(pick(["s"]))
const intermediate = pick(["s"])
const result2 = transform(intermediate)🙁 Actual behavior
result1 has a type of Pick<Model, keyof Model> and result2 as a type of Pick<Model, "s">
🙂 Expected behavior
result1 and result2 should have the same type Pick<Model, "s">.
Activity
ahejlsberg commentedon Sep 17, 2022
TypeScript Bot (@typescript-bot) bisect good v4.7.4 bad v4.8.2
ahejlsberg commentedon Sep 17, 2022
Was broken by #49086. Manually bisected to a2b785b.
andrewbranch commentedon Sep 19, 2022
Adding a
T extends {}constraint totransformmakes it repro in--strictNullCheckstoo.andrewbranch commentedon Sep 19, 2022
I added a fix to #50759, which needs a review. It’s the same fix for #50635, but from one additional call site.