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Generic property type widened by conditional #28804
Description
TypeScript Version: 3.2.1
Search Terms: generic, conditional type, widened
Code
type A = { foo: "a" }
type B = { foo: "b" }
type C = A | B
type Resolve<T extends "a" | "b"> = "a" | "b" extends T ? never : T
type GenericResolve<T extends C> = Resolve<T["foo"]>
type X = Resolve<"a"> // "a"
type Y = Resolve<A["foo"]> // "a"
type Z = GenericResolve<A> // never
type ResolveWithoutCondition<T extends "a" | "b"> = T
type GenericResolveWithoutCondition<T extends C> = ResolveWithoutCondition<T["foo"]>
type ZZ = GenericResolveWithoutCondition<A> // "a"Expected behavior:
Z should be "a"
Actual behavior:
Z is never
Related Issues:
Could not find any
Activity
jack-williams commentedon Dec 2, 2018
I think this has been fixed by #28718. Try the latest version of master and see if that works.
ahejlsberg commentedon Dec 2, 2018
This is indeed the same issue as #28654 and has been fixed by #28718.
typescript-bot commentedon Dec 12, 2018
This issue has been marked as a duplicate and has seen no activity in the last day. It has been closed automatic house-keeping purposes.