Cannot assign type which should be compatible when conditional generics are used

[EnkeyMC]

Bug Report

Cannot assign type which should be compatible when conditional generics are used (also posted on SO but was only suggested to open issue here)

🕗 Version & Regression Information

Throws error on all versions available in TypeScript playground.

Playground Link

⏯ Playground Link

💻 Code

// Returns keyes that have type extending Types
type KeysMatching<T, Types> = { [K in keyof T]: T[K] extends Types ? K : never }[keyof T];

type Mapping = {
    STR: string;
    NUM: number;
    BOOL: boolean;
}

type Values = Mapping[keyof Mapping];

type Generic<T extends Values> = {
    typeStr: KeysMatching<Mapping, T>
}

const foo: Generic<boolean> = { typeStr: 'BOOL' };
const bar: Generic<Values> = foo;
// Type 'Generic<boolean>' is not assignable to type 'Generic<Values>'.
//  Type 'Values' is not assignable to type 'boolean'.
//    Type 'string' is not assignable to type 'boolean'.(2322)

// This works fine
type Conditional<T, V> = T extends V ? T : unknown;
const foo2: Conditional<string, Values> = 'string';
const bar2: Conditional<Values, Values> = foo2;

🙁 Actual behavior

TS throws error that foo is not assignable to bar

🙂 Expected behavior

TS does not throw error as the types should be compatible

[whzx5byb]

A shorter repro:

type V<T> = { value: 0 extends T ? T : never };
type V0 = V<0>; // V0 = { value: 0 }
type VNumber = V<number>; // VNumber = { value: number }

type R1 = V<0> extends V<number> ? true : false;
//   ^?
type R2 = V0 extends VNumber ? true : false
//   ^?

Expect both to be true but R1 is false.

Related: #48070

[fatcerberus]

Probably something to do with variance measurement - it seems like V<T> is incorrectly being measured as contravariant/invariant in T, likely because T occurs on the RHS of an extends check. R2 is correctly determined to be true because V0 extends VNumber bypasses variance measurement and does a full structural check.

[andrewbranch]

Yeah, duplicate of #48070

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.