Recursive mapped conditional types not working when using interfaces (regression between 3.3.3 and 3.5.1)

[ItsaMeTuni]

Bug Report

🔎 Search Terms

recursive mapped conditional types interface generic

🕗 Version & Regression Information

• This changed between versions 3.3.3 and 3.5.1

⏯ Playground Link

Playground link with relevant code (version 3.3.3, working as intended)

Playground link with relevant code (version 3.5.1, breaking)

💻 Code

interface Data {
    rootValue: number;
    nested: {
        nestedValue: string;
    }
}

// Problem lies here
type Test<T> = {
    [K in keyof T]: T extends Record<string, unknown> ? Test<T[K]> : false;
};

// When using an interface, the mapped type for the nested field is incorrect
type WithInterface = Test<Data>;
type NestedInWithInterface = WithInterface['nested']; // false

// However when using a type directly it works as intended
type WithPlain = Test<{
    rootValue: number;
    nested: {
        nestedValue: string;
    }
}>;
type NestedInWithPlain = WithPlain['nested']; // { nestedVaue: string }


// Using a type instead of an interface also works as intended
type DataType = {
    rootValue: number;
    nested: {
        nestedValue: string;
    }
}

type WithType = Test<DataType>;
type NestedInWithType = WithType['nested']; // { nestedVaue: string }


// And using another mapped type that's just an identity of the input also works
type Identity<T> = {
    [K in keyof T]: T[K]
}

type WithInterfaceIdentity = Test<Identity<Data>>;
type NestedInWithInterfaceIdentity = WithInterfaceIdentity['nested']; // { nestedVaue: string }

🙁 Actual behavior

When using a recursive mapped conditional type (not sure if I named it correctly), typescript breaks when using an interface as the generic parameter, but works when using inline types, type aliases and a mapped type.

🙂 Expected behavior

Expected NestedInWithInterface to be { nestedVaue: string }, just like NestedInWithPlain, NestedInWithType, and NestedInWithInterfaceIdentity.

[whzx5byb]

See #50087 (comment)

[ItsaMeTuni]

See #50087 (comment)

Of course! It makes total sense, I can't believe I missed that and spent hours debugging this... Sorry about the trouble and thanks for the quick response.