Invalid declarations for inlined distributive types in 4.7

[dragomirtitian]

Bug Report

🔎 Search Terms

invalid declaration distributive types

🕗 Version & Regression Information

• This changed between versions 4.6 and 4.7

⏯ Playground Link

Workbench

Playground Link For resulting declarations

💻 Code

// @filename: types.ts
type Fns =  Record<string, (...params: unknown[]) => unknown>

type Map<T extends Fns> = { [K in keyof T]: T[K]; };

type AllArg<T extends Fns> = { [K in keyof T]: Parameters<T[K]> };

function fn<T extends { x: Map<T['x']> }>(sliceIndex: T): AllArg<T['x']> {
    return null!;
}

export default { fn };

// @filename: reexport.ts

import test from "./types";
export default { test };

🙁 Actual behavior

TypeScript generates this declaration:

declare const _default: {
    test: {
        fn: <T_1 extends {
            x: T_1["x"] extends infer T ? { [K in keyof T]: T_1["x"][K]; } : never;
        }>(sliceIndex: T_1) => T_1["x"] extends infer T_2 ? { [K_1 in keyof T_2]: Parameters<T_1["x"][K_1]>; } : never;
    };
};
export default _default;

In the declaration above the expression Parameters<T_1["x"][K_1]> doesn't type check. The T_1["x"] is not constrained anymore to be Record<string, (...params: unknown[]) => unknown>

TypeScript could include the constraint of the original type in the declaration:

declare const _default: {
    test: {
        fn: <T_1 extends {
            x: T_1["x"] extends (infer T extends Record<string, (...params: unknown[]) => unknown>) ? { [K in keyof T]: T_1["x"][K]; } : never;
        }>(sliceIndex: T_1) => T_1["x"] extends (infer T_2 extends Record<string, (...params: unknown[]) => unknown>)
             ? { [K_1 in keyof T_2]: Parameters<T_1["x"][K_1]>; } : never;
    };
};
export default _default;

🙂 Expected behavior

Resulting declarations for reexport.ts are valid

[MartinJohns]

Possibly related? #49572