Example of descriptive type errors instead of `never`s

TypesError.ts

declare const errorTag: unique symbol;
type TypesError<T> = { [errorTag]: T };
interface Validatable {
    validate(): boolean;
}
type Assert<T, TType, TTypeName extends string, TTargetName extends string = string, TSource extends string = string> = T extends TType ? T :
    string extends TTargetName
    ? TypesError<`T should be of type {${TTypeName}}`>
    : string extends TSource
    ? TypesError<`{${TTargetName}} should be of type {${TTypeName}}`>
    : TypesError<`{${TTargetName}} in {${TSource}} should be of type {${TTypeName}}`>;

type Assert_acceptValidatable<T> = Assert<T, Validatable, "Validatable", "target", "acceptValidatable(target)">
function acceptValidatable<T>(target: T): Assert_acceptValidatable<T> {
    return target as Assert_acceptValidatable<T>;
}

const res = acceptValidatable({ validate: () => 'string' });
//    ^?
// TypesError<`{target} in {acceptValidatable(target)} should be of type {Validatable}`>