Reproduction
type Generic<Type extends string> = Type;
type GenericInstance = Generic<any>;
type T1 = GenericInstance extends Generic<infer T> ? T : never; // any
type T2 = IsAny<T1>; // true, as it should be
type T3 = GenericInstance extends Generic<infer T> ? IsAny<T> : never; // false, but should be true
// I guess the second inference removes references to the type being a string?
type T4 = GenericInstance extends Generic<infer T> ? IsAny<T extends (infer TT) ? TT : never> : never; // true, as it should beMy wild guess is that it has something to do with the generic constraint <Type extends string> and the returned any is still seen as some sort of string in this case, might be a TS bug?
sindresorhus / type-fest
A collection of essential TypeScript types
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