Omit properties that extends a specific type

Issue

Given the following interface:

interface Entity {
  A: boolean;
  B: string;
  C: number;
  D: never
}

I would like to create a type that omits the properties that extends never. Something like that:

type FilteredEntity = OmitNever<Entity>; //  = { A: boolean; B: string; C: number };

How OmitNever should be implemented?

Solution

Here is how I would solve your problem:

interface Entity {
  A: boolean;
  B: string;
  C: number;
  D: never
}

type Entries<T> = {
  [K in keyof T]: [K, T[K]]
}[keyof T]

type EntriesWithValueOfType<T, U> = T extends [any, U] ? T : never;

type EntityNeverEntries = EntriesWithValueOfType<Entries<Entity>, never>

type KeysOfEntries<T> = T extends [infer U, any] ? U : never;

type OmitNever = Omit<Entity, KeysOfEntries<EntityNeverEntries>>

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Answered By - Guerric P