Merge two types, overlapping part use union

ComposeSharp.ts

type IsPartial<T> = T extends Required<T> ? false : true;
type NoPartial<Sharp1, Sharp2> = IsPartial<Sharp1> & IsPartial<Sharp2> extends true ? false : true;
// Merge two types, overlapping part use union
export type ComposeSharp<
  Sharp1,
  Sharp2,
  InterKeys extends keyof Sharp1 & keyof Sharp2 = keyof Sharp1 & keyof Sharp2
> = UnionToIntersection<
  InterKeys extends unknown
    ? NoPartial<Pick<Sharp1, InterKeys>, Pick<Sharp2, InterKeys>> extends true
      ? Record<InterKeys, Sharp1[InterKeys] | Sharp2[InterKeys]>
      : Partial<Record<InterKeys, Sharp1[InterKeys] | Sharp2[InterKeys]>>
    : never
> &
  Pick<Sharp1, Exclude<keyof Sharp1, InterKeys>> &
  Pick<Sharp2, Exclude<keyof Sharp2, InterKeys>>;

// test cases
type A = { a: 1; b: 2 };
type B = { a: 2; c: 3 };
type C = { a?: 3; d: 4 };
type D = { a?: 4; e: 5 };
type Test1 = ComposeSharp<A, B> extends { a: 1 | 2; b: 2; c: 3 } ? true : false; // true
type Test2 = ComposeSharp<C, D> extends { a?: 3 | 4; d: 4; e: 5 } ? true : false; // true
type Test3 = ComposeSharp<A, C> extends { a?: 1 | 3; b: 2; d: 4 } ? true : false; // true
const test1: Test1 & Test2 & Test3 = true;