Merge an union of objects with different types for the same properties

merge.ts

type AllKeys<T> = T extends unknown ? keyof T : never
// type Idx<T, K extends PropertyKey> = T extends any ? T[K & keyof T] : never
type Idx<T, K extends PropertyKey> = T extends unknown ? K extends keyof T ? T[K] : never : never;
type MyMerge<T> = { [K in AllKeys<T>]: Idx<T, K> }

// TODO: result of test case must be `{foo: 1 | 2; bar: 3}`
type TestCase1 = MyMerge<{ foo: 1 } | { foo: 2; bar: 3 }>;

// TODO: result of test case must be `{foo: 1 | 2 | 7; bar: 3 | 8}`
type TestCase2 = MyMerge<
	{ foo: 1 } | { foo: 2; bar: 3 } | { foo: 7; bar: 8 }
>;

// TODO: result of test case must be `{foo: 1 | 2; bar: 3 | 8}`
type TestCase3 = MyMerge<
	{ foo: 1 } | { foo: 2; bar: 3 } | { bar: 8 }
>;