Incorrect Merge with optional any fields

[center-777]

Hi!

First of all, sorry for my english 🤷‍♂️

I found a problem with incorrect merging of types with optional any fields.
Tested on version 3.7.0.

Current Merge type is:

type Merge<Destination, Source> = EnforceOptional<
    SimpleMerge<PickIndexSignature<Destination>, PickIndexSignature<Source>>
    & SimpleMerge<OmitIndexSignature<Destination>, OmitIndexSignature<Source>>>;

and next code gives us type with all required fields:

type DestinationWithOptionalAnyKeys = {
	a?: any;
	c: string;
	d?: any;
	e: number;
};
type SourceWithOptionalAnyKeys = {
	b?: any;
	c?: any;
	d: number;
};
type DestinationSourceWithOptionalAnyKeys = Merge<DestinationWithOptionalAnyKeys, SourceWithOptionalAnyKeys>;

declare const destinationSourceWithOptionalAnyKeys: DestinationSourceWithOptionalAnyKeys;
// destinationSourceWithOptionalAnyKeys => {
//      a: any,
//      b: any,
//      c: any,
//      d: number,
//      e: number
//  }

The problem is that the Merge try set optional fields with EnforceOptional, which makes optional only * | undefined fields.
But fields with any other types will stay required.

So, if we rewrite Merge type as:

type Merge<Destination, Source> =
    EnforceOptional<
        // At this point we set all fields except required as optional
        SetOptional<
            SimpleMerge<PickIndexSignature<Destination>, PickIndexSignature<Source>>
            & SimpleMerge<OmitIndexSignature<Destination>, OmitIndexSignature<Source>>,
            Exclude<
                OptionalKeysOf<PickIndexSignature<Destination> & OmitIndexSignature<Destination>>
                | OptionalKeysOf<PickIndexSignature<Source> & OmitIndexSignature<Source>>,
                RequiredKeysOf<PickIndexSignature<Source> & OmitIndexSignature<Source>>>>>;

we will get the correct result:

// destinationSourceWithOptionalAnyKeys => {
//     d: number,
//     e: number,
//     a?: any,
//     b?: any,
//     c?: any
// }

It solves a problem with optional any type fields, but gives "Type instantiation is excessively deep and possibly infinite" error at MergeDeep type in tests:

Variables fooBarTupleSpread and fooBarTupleReplace casts to any type because of this error.

Does anyone have any ideas, how can i fix it?

[david-crespo]

I think this is a duplicate of #506, or at least related