Possible to extend or merge across a union?

Is it possible to extend or merge across a zod union?

The use case I have here is that I have a polymorphic type which I store in a JSON field in my DB where I want to: (a) represent the input I get which does not have an id on it (b) represent what I get from the database, which now has an id on it

I’ve provided an example below - I tried a few other attempts without any luck. Please let me know if there’s a way to do this - thank you!

// example:

const TestThing1 = z.object({
  type: z.literal('thing1'),
  // ... other properties not shared 
});
const TestThing2 = z.object({
  type: z.literal('thing2'),
  // ... other properties not shared 
});
const TestThing3 = z.object({
  type: z.literal('thing3'),
  // ... other properties not shared 
});

const ThingInput = z.union([TestThing1, TestThing2, TestThing3]);

const BaseThing = z.object({
  id: z.string().uuid(),
});
// I want to do something like this, but I get an error (see below)
const Thing = z.union([TestThing1, TestThing2, TestThing3].map(BaseThing.merge));

// Error 
Argument of type 'ZodObject<extendShape<{ id: ZodString; }, { type: ZodLiteral<"thing1">; } | { type: ZodLiteral<"thing2">; } | { type: ZodLiteral<"thing3">; }>, "strip", ZodTypeAny, { ...; }, { ...; }>[]' is not assignable to parameter of type '[ZodTypeAny, ZodTypeAny, ...ZodTypeAny[]]'.
  Source provides no match for required element at position 0 in target.ts(2345)

[jjm340]

To be clear Typescript supports this and it’s awkward in Zod to do this because you have to nest under another key unless there’s a workaround I’m not aware of.

[teddycoleman]

Gotcha, yeah I had a feeling I would need to do something like that. Thanks for taking a look!