can discriminator be optional ?

[qiaozha]

Not sure if it's a bug or intentional, in the below case, public typespec playground link

@discriminator("kind")
model Pet {
  name: string;
  weight?: float32;
}

the OpenAPI3 emitter output, will not put kind into required list

    Pet:
      type: object
      required:
        - name
      properties:
        name:
          type: string
        weight:
          type: number
          format: float
        kind:
          type: string
          description: Discriminator property for Pet.
      discriminator:
        propertyName: kind

However, in swagger emitter, it will put kind into the required list, see azure playground link.
But on the other hand, we also have test cases in cadl ranch to testify missing discriminator's case cadl ranch link.

If it's intentional, I wonder why? if it's not, I am curious why we should allow discriminator decorator on a property that doesn't exist ?

/cc @xirzec

[timotheeguerin]

We did have some discussion about that, more when a discriminated union gets used in json merge patch where technically it could allow an optional discriminator.

What you are seeing though is a bug but also I think we want people to move awayt from the implicit discriminator property(where we magically inject it) See this issue #2589

[markcowl]

Once the linting rule is added to require the discriminator to be specified: Azure/typespec-azure#97 this should be resolved, so closing as duplicate