Vet error for new discriminator of union as enum

[tadelesh]

See example.
The discriminator models will be generated something like:

type Base struct {
    Kind: *Kind
}

type K struct {
    Kind *string
    Name *string
}

func (p *K) GetBase() *Base{
    return &Base{
        Kind: p.Kind,
    }
}

Since the kind is an open enum, it is possible that the model's kind property has a name not in the enum value list, which means the discriminator property type should not be the enum type.

[jhendrixMSFT]

This is how extensible enums works. Any value not in the list can still be supported via a cast. It's unclear why we'd change it at this point, can you clarify?

[tadelesh]

Pending on final decision of open/close enum of TypeSpec.

[tadelesh]

should be fixed tcgc