### Describe the bug A const declaration whose annotated type is a variant of a union cannot be assigned to. This arises in the context of creating const declarations for discriminated unions where the discriminator field is a union. ### Reproduction https://typespec.io/playground/?e=%40typespec%2Fopenapi3&c=bmFtZXNwYWNlIEV4YW1wbGU7DQoNCnVuaW9uIFNwZWNpZXMgew0KICAgIGNhdDogImNhdCINCn3EJi8vIEVycm9yOiBUeXBlICfFHCcgaXMgbm90IGFzc2lnbmFibGUgdG8gdMsixC7EXCh1bsolKQ0KY29uc3QgZeYAiFZhbHVlOugAhC5jYXQgPcwOOw%3D%3D&options=%7B%7D&vs=%7B%7D ### Checklist - [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md) - [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate. - [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions). - [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.
Describe the bug
A const declaration whose annotated type is a variant of a union cannot be assigned to.
This arises in the context of creating const declarations for discriminated unions where the discriminator field is a union.
Reproduction
https://typespec.io/playground/?e=%40typespec%2Fopenapi3&c=bmFtZXNwYWNlIEV4YW1wbGU7DQoNCnVuaW9uIFNwZWNpZXMgew0KICAgIGNhdDogImNhdCINCn3EJi8vIEVycm9yOiBUeXBlICfFHCcgaXMgbm90IGFzc2lnbmFibGUgdG8gdMsixC7EXCh1bsolKQ0KY29uc3QgZeYAiFZhbHVlOugAhC5jYXQgPcwOOw%3D%3D&options=%7B%7D&vs=%7B%7D
Checklist