[FEATURE] supporting discriminator - openAPI v3

[fordavid]

Is your feature request related to a problem? Please describe.
The api config openAPI v3.0.2 json file I'm using contains discriminators. the code generation build process end up with error message and the generated files are missing the discriminators data.
sample json file that generate the problem attached.

(https://github.com/epam-cross-platform-lab/swagger-dart-code-generator/files/10871982/openapi3.txt)

Is it planned to be supported?

[SEVERE] swagger_dart_code_generator on swagger/.DS_Store (cached):

FileSystemException: Failed to decode data using encoding 'utf-8', path = 'swagger/.DS_Store'
[SEVERE] swagger_dart_code_generator on lib/swagger/.DS_Store (cached):

FileSystemException: Failed to decode data using encoding 'utf-8', path = 'lib/swagger/.DS_Store'
[SEVERE] Failed after 43ms
pub finished with exit code 1

Describe the solution you'd like
see the attached issue
Link to swagger previous request

Swagger specification link
Link to swagger/OpenApi documentation
[openapi3.txt]

[fryette]

Discriminator section from Swagger documentation
https://swagger.io/docs/specification/data-models/inheritance-and-polymorphism/

[nythrox]

There are a few weird ways this could be typed.

Least frightening, oneOf could be typed with a generated class OneOf2<A,B> class OneOf3<A,B, C> class OneOf4<A,B, C,D> etc... and the user can final oneOf = result.body!; if (oneOf.a != null) // a is A.

If you want it to be the most strictly typed possible, every time we encounter a "anyOf": [{$ref: '#/components/schemas/Cat' }, {$ref: '#/components/schemas/Dog'}], we could generate the following classes:

sealed class CatOrDog {}
sealed class CatOrDog_Cat implements CatOrDog, Cat{}
sealed class CatOrDog_Dog implements CatOrDog, Dog  {}

switch (result.body!) { // AnyOfCatDog
   Cat(:name) => ...
   Dog(:age) => ...
}
// Works, checks for exhaustiveness!

We could also just return Object and let the user match on it to type-check.

[dJani97]

This would be great - currently I have to use a different library called dart_mappable for manually modelling those classes that have a discriminator.