Openapi-generator: [BUG][typescript-fetch] withInterfaces option does not generate interfaces

[fuzzzerd]

Bug Report Checklist

• [x] Have you provided a full/minimal spec to reproduce the issue?
• [x] Have you validated the input using an OpenAPI validator (example)?
• [x] What's the version of OpenAPI Generator used?
• [x] Have you search for related issues/PRs?
• [x] What's the actual output vs expected output?
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Description

Compare these files in the samples directory:

https://github.com/OpenAPITools/openapi-generator/blob/master/samples/client/petstore/typescript-fetch/builds/default/apis/PetApi.ts

vs

https://github.com/OpenAPITools/openapi-generator/blob/master/samples/client/petstore/typescript-fetch/builds/with-interfaces/apis/PetApi.ts

openapi-generator version

Master branch

Suggest a fix

Could not find reference to withInterfaces parameter in the mustache templates, and no difference in the generated api.

Option should be removed from documentation or re-implemented for typescript-fetch

https://openapi-generator.tech/docs/generators/typescript-fetch

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[macjohnny]

cc @TiFu are the interfaces necessary? classes can also be used as interfaces...

[fuzzzerd]

classes can also be used as interfaces...

Is that the recommended guidance outside the Angular style guide? I've found at least one dissenter: https://www.stevefenton.co.uk/2017/11/typescript-using-classes-interfaces/

are the interfaces necessary?

Even if not, the tooling not providing them when it used to should be a breaking change at least.

[macjohnny]

I agree that a class which contains logic either in the constructor or in some methods should not be used as an interface. However, for generated model-interfaces I think this is not a problem.

Yes, the refactoring caused some breaking changes, this should have been avoided.

[fuzzzerd]

I was not concerned with the models; but with the interfaces for api clients themselves. They used to have interfaces too and are arguably the more valuable piece that was lost.

[Prior99]

We're also kind of stuck with the missing interfaces. We were using them to mock the Apis for testing purposes.