[Bug]: behavior change to HttpOperationResponse.response.body.type in 0.56.0-dev

[weidongxu-microsoft]

Describe the bug

HttpOperationResponse.responses.body.type changes in 0.56.0-dev, compared to 0.55.0

case in cadl-ranch
https://github.com/Azure/cadl-ranch/blob/main/packages/cadl-ranch-specs/http/type/model/visibility/main.tsp#L50-L51

in 0.55.0, the response.body.type is VisibilityModel model with 5 properties

in next, it is an anonymous model with only 1 property (the one with "read")

---

There is some other cases of difference in response, e.g. empty model
https://github.com/Azure/cadl-ranch/blob/main/packages/cadl-ranch-specs/http/type/model/empty/main.tsp#L35

Also see some diff of response status code changed from 204 to 200.

Reproduction

https://github.com/Azure/cadl-ranch/blob/main/packages/cadl-ranch-specs/http/type/model/visibility/main.tsp#L50-L51

next

{
  '@typespec/compiler': '0.56.0-dev.18',
  '@typespec/http': '0.56.0-dev.10',
  '@typespec/openapi': '0.56.0-dev.3',
  '@typespec/rest': '0.56.0-dev.4',
  '@typespec/versioning': '0.56.0-dev.3',
  '@azure-tools/typespec-client-generator-core': '0.42.0-dev.10',
  '@azure-tools/typespec-azure-core': '0.42.0-dev.5',
  '@azure-tools/typespec-azure-resource-manager': '0.42.0-dev.11',
  '@typespec/eslint-config-typespec': '0.56.0-dev.1',
  '@typespec/library-linter': '0.56.0-dev.3'
}

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• The provided reproduction is a minimal reproducible example of the bug.

[weidongxu-microsoft]

Found in nightly build, e.g.
https://dev.azure.com/azure-sdk/internal/_build/results?buildId=3708464&view=logs&j=ca395085-040a-526b-2ce8-bdc85f692774&t=8d0a7aee-8090-5653-72a7-7c81ab87cde7&l=12985

[weidongxu-microsoft]

Chenjie notified me that it may be caused by PR #2945

Would e.g. op getModel(@body input: VisibilityModel): @body VisibilityModel; able to make the case follow the behavior of 0.55 ?
(SDK would at least need to know how to make service write an exact round-trip model, e.g. a SDK API from a PUT REST API should take a Resource in request body and return a Resource in response body, even if there is some difference of e.g. @visibility on a few properties -- which would be handled within the model class, e.g. no setter if readOnly, no getter if no "read")

[timotheeguerin]

This has been done by design to make sure request and response body resolution use the exact same logic. Http library was doing some very inconsitent thing that were completely blocking and breaking certain scenarios. The change it that the body property is not exactly the body in both the request and response instead of just being in the request and in the response sometimes being the wrapper model.

Use the same logic you did for request and it will work fine.

[weidongxu-microsoft]

Thanks Timothee.

I will go update the cadl-ranch to e.g.

@get
op getModel(@body input: VisibilityModel): {
  @body output: VisibilityModel
};

Azure/cadl-ranch#567

However, I may reopen it, if we see behavior changed on real service.