[Bug]: encoded-name-conflict when using @visibility, @encodedName and a visibility transform together

[edouardhue]

Describe the bug

When using both decorators @visibility and @encodedName on a property of a model, and using the model in an operation with an explicit visibilty transform, an error occurs: "encoded-name-conflict Same encoded name 'some_name' is used for 2 members 'application/json'".

The issue does not occur when using @typespec/http's automatic visibility inclusion: the proper property is included and its name is properly encoded. The operation has to use a Transform such as Read<T> for the issue to come up.

Using explicit visibility transforms is not discouraged in the documentation, but no example is provided of them combined with encoded names. Is this a known limitation? Are there any workarounds?

Reproduction

Playground Link

Checklist

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• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.

[witemple-msft]

This is definitely a bug and not a known limitation of the explicit transforms. I'm not exactly sure why this is happening, and I think it's some kind of issue with our validator that tracks duplicate names here. Logically, there should be no reason for this duplicate property metadata to occur like this, but we appear to have found a way.

[witemple-msft]

Possibly related: #7837

[witemple-msft]

Confirming that the above referenced playground link compiles successfully and generates the expected schemas in #8681.