[Bug]: Anonymous unions in models referenced in union/@event decorator don't get generated name

[MaiLinhP]

Describe the bug

When upgrading OpenAI repo to new TCGC version, we're getting an issue where the same anonymous unions in different models are not getting generated names but collapse into an unnamed type, causing duplicate client name error. These seem to happen to unions in models referenced in other unions/@event decorator

Reproduction

Example 1
Example 2

Checklist

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

[MaiLinhP]

@tadelesh I'm new to this area and just want to check with you that this is indeed a bug and not normal behavior? We do have a workaround if this behavior is expected :)

[tadelesh]

@MaiLinhP When the HTTP response is a union, the core HTTP lib gives TCGC separated response instead of a union type. (@timotheeguerin It should be intentional for HTTP lib, right? Here the response is a named union, but be split into different response type. It seems inconsistent when we add @body for this union) Then TCGC will create a synthetic union to compose them. There is a bug in current logic that: 1. does not give name for such case 2. create union of union for such case. To address this, or say if you want to use service specific name (e.g., StreamingResponse), you could change the spec with @body wrapper: op createStream(): {@body body: StreamingResponse};.