fix(openapi3): resolve "Duplicate type name" error for named union with bytes in multipart body

[Copilot]

• Analyze root cause of "Duplicate type name" error for multipart union with bytes
• Fix addUsagesInOperation in visibility-usage.ts to traverse multipart body part types
• Add test case for union with bytes in multipart body
• Add changelog entry
• Build and test changes (all 2482 tests pass)
• Apply prettier formatting

Original prompt

---

This section details on the original issue you should resolve

<issue_title>OpenAPI emitter fails on union with bytes for multipart</issue_title>
<issue_description>The following definition

import "@typespec/http";
using Http;

union CreateVideoMultipartBodyInputReference {
  bytes,
  ImageRefParam,
}
union ImageRefParam {
  {
    @maxLength(20971520)
    image_url: url,
  },
  {
    file_id: string,
  },
}
model CreateVideoMultipartBody {

  input_reference?: HttpPart<CreateVideoMultipartBodyInputReference>;
}

op createVideo(
  @header
  contentType: "multipart/form-data",

  @multipartBody
  body: CreateVideoMultipartBody,
): void;

Fails with this error message : Duplicate type name: 'CreateVideoMultipartBodyInputReference'. Check @FriendlyName decorators and overlap with types in TypeSpec or service namespace.

Interestingly, if we replace bytes by string or something else, the emission starts working. I'd expect it to work with bytes as well.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes OpenAPI emitter fails on union with bytes for multipart #10045

---

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[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/openapi3@10046

commit: 7019add

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension

[baywet]

@copilot run the formatting command, commit the changed files, do nothing else

[Copilot]

@copilot run the formatting command, commit the changed files, do nothing else

Done in 7019add.

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