Fix OpenAPI3 converter to generate separate operations for multiple content types

[Copilot]

The OpenAPI3-to-TypeSpec converter was discarding non-multipart content types when multipart was present, generating only one operation instead of multiple operations with @sharedRoute.

Changes

• transform-paths.ts: Split operations with incompatible content types (multipart vs non-multipart) into separate operations with @sharedRoute decorator and content-type-based suffixes
• generate-operation.ts: Removed filtering logic that discarded non-multipart request bodies when multipart was present
• Tests: Added coverage for multiple content type scenarios and updated existing test expecting old behavior

Example

Input OpenAPI operation with multiple content types:

requestBody:
  content:
    multipart/form-data:
      schema: { $ref: '#/components/schemas/FooMultiPart' }
    application/json:
      schema: { $ref: '#/components/schemas/FooJson' }

Now generates two operations instead of one:

@sharedRoute
@route("/my-operation") @post op myOperationMultipart(
  @header contentType: "multipart/form-data",
  @multipartBody body: FooMultiPart,
): Bar;

@sharedRoute
@route("/my-operation") @post op myOperationJson(
  @body body: FooJson
): Bar;

Note: Operations with only non-multipart content types continue to be combined with unions (existing behavior).

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Bug]: [tsp-openapi3] Does not generate parameters for all declared content types.</issue_title>
<issue_description>### Describe the bug

When importing an operation that defines different bodies for different content types, only one is generated in the output.

For example, for this definition:

openapi: 3.1.0
info:
  title: My Spec
paths:
  /my-operation:
    post:
      operationId: myOperation
      requestBody:
        content:
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/FooMultiPart'
          application/json:
            schema:
              $ref: '#/components/schemas/FooJson'
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Bar'

components:
  schemas:
    FooMultiPart:
      type: object
      properties:
        file:
          type: string
          format: binary
        description:
          type: string
      required:
        - file
        - description

    FooJson:
      type: object
      properties:
        name:
          type: string
        age:
          type: integer
      required:
        - name

    Bar:
      type: object
      properties:
        id:
          type: string
        status:
          type: string
      required:
        - id
        - status

It generates:

import "@typespec/http";
import "@typespec/openapi";
import "@typespec/openapi3";

using Http;
using OpenAPI;

@service(#{ title: "My Spec" })
@info(#{})
namespace MySpec;

model FooMultiPart {
  file: HttpPart<bytes>;
  description: HttpPart<string>;
}

model FooJson {
  name: string;
  age?: integer;
}

model Bar {
  id: string;
  status: string;
}

@route("/my-operation") @post op myOperation(
  @header contentType: "multipart/form-data",
  @multipartBody body: FooMultiPart,
): Bar;

Where I would expect (for the operation):

@sharedRoute
@route("/my-operation") @post op myOperationMultipart(
  @header contentType: "multipart/form-data",
  @multipartBody body: FooMultiPart,
): Bar;

@sharedRoute
@route("/my-operation") @post op myOperationJson(
  @header contentType: "application/json",
  @body body: FooJson,
): Bar;

Reproduction

Attached the input used to generate the above example.

repro.zip

Checklist

• Follow our Code of Conduct
• 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.</issue_description>

<agent_instructions>when you are done with the changes, run npx @chronus/chronus add to add a feature changeset. And commit it.</agent_instructions>

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

• Fixes [Bug]: [tsp-openapi3] Does not generate parameters for all declared content types. #8724

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[github-actions]

All changed packages have been documented.

• ✅ @typespec/openapi3

Show changes

@typespec/openapi3 - feature ✏️

[converter] Generate separate operations with @SharedRoute for operations with multiple incompatible content types (e.g., multipart/form-data and application/json)