Core: Validation throws error when using fastapi.sse

[BHznJNs]

Description

I am trying to use the new SSE function in the latest version of FastAPI, the fastapi.sse will attach itemSchema field in the generated openapi endpoint definition like this:

{
  "openapi": "3.1.0",
  "info": {
    "title": "FastAPI",
    "version": "0.1.0"
  },
  "paths": {
    "/api/events/": {
      "post": {
        "tags": [
          "stream"
        ],
        "summary": "Sse Endpoint",
        "operationId": "sse_endpoint",
        "responses": {
          "200": {
            "description": "Successful Response",
            "content": {
              "text/event-stream": {
                "itemSchema": {
                  "type": "object",
                  "properties": {
                    "data": {
                      "type": "string"
                    },
                    "event": {
                      "type": "string"
                    },
                    "id": {
                      "type": "string"
                    },
                    "retry": {
                      "type": "integer",
                      "minimum": 0
                    }
                  }
                }
              }
            }
          },
          "400": {
            "description": "Bad Request",
            "content": {
              "text/event-stream": {
                "schema": {
                  "$ref": "#/components/schemas/ErrorResponseSchema"
                }
              }
            }
          },
          "401": {
...

And when the itemSchema appear, the orval will throw an error like this:

api - Validation failed
Cause: [
{
  "message": "if must match \"else\" schema",
  "path": "/paths/~1api~1events~1"
},                                                    
...                                                     

And I have to manually exclude the sse endpoints in the fastapi app to make orval normally generate other schemas. I have already excluded sse endpoints in the orval config.

Configuration (orval.config)

import { defineConfig, type InputOptions, type OperationOptions } from "orval";

const operationSpecificConfig: Record<string, OperationOptions> = {
  fetch_models: {
    query: {
      useInfinite: false,
      useSuspenseInfiniteQuery: false,
    },
  },
};

const input: InputOptions = {
  target: "../openapi.json",
  filters: {
    mode: "exclude",
    tags: ["stream"],
  },
};

export default defineConfig({
  api: {
    input,
    output: {
      clean: true,
      target: "./src/api/generated/endpoints/",
      schemas: "./src/api/generated/schemas/",
      operationSchemas: "./src/api/generated/schemas/params/",
      client: "react-query",
      mode: "tags-split",
      namingConvention: "kebab-case",
      override: {
        useTypeOverInterfaces: true,
        fetch: {
          includeHttpResponseReturnType: false,
        },
        mutator: {
          path: "./src/api/orval-mutator/custom-fetch.ts",
          name: "fetchApi",
        },
        query: {
          version: 5,
          useQuery: true,
          useInfinite: true,
          useMutation: true,
          useSuspenseQuery: true,
          useSuspenseInfiniteQuery: true,
          useInfiniteQueryParam: "page",
        },

        operations: operationSpecificConfig,
      },
    },
    hooks: {
      afterAllFilesWrite: ["biome format --write --config-path config/biome.format.jsonc"],
    },
  },
});

Environment

System:
OS: Windows 11 10.0.26200
CPU: (16) x64 AMD Ryzen 7 6800HS Creator Edition
Memory: 2.15 GB / 13.69 GB

Expected behavior

Orval just ignore the sse endpoints and normally resolve others.

Actual behavior

Orval immediately throws error and exit.

OpenAPI document (minimal, if applicable)

{
  "openapi": "3.1.0",
  "info": {
    "title": "FastAPI",
    "version": "0.1.0"
  },
  "paths": {
    "/api/events/": {
      "post": {
        "tags": [
          "stream"
        ],
        "summary": "Sse Endpoint",
        "operationId": "sse_endpoint",
        "responses": {
          "200": {
            "description": "Successful Response",
            "content": {
              "text/event-stream": {
                "itemSchema": {
                  "type": "object",
                  "properties": {
                    "data": {
                      "type": "string"
                    },
                    "event": {
                      "type": "string"
                    },
                    "id": {
                      "type": "string"
                    },
                    "retry": {
                      "type": "integer",
                      "minimum": 0
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Additional context

No response