[Breaking Change] Cross-Version Runtime Exception: Data does not match any schemas from 'oneOf' (AutoRest v2 -> v3)

[mikekistler]

The Breaking Changes check in PR 26672 failed with a runtime exception with "ERROR: Schema violation: Data does not match any schemas from 'oneOf'.

The exception points to an "x-ms-example":

          "NameSpaceCreate": {
            "$ref": "./examples/NameSpaces/EHNamespaceFailover.json"
          }

for an operation with a 202 response that includes an "Azure-AsyncOperation" and a "location" response header. And the example included both of these headers:

  "responses": {
    "202": {
      "headers": {
        "azure-asyncoperation": "http://azure.async.operation/status",
        "location": "eastus"
      }
    }
  }

Through trial and error, I determined that the "location" header was causing the exception, and with a little more experimenting I found that the value had to be a URL. That makes sense, except that the OpenAPI only defined "location" as a "string". Strange!

Anyway, fixing the value of "location" in the example to be a valid URL fixed the runtime exception.

[konrad-jamrozik]

Related investigation:

• [Breaking Change] ERROR: Schema violation: Data does not match any schemas from 'oneOf' #6036

[konrad-jamrozik]

More discussion of oneOf in this Teams thread

Key observation from Timothee Guerin about oneOf being unhelpful error message:

Mentioned earlier but with autorest v3 I migrated to a newer json schema which allows if then which gives a much better error
Like similar to what editor.swagger.io does

[mikekistler]

Another occurrence: https://github.com/Azure/azure-rest-api-specs/pull/27515/checks?check_run_id=20811157978