openapi-generator: [JAVA] Untyped request bodies not handled

Description

Generating code (both client and server) for a model where a resource has a body parameter with either no type or of type object generates a warning and code which does not compile.

Warning this generates is similar to:

[main] WARN  o.o.codegen.DefaultCodegen - Unknown type found in the schema: object
[main] WARN  o.o.codegen.DefaultCodegen - The following schema has undefined (null) baseType. It could be due to form parameter defined in OpenAPI v2 spec with incorrect consumes. A correct 'consumes' for form parameters should be 'application/x-www-form-urlencoded' or 'multipart/form-data'
[main] WARN  o.o.codegen.DefaultCodegen - schema: class ObjectSchema {
    class Schema {
        title: null
        multipleOf: null
        maximum: null
        exclusiveMaximum: null
        minimum: null
        exclusiveMinimum: null
        maxLength: null
        minLength: null
        pattern: null
        maxItems: null
        minItems: null
        uniqueItems: null
        maxProperties: null
        minProperties: null
        required: null
        type: null
        not: null
        properties: null
        additionalProperties: null
        description: null
        format: null
        $ref: null
        nullable: null
        readOnly: null
        writeOnly: null
        example: null
        externalDocs: null
        deprecated: null
        discriminator: null
        xml: null
    }
    type: object
    defaultObject: null
}
[main] WARN  o.o.codegen.DefaultCodegen - codegenModel is null. Default to UNKNOWN_BASE_TYPE

Generated client code in DefaultApi:

import org.openapitools.client.model.UNKNOWN_BASE_TYPE;

...

public void thePost(UNKNOWN_BASE_TYPE UNKNOWN_BASE_TYPE) throws ApiException {

    thePostWithHttpInfo(UNKNOWN_BASE_TYPE);
}

No such model is generated though even if it was, it wouldn’t be terribly useful. The server generated code has a very similar problem.

I have tried this with both type: object and no type specified.

openapi-generator version

I’ve tried with 3.3.2 and master.

OpenAPI declaration file content or url

{
  "swagger": "2.0",
  "info": {
    "version": "0.0.1",
    "title": "Test"
  },
  "basePath": "/",
  "paths": {
    "/": {
      "post": {
        "operationId": "thePost",
        "parameters": [
          {
            "in": "body",
            "name": "body",
            "required": "false",
            "schema": {
                "type": "object"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "response"
          }
        }
      }
    }
  }
}

Command line used for generation

Client generation: java -jar ~/.m2/repository/org/openapitools/openapi-generator-cli/3.3.2/openapi-generator-cli-3.3.2.jar generate -c config.json -i api.json -g java -o output

The contents of config.json are:

{
  "library": "jersey2"
}

Having said that, I have tried with other libraries and the same problem exists.

Server generation: java -jar ~/.m2/repository/org/openapitools/openapi-generator-cli/3.3.2/openapi-generator-cli-3.3.2.jar generate -i api.json -g jaxrs-jersey -o output

Steps to reproduce

Generate code with the model above and compile.

Related issues/PRs

This looks similar to https://github.com/OpenAPITools/openapi-generator/pull/1078 but the proposed fix in that PR doesn’t resolve this particular problem.

Suggest a fix/enhancement

I have been able to fix this by changing https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java#L4556 to set codegenModelName to typeMapping.get("Object") instead of the hardcoded UNKNOWN_BASE_TYPE. I’m not totally convinced that’s the right fix though but if it is I’m happy to open a PR with that.