[BUG] [Java] 7.1.0 generates broken APIs for models consisting only of additionalProperties

[bonii-xx]

Description

Updating the openapi-generator-maven-plugin to 7.1.0 breaks all APIs which use models consisting only of additionalProperties. It looks like model generation is skipped for those models, however the API still uses them, and they're also beneficial for the code in general since they serve as an anti-corruption layer.

openapi-generator version

7.1.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: bug
  version: 1.0.0

paths:
  /test:
    post:
      responses:
        default:
          description: dummy response
          content:
            application/json:
              schema:
                type: object
      requestBody:
        description: additional properties only
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/TestRequestBody'
      operationId: getQuestionnaire

components:
  schemas:
    TestRequestBody:
      type: object
      description: A schema consisting only of additional properties
      additionalProperties: true

Generation Details

            <!-- OpenAPI code generators -->
            <plugin>
                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>7.1.0</version>
                <executions>
                    <execution>
                        <id>test</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>${project.basedir}/src/main/resources/openapi/openapi-bug.yaml</inputSpec>
                            <generatorName>spring</generatorName>
                            <configOptions>
                                <library>spring-boot</library>
                                <interfaceOnly>true</interfaceOnly>
                                <serializableModel>true</serializableModel>
                                <useSpringBoot3>true</useSpringBoot3>
                            </configOptions>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

Steps to reproduce

Generate the provided api-specification using the provided configuration.

The generator logs:

[INFO] Model TestRequestBody not generated since it's a free-form object

while the generated DefaultApi.java class uses:

default ResponseEntity<Object> getQuestionnaire(
        @Parameter(name = "TestRequestBody", description = "additional properties only") @Valid @RequestBody(required = false) TestRequestBody testRequestBody
    ) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);

    }

which doesn't compile, since the TestRequestBody class wasn't generated.

Related issues/PRs

Suggest a fix

Don't skip generation of free-form objects. There's a reason why the api-specification uses a separate schema with title to define the model, instead of using an inline object.

[ignacioel]

Hi,
I facing same issue after updating to 7.1.0.
I think I have tracked the specific change to this PR: #16613

[martin-mfg]

Hi @ignacioel, thanks for taking the time to track down the relevant commit for this issue.