[BUG] [Kotlin-Client] Strange DefaultApi import when mapping custom types

[sivieri]

Description

When generating a Kotlin client with an API that uses custom types, I would prefer to use my own data classes instead of the ones generated by OpenAPI.
However, when specifying these classes in the configuration, the import clauses in DefaultApi are wrong, and I am not sure if my configuration is wrong or if there is a problem in OpenApi.

I have tried different combinations of adding or omitting the full package in the configuration both for typeMapping and for importMapping, and the results are varied (e.g., a configuration adds the wrong import, another creates the data class even with the mapping specified, another collapses the package and class name removing the dots...).

Let me know if there is a correct combination of typeMapping and importMapping that eludes me, to obtain the expected result, or if there is a problem with OpenApi.

openapi-generator version

The problem was found with version 4.2.0, and it remains if using master.

OpenAPI declaration

openapi: 3.0.1
paths:
  /operations/{operationId}:
    get:
      summary: Retrieve the descriptor of an operation.
      operationId: getOperation
      parameters:
      - name: operationId
        in: path
        description: Id of the operation.
        required: true
        schema:
          type: integer
          format: int32
        example: 1
      responses:
        200:
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CustomType'
        404:
          description: Operation not found
components:
  schemas:
    CustomType:
      type: object
      properties:
        name:
          type: string
          format: uuid

Configuration

{
  "packageName": "some.package",
  "groupId": "mygroup",
  "artifactId": "myclient",
  "artifactVersion": "1.0",
  "enumPropertyNaming": "UPPERCASE",
  "serializationLibrary": "gson",
  "serializableModel": "true",
  "dateLibrary": "java8",
  "collectionType": "list",
  "library": "jvm-okhttp3",
  "typeMappings": {
    "CustomType": "CustomType"
  },
  "importMappings": {
    "CustomType": "some.other.package.CustomType"
  }
}

Command line used for generation

java -jar openapi-generator-cli.jar generate -g kotlin -o xxx -i sample-api.yaml -c sample-config.json --skip-validate-spec

Expected behavior

Import declaration:
import some.other.package.CustomType
Method signature:
fun getOperation(operationId: kotlin.Int) : CustomType

Actual behavior

Import declaration:
import some.package.models.some.other.package.CustomType
Method signature:
fun getOperation(operationId: kotlin.Int) : some.other.package.CustomType

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[wldmr]

I stumbled over this bug today. As a workaround, I used the Maven replacer Plugin to simply remove the offending import:

<plugin>
    <groupId>com.google.code.maven-replacer-plugin</groupId>
    <artifactId>replacer</artifactId>
    <version>${replacer.version}</version>
    <executions>
        <execution>
            <!-- This is a workaround for https://github.com/OpenAPITools/openapi-generator/issues/4420
            OpenApi-Generator creates wrong imports when using the `importMapping` parameter:
            It concatenates the model package and the qualified name of the import mapping.
            Since the import mapping contains the qualified name already and is used throughout the file,
            we can simply remove the complete erroneous import line.
             -->
            <phase>generate-sources</phase>
            <goals>
                <goal>replace</goal>
            </goals>
            <configuration>
                <basedir>${project.build.directory}</basedir>
                <includes>
                    <include>generated-sources/openapi/src/main/**/*.kt</include>
                </includes>
                <regex>true</regex>
                <token>import ${openapi-generator-maven-plugin.modelPackage}.some.other.package.+\n</token>
            </configuration>
        </execution>
    </executions>
</plugin>

Note that I only used importMappings and no typeMappings, as importMappings seems to replace all usages of the OpenApi types with the one from the mappings (which seems kind of wrong to me also, but it works in my favor here).