[BUG][Kotlin][Multiplatform] Request under incorrect path made if query object parameter used

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Please read "OpenAPI declaration file content or url" section first. This paragraph uses API defined there.

If there's a query parameter that is not a simple type, but an object:

 - name: someComplexQueryParameter
   in: query
   required: true
   schema:
     "$ref": "#/components/schemas/SomeObject"

the generated code is invalid - it calls toString() on the object which fires the auto-generated toString() in the data class:

val localVariableQuery = mutableMapOf<String, List<String>>()
someComplexQueryParameter?.apply { localVariableQuery["someComplexQueryParameter"] = listOf("$someComplexQueryParameter") }

Compare paths under which the request is made (I presume):

Expected:
https://some-service.com/somePath?someProperty=someValue

Actual:
https://some-service.com/somePath?someComplexQueryParameter=SomeObject(someProperty=someValue)

openapi-generator version

5.2.1. I don't know if it's a regression, I never saw it working.

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: Test API
  version: '1'
paths:
  "/somePath":
    get:
      operationId: someOperation
      parameters:
      - name: someComplexQueryParameter
        in: query
        required: true
        schema:
          "$ref": "#/components/schemas/SomeObject"
      responses:
        '200':
          description: OK
components:
  schemas:
    SomeObject:
      type: object
      properties:
        someProperty:
          type: string

Generation Details

Using the Gradle plugin:

openApiGenerate {
    generatorName.set("kotlin")
    library.set("multiplatform")
}

Steps to reproduce

Just generate the code using the settings given above.

Related issues/PRs

I haven't found one.

Suggest a fix

I worked around the issue by changing the generated code from:

val localVariableQuery = mutableMapOf<String, List<String>>()
someComplexQueryParameter?.apply { localVariableQuery["someComplexQueryParameter"] = listOf("$someComplexQueryParameter") }

to

val localVariableQuery = mutableMapOf<String, List<String>>()
with(someComplexQueryParameter) {
    someProperty?.let { localVariableQuery["someProperty"] = listOf("$query") }
}

but I don't know how it should be adjusted for other types of properties, and didn't think about edge cases.

Run the Gradle openApiGenerate configuration with generatorName kotlin and library multiplatform against the supplied OpenAPI spec. Inspect the generated request query construction and compare it with the expected someProperty query; done means the request no longer serializes the object as SomeObject(someProperty=someValue).