[BUG] Body argument is treated as plain map rather than object when `additionalProperties` is `true`

When generating an API client for and endpoint whose requestBody's schema allows additional properties the arguments of an API call function drop to a plain map rather than a typed structure, e.g.:

typescript-axios

//...
    public relaxedPost(requestBody: { [key: string]: object; }, options?: AxiosRequestConfig) {
        return DefaultApiFp(this.configuration).relaxedPost(requestBody, options).then((request) => request(this.axios, this.basePath));
//...
    public strictPost(strict: Strict, options?: AxiosRequestConfig) {
        return DefaultApiFp(this.configuration).strictPost(strict, options).then((request) => request(this.axios, this.basePath));
    }
}

java:

//...
    public okhttp3.Call relaxedPostCall(Map<String, Object> requestBody, final ApiCallback _callback) throws ApiException {
//...
    public okhttp3.Call strictPostCall(Strict strict, final ApiCallback _callback) throws ApiException {

I want in both cases the body argument to be typed according to relevant type definition Relaxed and Strict like this:

typescript-axios

//...
    public relaxedPost(relaxed: Relaxed, options?: AxiosRequestConfig) {
        return DefaultApiFp(this.configuration).relaxedPost(requestBody, options).then((request) => request(this.axios, this.basePath));
//...
    public strictPost(strict: Strict, options?: AxiosRequestConfig) {
        return DefaultApiFp(this.configuration).strictPost(strict, options).then((request) => request(this.axios, this.basePath));
    }
}

java:

//...
    public okhttp3.Call relaxedPostCall(Relaxed relaxed, final ApiCallback _callback) throws ApiException {
//...
    public okhttp3.Call strictPostCall(Strict strict, final ApiCallback _callback) throws ApiException {

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

openapi-generator version

openapi-generator-cli 5.3.1-SNAPSHOT
  commit : eeb00e2
  built  : 2021-11-20T01:56:03Z
  source : https://github.com/openapitools/openapi-generator
  docs   : https://openapi-generator.tech/

OpenAPI declaration file content or url

openapi: '3.0.2'
info:
  title: API Title
  version: '1.0'
servers:
  - url: https://api.server.test/v1
paths:
  /strict:
    post:
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Strict'
      responses:
        '200':
          description: OK

  /relaxed:
    post:
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Relaxed'
      responses:
        '200':
          description: OK



components:
  schemas:
    Strict:
      title: Strict
      additionalProperties: false
      properties:
        id:
          type: string
        name:
          type: string
      required:
        - id
        - name
    Relaxed:
      title: Relaxed
      additionalProperties: true
      properties:
        id:
          type: string
        name:
          type: string
      required:
        - id
        - name

Generation Details

Create a script: generate.sh

#!/usr/bin/env bash

INPUT=$1
LANGUAGE=$2

OUTPUT_DIR="open-api-generator/$INPUT/$LANGUAGE"

mkdir -p $OUTPUT_DIR

set -x

docker run --rm \
    -v $PWD:/local openapitools/openapi-generator-cli generate \
    -i "local/$INPUT" \
    -g $LANGUAGE \
    -o "/local/$OUTPUT_DIR"

Steps to reproduce

Run it as:

./generate.sh bug.yaml typescript-axios
./generate.sh bug.yaml java

Related issues/PRs

Suggest a fix

Start with the OpenAPI declaration and generate.sh reproduction using the typescript-axios and java generators. Compare the generated relaxedPost and strictPost signatures with the expected Relaxed and Strict types. Done means request bodies with additionalProperties: true retain their named schema types in both generated clients.