[BUG][typescript-fetch] Name convention of generated request type is different from spec file.

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?
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Description

When I generated typescript-fetch client with YAML file and command below, the code below will be generated.

/* tslint:disable */
/* eslint-disable */
/**
 * ts-snake-case-params
 * ts-snake-case-params
 *
 * The version of the OpenAPI document: 0.0.1
 * 
 *
 * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
 * https://openapi-generator.tech
 * Do not edit the class manually.
 */


import * as runtime from '../runtime';

export interface TestGetRequest {
    pageNum?: number;
}

/**
 * 
 */
export class DefaultApi extends runtime.BaseAPI {

    /**
     * description
     * summary
     */
    async testGetRaw(requestParameters: TestGetRequest): Promise<runtime.ApiResponse<void>> {
        const queryParameters: runtime.HTTPQuery = {};

        if (requestParameters.pageNum !== undefined) {
            queryParameters['page_num'] = requestParameters.pageNum;
        }

        const headerParameters: runtime.HTTPHeaders = {};

        const response = await this.request({
            path: `/test`,
            method: 'GET',
            headers: headerParameters,
            query: queryParameters,
        });

        return new runtime.VoidApiResponse(response);
    }

    /**
     * description
     * summary
     */
    async testGet(requestParameters: TestGetRequest): Promise<void> {
        await this.testGetRaw(requestParameters);
    }

}

As you can see, request parameter on spec file is like this.

paths:
  /test:
    get:
      summary: summary
      description: description
      operationId: testGet
      parameters:
        - name: page_num
          in: query
          schema:
            type: number
      responses:
        '200':
          description: OK

One of request parameter page_num is snake case.
But request parameter on generated code is camel case.

export interface TestGetRequest {
    pageNum?: number;
}

I tried most of option to make name convention of generated code as same as YAML file, but finally I couldn't find such an option...
In my opinion, even if default behavior is like this, there should be option to specify name convention for request parameter.
Because web frontend engineer will see API spec generated from YAML file, but generated client's parameter is different from spec.
It'll be a little bit confusing.

openapi-generator version

v4.3.1 (via Docker image)

OpenAPI declaration file content or url

You can see here

Generation Details

The command I executed is below(Docker command is omitted to simplify command).
Without any config file.

generate -g typescript-fetch \
		-pnpmName='${TAG_NAME}' \
		-psupportsES6=true \
		-ptypescriptThreePlus=true \
		-i /local/spec.yml \
		-o /local/dist

Steps to reproduce

1. Write YAML file and add query request parameter with snake case
2. Generate client

that's all

Related issues/PRs

I can't find any related / similar issue.

Suggest a fix

If we want to avoid breaking changes, adding new option to specify naming convention for request parameter is the best way I think.

Start with the linked sandbox spec.yml and reproduce the typescript-fetch generation using the command shown in the issue. Compare the snake_case page_num in the specification with the generated TestGetRequest interface, then trace the naming behavior and determine how an option could preserve the specified parameter name without changing existing defaults.