[BUG] [DART][DART-DIO] API calls using parameters that take Lists are not being made correctly

Bug Report Checklist

• [✔ ] Have you provided a full/minimal spec to reproduce the issue?
• [ ✔] Have you validated the input using an OpenAPI validator (example)?
• [✔ ] What’s the version of OpenAPI Generator used? 4.3.1
• [ ✔] Have you search for related issues/PRs? Yes, without fruition
• [✔ ] What’s the actual output vs expected output?

Description

I’ve got an API generated using the dart-dio class that has an API call where some of the parameters take lists of strings. On those parameters the API call seems to insert [] (or the HTTP character encoding equivalent) before the = of the api request. e.g. http://komga.my.domain/api/v1/books?read_status[]=IN_PROGRESS when it should look like: https://komga.my.domain/api/v1/books?read_status=IN_PROGRESS

If you pass more than one item in the list, e.g. bookApi.getAllBooks(readStatus: ["IN_PROGRESS","READ"]) then the API request looks like this:

http://komga.my.domain/api/v1/books?read_status%5B%5D=IN_PROGRESS&read_status%5B%5D=READ when it should look like this: https://komga.my.domain/api/v1/books?read_status=READ&read_status=IN_PROGRESS

openapi-generator version

latest stable - 4.3.1

OpenAPI declaration file content or url

https://demo.komga.org/v3/api-docs/REST API

Command line used for generation

java -jar .\openapi-generator-cli.jar generate -i '.\REST API.json' -g dart-dio --additional-properties=dateLibrary=timemachine -o .\komga_api_client\ -c .\config.yaml

(the config.yaml merely contains some purely aesthetic parameters around branding)

I have a copy of the generated code in a github repo here - https://github.com/frameset/komga_api_client

Steps to reproduce

You could clone my github repo https://github.com/frameset/komga_client into an android studio project, open the screens\serverhome.dart page and modify line 101 to read: future: bookApi.getAllBooks(readStatus: ["IN_PROGRESS"]), Then start the app in an emulator and enter the server details Server: demo.komga.org Username: [e-mail] Password: komga-demo

You may need to capture the http traffic in some way as dart devtools does not have this facility yet.

Related issues/PRs

I could not find something that closely matches the problem.

Suggest a fix

I am unsure personally, as this is beyond my understanding.

[kuhnroyal]

There is a partial solution for this available in dio 4.0.0 but that requires breaking changes in the generator.

[kuhnroyal]

I am really interested in getting this fixed but Dio seems inactive atm. We could provide a custom DioPatched and RequestOptionsPatched class that does this correctly.