SingleRequestParameter setter parameter construction

[Mattias-Sehlstedt]

fix #20668

Introduces so that the argument class which is generated for useSingleRequestParameter can be constructed similar to the POJO models. The implementation uses the new (but yet to be released) "static" setting to further expand on the behavior of useSingleRequestParameter.

I have realize this behavior with mustache configuration rather than lombok to make it easier to make the behavior even more similar to that of POJOs in the future (e.g., sort parameters so required ones are highlighed in some sense, adding nullable annotations to class fields to highlight/trigger runtime errors when they are required). A single lombok annotation is used to provide equals to the class, to facilitate easier testing when working with mocks and verifying them. I will investigate how to add an equals implementation as a separate issue.

The current implementation for useSingleRequestParameter uses a record for RestClient, and a class for WebClient. In order to bring these SpringClients closer to each other, I have made it so that the RestClient will switch to also using a class when "static" is provided (but retain a record for "true" as to not make a breaking change).

A better description than ..., but also makes the generated arguments class static with single parameter instantiation can probably be made.

cc @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08)

Edit notes: clarified that I will omit the equals implementation and instead do it separately so I can have time to investigate how to properly express it with mustache syntax.

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[wing328]

thanks for the PR

also cc @cchacin

[wing328]

@Mattias-Sehlstedt can you please review the CI failure when you've time?

[Mattias-Sehlstedt]

Just copying the pojo implementation obviously doesn't get the job done properly. Will investigate if I am able to adjust it or if I will drop equals/hashcode entirely.

I assume the change is to replace Vars with Params in the mustache. But I am not sure what extension settings that would be relevant.

[cchacin]

LGTM 👍

[martin-mfg]

With both webclient and restclient, when using the new option useSingleRequestParameter=static the generated code doesn't compile. Please fix.