Add custom mapper for snake case to camel case

[akreit]

Checklist

• I read the documentation at https://chimney.readthedocs.io/ and checked that the functionality doesn't exist
• I checked the https://github.com/scalalandio/chimney/issues and haven't found the feature already requested reported
• I confirmed that the request is not related to functionality that was deprecated: lifted transformers (TransformerFs) or unsafeOption flags
• I believe that this is actual feature request, rather than a question how to use existing features
• I am aware of the maintainer's announcement and I understand, that this might only be implemented
  if someone from the community decide to own the feature and see it through

Describe the desired behavior

I came across a case where I wanted to transform case class objects with camelCase member names into case class objects with snake case member names.
After researching a bit I came across this discussion and the related PR: #89

The related PR pointed me to the docs: https://chimney.readthedocs.io/en/stable/supported-transformations/#defining-custom-name-matching-predicate

With that, I implemented a mapper which works well enough:

case object CamelSnakeCaseEquality extends TransformedNamesComparison {
  def namesMatch(fromName: String, toName: String): Boolean = {
    val snakeCase = fromName
      .flatMap { c =>
        if (c.isUpper) Seq('_', c.toLower)
        else Seq(c)
      }
      .mkString
    snakeCase == toName
  }
}

Unless any of the existing extensions of TransformedNamesComparison already provide this functionality (which I could not find), I imagine this to be a common enough case to come with chimney out of the box.

Any opinions on this?

PS: I'd be happy to raise a PR for this.

Use case example

case class UserDAO(userId, createdAt)
case class UserDTO(user_id, created_at)

UserDAO(123, "2024-12-03T12:00:00")
   .into[UserDTO]
   .enableCustomFieldNameComparison(
        CamelSnakeCaseEquality
   )
   .transform

How it relates to existing features

Yes, as stated above, this can be (self) implemented using existing functionality.

Additional context

Add any other context about the problem here.

[MateuszKubuszok]

Hey @akreit, thanks for taking your time to write this!

It makes sense, I've heard from other people that it could be useful.

If you are interested in making PR, I am all for it. It would just have to add a test here and mention it in the docs.