Introduce other common Validator

[geirolz]

What do you think to add some new generic Validator? I have in mind these for now:

  //foldable - from cats
  def nonEmpty[F[_]: Foldable, T]: Validator[F[T]]
  def fixedSize[F[_]: Foldable, T](n: Int): Validator[F[T]]

  //strings
  def nonEmptyString[T <: String]: Validator[T]
  def fixedLength[T <: String](n: Int): Validator[T]

  //numbers
  def positive[N](implicit N: Numeric[N]): Validator[N]
  def negative[N](implicit N: Numeric[N]): Validator[N]
  def inRange[N: Numeric](min: N, max: N, minExclusive: Boolean = false, maxExclusive: Boolean = false): Validator[N]

Reasons:

• Avoid boilerplates / duplicated code across microservices
• Standardize messages

Foldable

With Foldable instead of Iterable we can also support cats collections like NonEmptyList, etc... If we don't want to use Cats obliviously we can use Iterable but then creating the same validators with Foldable in the cats module.

[adamw]

Why not :) Some of these for sure would make sense. Thanks for the idea!

We can't depend on cats in core so this would have to be split among the two modules as you've written.

[geirolz]

Great if you want I can work on it, I've already have something done in my app.

Just one question, using custom validators there won't be any message on the open API doc. there is a way to customize it?

[adamw]

Sure, contributions welcome! :)

As for messages, you can return custom validation error messages when using Validator.Custom. Here, though, we'll probably end up with customised primitive validators which would need to return custom messages ... that's not possible currently, but if you do have some design propositions, go ahead :) All the code is in Validator

[geirolz]

As "message on the open API doc" I was meaning something like minimum=0 when we set a Min(0) validator for example. OpenAPI can have custom messages there ?

[adamw]

@geirolz yeah, this should work now. Are you not seeing this when using validators? Here's the section that generates these messages: https://github.com/softwaremill/tapir/blob/master/core/src/main/scala/sttp/tapir/server/interceptor/decodefailure/DecodeFailureHandler.scala#L176-L199

[geirolz]

@adamw these are the messages in case of error right? I was meaning the information message in the Open API documentation HTML page, there is a way to customize them?

Anyway, what do you think to take the validator and the message for the error case closer?

I'll open a draft PR in the next days for a design proposal. I still have some problems but in this way we can discuss the design

[adamw]

Ah ... I think these messages are generated by the ui, in the openapi docs you only have the metadata, e.g. minimum: 0, without any error messages. So if there's a way to customise them, it's probably in Swagger? See https://swagger.io/specification/#schema-object

[adamw]

The code generating this in tapir is in TSchemaToASchema

[geirolz]

@adamw here just a draft https://github.com/geirolz/tapir/tree/refactoring-validator

Core is fine, there are some modules with red tests to fix, I'll if you are interested in this design.

[adamw]

@geirolz I see you've got a bigger refactor there :) The direction looks good, maybe you can open a PR so that I could comment on individual parts? Should be easier this way

[geirolz]

For sure! Sorry I was in a hurry yesterday

Here is the draft PR: https://github.com/softwaremill/tapir/pull/1467