Nesting a multiple field validation loses the error about elm-form HOT 2 CLOSED

Hello,
Finally found the time to look at your issue, it's effectively a grouping problem.

In there:

thingCombinationValidation : Validation MyError ( Thing, Thing )
thingCombinationValidation =
    field "firstThing" thingValidation
        |> andThen
            (\fst ->
                field "secondThing" thingValidation
                    |> andThen
                        (\snd ->
                            if List.member ( fst, snd ) forbiddenCombinations then
                                fail (customError InvalidCombination)
                            else
                                succeed ( fst, snd )
                        )
            )

The fail (customError InvalidCombination) isn't attached to a field, like that, so error is lost in errors tree, see how it's done in lib:
https://github.com/etaque/elm-form/blob/master/src/Form/Validate.elm#L131

So what you can do is to use field to attach your custom error, like so:

field "firstThing" (fail (customError InvalidCombination))

Maybe that kind of error could be caught by better types. Worth investigating!

from elm-form.

Thank you for looking into this! I was pretty sure I had answered during the holidays, but just noticed I hadn't. Sorry about that!

Using field to add an error works, but is not really intuitive. Maybe adding a function like failAtField implemented in terms of field and fail as shown above would make it clearer.

from elm-form.