Better arguments and inputs validation

[gustavovnicius]

It would be good to have something similar to how grape validates and coerce parameters: https://github.com/ruby-grape/grape#parameter-validation-and-coercion
Things like: mutually_exclusive, exactly_one_of, and custom validators

[rmosolgo]

Thanks for the suggestion! Best of all would be to implement these via query analyzers, so you can run validation before starting to execute the query.

[modosc]

@rmosolgo do you have an example of accessing parameters inside of a QueryAnalyzer? i can find the giant params object but i can't figure out how to go from a given irep_node to the supplied value.

[modosc]

sorry - i should be more specific. i see how to get access to the single arguments object passed in but i don't want to parse that tree again since it's already been done once in static validation. would it be possible to get the irep_node in the static validation proc?

[rmosolgo]

No, it's not possible to get the irep_node during validation, because it hasn't been built yet! InternalRepresentation::Rewrite actually tags along behind the validation visitors, building irep_nodes as validation finishes.

[modosc]

hah, i figured this out the hard way yesterday - accessing the parameters in a debugger totally worked but doing it in code caused stack too deep exceptions.

it would be cool to have the equivalent of a coerce_input callback with the irep_node (maybe analyze_input?) - this would make it cleaner to write validations that are conditional based on other sibling / parent nodes or nodes that have to be coerced first. i think that would make some code like this cleaner - right now i'm writing a giant FooValidationAnalyzer for a FooInputType - i expected i'll have to continue this pattern along even though a lot of the logic could be shared via the field.