better error handling for required fields in an input object

[modosc]

consider something like:

input FooInput {
  bar: BarInput!
}
input BarInput {
  baz: BazInput!
}
input BazInput {
  bat: String!
}

if i leave out bat from my input i get an error like:

{      "message": "Argument 'baz' on InputObject 'BarInput' has an invalid value. Expected type 'BazInput!'.",
      "locations": [
        {
          "line": null,
          "column": null
        }
      ],
      "fields": [
        "mutation FooMutation",
        "fooMutation",
        "input",
        "bar",
        "baz"
      ]
    },

(sorry this may not be exact, i'm transposing from a work project)

i'd expect the missing required field (bat) to be the field referenced in the error message and the path, but currently that's not the case. i think the issue is here:

https://github.com/rmosolgo/graphql-ruby/blob/master/lib/graphql/static_validation/literal_validator.rb#L26

since there's no actual ast node for the missing field, the error message that's generated comes from the parent input object.

[rmosolgo]

Thanks for the feature request! I agree that the validation messages could use work, but I haven't been able to prioritize it (see #160).