[GraphQL::Schema::Visibility] Change in Static Validation of Variable Types

When using the GraphQL::Schema::Visibility plugin, the behavior of how static validation of variables changes. Consider the following example schema:

class MyInputType < GraphQL::Schema::InputObject
  argument :some_field, String, required: true
end

class MyInternalMutation < GraphQL::Schema::Mutation
  argument :input, MyInputType, required: true

  field :success, Boolean, null: false

  def self.visible?(ctx)
    ctx[:internal_client] == true
  end

  def resolve(input:)
    { success: true }
  end
end

class MutationRoot < GraphQL::Schema::Object
  field :my_mutation, mutation: MyInternalMutation
end

class MySchema < GraphQL::Schema
  use(GraphQL::Schema::Visibility)

  mutation(MutationRoot)
end

query = <<~GRAPHQL
  mutation MyMutation($input: MyInput!) {
    myMutation(input: $input) {
      success
    }
  }
GRAPHQL

result = MySchema.execute(
  query,
  context: { internal_client: false },
  variables: { "input" => { "someField" => "someValue" } },
)

When operating in GraphQL::Schema::Warden mode, the following expected error is returned:

{"errors":[{"message":"Field 'myMutation' doesn't exist on type 'MutationRoot'","locations":[{"line":2,"column":3}],"path":["mutation MyMutation","myMutation"],"extensions":{"code":"undefinedField","typeName":"MutationRoot","fieldName":"myMutation"}},{"message":"Variable $input is declared by MyMutation but not used","locations":[{"line":1,"column":1}],"path":["mutation MyMutation"],"extensions":{"code":"variableNotUsed","variableName":"input"}}]}

However, with visibility, we get a different error stating that the otherwise public input type does not exist:

{"errors":[{"message":"MyInput isn't a defined input type (on $input)","locations":[{"line":1,"column":21}],"path":["mutation MyMutation"],"extensions":{"code":"variableRequiresValidType","typeName":"MyInput","variableName":"input"}},{"message":"Field 'myMutation' doesn't exist on type 'MutationRoot'","locations":[{"line":2,"column":3}],"path":["mutation MyMutation","myMutation"],"extensions":{"code":"undefinedField","typeName":"MutationRoot","fieldName":"myMutation"}},{"message":"Variable $input is declared by MyMutation but not used","locations":[{"line":1,"column":1}],"path":["mutation MyMutation"],"extensions":{"code":"variableNotUsed","variableName":"input"}}]}

It is unclear whether this is a regression or just a change in behavior. I believe it is due to the fact that MyInput is unreachable by any public path, but this was not something enforced by warden.

Start by reproducing the example with GraphQL::Schema::Visibility enabled and compare it with GraphQL::Schema::Warden mode. Trace how static variable-type validation handles the unreachable MyInput type, then add or update regression coverage so the intended validation behavior is explicit.