Fix building of GraphQL queries arguments hash

lib/datadog/appsec/contrib/graphql/gateway/multiplex.rb

@@ -55,7 +55,9 @@ def build_arguments_hash
 
             def arguments_from_selections(selections, query_variables, args_hash)
               selections.each do |selection|
-                next unless selection.is_a?(::GraphQL::Language::Nodes::Field)
+                # rubocop:disable Style/ClassEqualityComparison
+                next unless selection.class.to_s == Integration::AST_NODE_CLASS_NAMES[:field]
+                # rubocop:enable Style/ClassEqualityComparison
 
                 selection_name = selection.alias || selection.name
 
@@ -73,7 +75,9 @@ def arguments_from_selections(selections, query_variables, args_hash)
 
             def arguments_from_directives(directives, query_variables)
               directives.each_with_object({}) do |directive, args_hash|
-                next unless directive.is_a?(::GraphQL::Language::Nodes::Directive)
+                # rubocop:disable Style/ClassEqualityComparison
+                next unless directive.class.to_s == Integration::AST_NODE_CLASS_NAMES[:directive]
+                # rubocop:enable Style/ClassEqualityComparison
 
                 args_hash[directive.name] = arguments_hash(directive.arguments, query_variables)
               end
@@ -86,12 +90,12 @@ def arguments_hash(arguments, query_variables)
             end
 
             def argument_value(argument, query_variables)
-              case argument.value
-              when ::GraphQL::Language::Nodes::VariableIdentifier
+              case argument.value.class.to_s
+              when Integration::AST_NODE_CLASS_NAMES[:variable_identifier]
                 # we need to pass query.variables here instead of query.provided_variables,
                 # since #provided_variables don't know anything about variable default value
                 query_variables[argument.value.name]
-              when ::GraphQL::Language::Nodes::InputObject
+              when Integration::AST_NODE_CLASS_NAMES[:input_object]
                 arguments_hash(argument.value.arguments, query_variables)
               else
                 argument.value

lib/datadog/appsec/contrib/graphql/integration.rb

@@ -13,6 +13,13 @@ class Integration
 
           MINIMUM_VERSION = Gem::Version.new('2.0.19')
 
+          AST_NODE_CLASS_NAMES = {
+            field: 'GraphQL::Language::Nodes::Field',
+            directive: 'GraphQL::Language::Nodes::Directive',
+            variable_identifier: 'GraphQL::Language::Nodes::VariableIdentifier',
+            input_object: 'GraphQL::Language::Nodes::InputObject',
+          }.freeze
+
           register_as :graphql, auto_patch: false
 
           def self.version
@@ -24,13 +31,19 @@ def self.loaded?
           end
 
           def self.compatible?
-            super && version >= MINIMUM_VERSION
+            super && version >= MINIMUM_VERSION && ast_node_classes_defined?
           end
 
           def self.auto_instrument?
             true
           end
 
+          def self.ast_node_classes_defined?
+            AST_NODE_CLASS_NAMES.all? do |_, class_name|
+              Object.const_defined?(class_name)
+            end
+          end
+
           def patcher
             Patcher
           end

spec/datadog/appsec/contrib/graphql/gateway/multiplex_spec.rb

@@ -4,9 +4,7 @@
 require 'datadog/appsec/contrib/graphql/gateway/multiplex'
 
 RSpec.describe Datadog::AppSec::Contrib::GraphQL::Gateway::Multiplex do
-  subject(:dd_multiplex) do
-    described_class.new(multiplex)
-  end
+  subject(:dd_multiplex) { described_class.new(multiplex) }
 
   let(:schema) do
     # we are only testing how arguments are extracted from the queries,