CE backport for changes in EE MR 14292

EE MR https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14292
https://gitlab.com/gitlab-org/gitlab-ee/issues/9491

lib/gitlab/graphql/find_argument_in_parent.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Graphql
+    module FindArgumentInParent
+      # Searches up the GraphQL AST and returns the first matching argument
+      # passed to a node
+      def self.find(parent, argument, limit_depth: nil)
+        argument = argument.to_s.camelize(:lower).to_sym
+        depth = 0
+
+        while parent.respond_to?(:parent)
+          args = node_args(parent)
+          return args[argument] if args.key?(argument)
+
+          depth += 1
+          return if limit_depth && depth >= limit_depth
+
+          parent = parent.parent
+        end
+      end
+
+      class << self
+        private
+
+        def node_args(node)
+          node.irep_node.arguments
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/graphql/find_argument_in_parent_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Graphql::FindArgumentInParent do
+  describe '#find' do
+    def build_node(parent = nil, args: {})
+      props = { irep_node: double(arguments: args) }
+      props[:parent] = parent if parent # The root node shouldn't respond to parent
+
+      double(props)
+    end
+
+    let(:parent) do
+      build_node(
+        build_node(
+          build_node(
+            build_node,
+            args: { myArg: 1 }
+          )
+        )
+      )
+    end
+    let(:arg_name) { :my_arg }
+
+    it 'searches parents and returns the argument' do
+      expect(described_class.find(parent, :my_arg)).to eq(1)
+    end
+
+    it 'can find argument when passed in as both Ruby and GraphQL-formatted symbols and strings' do
+      [:my_arg, :myArg, 'my_arg', 'myArg'].each do |arg|
+        expect(described_class.find(parent, arg)).to eq(1)
+      end
+    end
+
+    it 'returns nil if no arguments found in parents' do
+      expect(described_class.find(parent, :bar)).to eq(nil)
+    end
+
+    it 'can limit the depth it searches to' do
+      expect(described_class.find(parent, :my_arg, limit_depth: 1)).to eq(nil)
+    end
+  end
+end