Expose permissions on types in GraphQL

This adds a reusable way to expose permissions for a user to types in
GraphQL.

1 files changed, 38 insertions, 0 deletions

diff --git a/app/graphql/types/permission_types/base_permission_type.rb b/app/graphql/types/permission_types/base_permission_type.rb
new file mode 100644
index 00000000000..934ed572e56
--- /dev/null
+++ b/app/graphql/types/permission_types/base_permission_type.rb
@@ -0,0 +1,38 @@
+module Types
+  module PermissionTypes
+    class BasePermissionType < BaseObject
+      extend Gitlab::Allowable
+
+      RESOLVING_KEYWORDS = [:resolver, :method, :hash_key, :function].to_set.freeze
+
+      def self.abilities(*abilities)
+        abilities.each { |ability| ability_field(ability) }
+      end
+
+      def self.ability_field(ability, **kword_args)
+        unless resolving_keywords?(kword_args)
+          kword_args[:resolve] ||= -> (object, args, context) do
+            can?(context[:current_user], ability, object, args.to_h)
+          end
+        end
+
+        permission_field(ability, **kword_args)
+      end
+
+      def self.permission_field(name, **kword_args)
+        kword_args = kword_args.reverse_merge(
+          name: name,
+          type: GraphQL::BOOLEAN_TYPE,
+          description: "Whether or not a user can perform `#{name}` on this resource",
+          null: false)
+
+        field(**kword_args)
+      end
+
+      def self.resolving_keywords?(arguments)
+        RESOLVING_KEYWORDS.intersect?(arguments.keys.to_set)
+      end
+      private_class_method :resolving_keywords?
+    end
+  end
+end