GraphQL support for Notes created in discussions

A new `discussion_id` argument on the `createNote` mutation allows
people to create a note within that discussion.

The ability to lazy-load Discussions has been added, so
GraphQL.object_from_id can treat Discussions the same as AR objects and
batch load them.

https://gitlab.com/gitlab-org/gitlab-ce/issues/62826
https://gitlab.com/gitlab-org/gitlab-ee/issues/9489

1 files changed, 29 insertions, 0 deletions

diff --git a/app/graphql/mutations/notes/create/note.rb b/app/graphql/mutations/notes/create/note.rb
index 3c571a4538f..5236e48026e 100644
--- a/app/graphql/mutations/notes/create/note.rb
+++ b/app/graphql/mutations/notes/create/note.rb
@@ -5,6 +5,35 @@ module Mutations
     module Create
       class Note < Base
         graphql_name 'CreateNote'
+
+        argument :discussion_id,
+                  GraphQL::ID_TYPE,
+                  required: false,
+                  description: 'The global id of the discussion this note is in reply to'
+
+        private
+
+        def create_note_params(noteable, args)
+          discussion_id = nil
+
+          if args[:discussion_id]
+            discussion = GitlabSchema.object_from_id(args[:discussion_id])
+            authorize_discussion!(discussion)
+
+            discussion_id = discussion.id
+          end
+
+          super(noteable, args).merge({
+            in_reply_to_discussion_id: discussion_id
+          })
+        end
+
+        def authorize_discussion!(discussion)
+          unless Ability.allowed?(current_user, :read_note, discussion, scope: :user)
+            raise Gitlab::Graphql::Errors::ResourceNotAvailable,
+              "The discussion does not exist or you don't have permission to perform this action"
+          end
+        end
       end
     end
   end