Expose permissions on types in GraphQL

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

2 files changed, 25 insertions, 1 deletions

diff --git a/lib/gitlab/graphql/expose_permissions.rb b/lib/gitlab/graphql/expose_permissions.rb
new file mode 100644
index 00000000000..e3779995406
--- /dev/null
+++ b/lib/gitlab/graphql/expose_permissions.rb
@@ -0,0 +1,15 @@
+module Gitlab
+  module Graphql
+    module ExposePermissions
+      extend ActiveSupport::Concern
+      prepended do
+        def self.expose_permissions(permission_type, description: 'Permissions for the current user on the resource')
+          field :user_permissions, permission_type,
+                description: description,
+                null: false,
+                resolve: -> (obj, _, _) { obj }
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/graphql/present/instrumentation.rb b/lib/gitlab/graphql/present/instrumentation.rb
index 1688262974b..6f2b26c9676 100644
--- a/lib/gitlab/graphql/present/instrumentation.rb
+++ b/lib/gitlab/graphql/present/instrumentation.rb
@@ -10,9 +10,18 @@ module Gitlab
           old_resolver = field.resolve_proc
 
           resolve_with_presenter = -> (presented_type, args, context) do
+            # We need to wrap the original presentation type into a type that
+            # uses the presenter as an object.
             object = presented_type.object
+
+            if object.is_a?(presented_in.presenter_class)
+              next old_resolver.call(presented_type, args, context)
+            end
+
             presenter = presented_in.presenter_class.new(object, **context.to_h)
-            old_resolver.call(presenter, args, context)
+            wrapped = presented_type.class.new(presenter, context)
+
+            old_resolver.call(wrapped, args, context)
           end
 
           field.redefine do