1 files changed, 32 insertions, 0 deletions
diff --git a/lib/api/validations/check_assignees_count.rb b/lib/api/validations/check_assignees_count.rb
new file mode 100644
index 00000000000..836ec936b31
--- /dev/null
+++ b/lib/api/validations/check_assignees_count.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module API
+  module Validations
+    class CheckAssigneesCount < Grape::Validations::Base
+      def self.coerce
+        lambda do |value|
+          case value
+          when String, Array
+            Array.wrap(value)
+          else
+            []
+          end
+        end
+      end
+
+      def validate_param!(attr_name, params)
+        return if param_allowed?(attr_name, params)
+
+        raise Grape::Exceptions::Validation,
+              params: [@scope.full_name(attr_name)],
+              message: "allows one value, but found #{params[attr_name].size}: #{params[attr_name].join(", ")}"
+      end
+
+      private
+
+      def param_allowed?(attr_name, params)
+        params[attr_name].size <= 1
+      end
+    end
+  end
+end