1 files changed, 42 insertions, 0 deletions
diff --git a/app/graphql/types/base_field.rb b/app/graphql/types/base_field.rb
index 2b2ea64c00b..dd0d9105df6 100644
--- a/app/graphql/types/base_field.rb
+++ b/app/graphql/types/base_field.rb
@@ -3,5 +3,47 @@
 module Types
   class BaseField < GraphQL::Schema::Field
     prepend Gitlab::Graphql::Authorize
+
+    DEFAULT_COMPLEXITY = 1
+
+    def initialize(*args, **kwargs, &block)
+      kwargs[:complexity] ||= field_complexity(kwargs[:resolver_class])
+
+      super(*args, **kwargs, &block)
+    end
+
+    private
+
+    def field_complexity(resolver_class)
+      if resolver_class
+        field_resolver_complexity
+      else
+        DEFAULT_COMPLEXITY
+      end
+    end
+
+    def field_resolver_complexity
+      # Complexity can be either integer or proc. If proc is used then it's
+      # called when computing a query complexity and context and query
+      # arguments are available for computing complexity.  For resolvers we use
+      # proc because we set complexity depending on arguments and number of
+      # items which can be loaded.
+      proc do |ctx, args, child_complexity|
+        # Resolvers may add extra complexity depending on used arguments
+        complexity = child_complexity + self.resolver&.try(:resolver_complexity, args, child_complexity: child_complexity).to_i
+
+        field_defn = to_graphql
+
+        if field_defn.connection?
+          # Resolvers may add extra complexity depending on number of items being loaded.
+          page_size   = field_defn.connection_max_page_size || ctx.schema.default_max_page_size
+          limit_value = [args[:first], args[:last], page_size].compact.min
+          multiplier  = self.resolver&.try(:complexity_multiplier, args).to_f
+          complexity += complexity * limit_value * multiplier
+        end
+
+        complexity.to_i
+      end
+    end
   end
 end