1 files changed, 33 insertions, 0 deletions
diff --git a/app/graphql/resolvers/project_merge_requests_resolver.rb b/app/graphql/resolvers/project_merge_requests_resolver.rb
index 830649d5e52..9628a6dfd7a 100644
--- a/app/graphql/resolvers/project_merge_requests_resolver.rb
+++ b/app/graphql/resolvers/project_merge_requests_resolver.rb
@@ -6,5 +6,38 @@ module Resolvers
     accept_assignee
     accept_author
     accept_reviewer
+
+    def resolve(**args)
+      scope = super
+
+      if only_count_is_selected_with_merged_at_filter?(args) && Feature.enabled?(:optimized_merge_request_count_with_merged_at_filter, default_enabled: :yaml)
+        MergeRequest::MetricsFinder
+          .new(current_user, args.merge(target_project: project))
+          .execute
+      else
+        scope
+      end
+    end
+
+    def only_count_is_selected_with_merged_at_filter?(args)
+      return unless lookahead
+
+      argument_names = args.compact.except(:lookahead, :sort, :merged_before, :merged_after).keys
+
+      # no extra filtering arguments are provided
+      return unless argument_names.empty?
+      return unless args[:merged_after] || args[:merged_before]
+
+      # Detecting a specific query pattern:
+      # mergeRequests(mergedAfter: "X", mergedBefore: "Y") {
+      #   count
+      #   totalTimeToMerge
+      # }
+      allowed_selected_fields = [:count, :total_time_to_merge]
+      selected_fields = lookahead.selections.map(&:field).map(&:original_name) - [:__typename] # ignore __typename meta field
+
+      # only the allowed_selected_fields are present
+      (selected_fields - allowed_selected_fields).empty?
+    end
   end
 end