Fix a bug calculating artifact size for project statistics

app/models/project_statistics.rb

@@ -37,7 +37,7 @@ class ProjectStatistics < ActiveRecord::Base
   def update_build_artifacts_size
     self.build_artifacts_size =
       project.builds.sum(:artifacts_size) +
-      Ci::JobArtifact.artifacts_size_for(self)
+      Ci::JobArtifact.artifacts_size_for(self.project)
   end
 
   def update_storage_size

changelogs/unreleased/42154-fix-artifact-size-calc.yml

@@ -0,0 +1,5 @@
+---
+title: Fix a bug calculating artifact size for project statistics
+merge_request: 16539
+author:
+type: fixed

spec/models/project_statistics_spec.rb

@@ -146,6 +146,12 @@ describe ProjectStatistics do
 
         expect(statistics.build_artifacts_size).to be(106365)
       end
+
+      it 'calculates related build artifacts by project' do
+        expect(Ci::JobArtifact).to receive(:artifacts_size_for).with(project) { 0 }
+
+        statistics.update_build_artifacts_size
+      end
     end
 
     context 'when legacy artifacts are used' do