2 files changed, 37 insertions, 0 deletions
diff --git a/pkg/subsystem/entities.go b/pkg/subsystem/entities.go
index 1f7456e84..457e57a3e 100644
--- a/pkg/subsystem/entities.go
+++ b/pkg/subsystem/entities.go
@@ -44,6 +44,28 @@ func (subsystem *Subsystem) Emails() []string {
 	return ret
 }
 
+func FilterList(list []*Subsystem, filter func(*Subsystem) bool) []*Subsystem {
+	keep := map[*Subsystem]bool{}
+	for _, item := range list {
+		keep[item] = filter(item)
+	}
+	newList := []*Subsystem{}
+	for _, item := range list {
+		if !keep[item] {
+			continue
+		}
+		newParents := []*Subsystem{}
+		for _, p := range item.Parents {
+			if keep[p] {
+				newParents = append(newParents, p)
+			}
+		}
+		item.Parents = newParents
+		newList = append(newList, item)
+	}
+	return newList
+}
+
 // PathRule describes the part of the directory tree belonging to a single subsystem.
 type PathRule struct {
 	IncludeRegexp string
diff --git a/pkg/subsystem/entities_test.go b/pkg/subsystem/entities_test.go
index 58166b91b..81c970b65 100644
--- a/pkg/subsystem/entities_test.go
+++ b/pkg/subsystem/entities_test.go
@@ -39,3 +39,18 @@ func TestSubsystemEmails(t *testing.T) {
 		"a@list.com", "b@list.com", "c@list.com", "d@list.com", "d@person.com",
 	})
 }
+
+func TestFilterList(t *testing.T) {
+	parentParent := &Subsystem{}
+	parentA := &Subsystem{Parents: []*Subsystem{parentParent}}
+	parentB := &Subsystem{Parents: []*Subsystem{parentParent}}
+	entity := &Subsystem{Parents: []*Subsystem{parentA, parentB}}
+
+	newList := FilterList([]*Subsystem{parentA, parentB, parentParent, entity},
+		func(s *Subsystem) bool {
+			return s != parentB
+		},
+	)
+	assert.Len(t, newList, 3)
+	assert.ElementsMatch(t, entity.Parents, []*Subsystem{parentA})
+}