Flatten aggregated error when generating Error() string

staging/src/k8s.io/apimachinery/pkg/util/errors/errors.go

@@ -71,23 +71,38 @@ func (agg aggregate) Error() string {
 	}
 	seenerrs := sets.NewString()
 	result := ""
-	for _, err := range agg {
+	agg.visit(func(err error) {
 		msg := err.Error()
 		if seenerrs.Has(msg) {
-			continue
+			return
 		}
 		seenerrs.Insert(msg)
 		if len(seenerrs) > 1 {
 			result += ", "
 		}
 		result += msg
-	}
+	})
 	if len(seenerrs) == 1 {
 		return result
 	}
 	return "[" + result + "]"
 }
 
+func (agg aggregate) visit(f func(err error)) {
+	for _, err := range agg {
+		switch err := err.(type) {
+		case aggregate:
+			err.visit(f)
+		case Aggregate:
+			for _, nestedErr := range err.Errors() {
+				f(nestedErr)
+			}
+		default:
+			f(err)
+		}
+	}
+}
+
 // Errors is part of the Aggregate interface.
 func (agg aggregate) Errors() []error {
 	return []error(agg)

staging/src/k8s.io/apimachinery/pkg/util/errors/errors_test.go

@@ -179,6 +179,38 @@ func TestDedupePluralAggregate(t *testing.T) {
 	}
 }
 
+func TestFlattenAndDedupeAggregate(t *testing.T) {
+	var slice []error = []error{fmt.Errorf("abc"), fmt.Errorf("abc"), NewAggregate([]error{fmt.Errorf("abc")})}
+	var agg Aggregate
+
+	agg = NewAggregate(slice)
+	if agg == nil {
+		t.Errorf("expected non-nil")
+	}
+	if s := agg.Error(); s != "abc" {
+		t.Errorf("expected 'abc', got %q", s)
+	}
+	if s := agg.Errors(); len(s) != 3 {
+		t.Errorf("expected three-elements slice, got %#v", s)
+	}
+}
+
+func TestFlattenAggregate(t *testing.T) {
+	var slice []error = []error{fmt.Errorf("abc"), fmt.Errorf("abc"), NewAggregate([]error{fmt.Errorf("abc"), fmt.Errorf("def"), NewAggregate([]error{fmt.Errorf("def"), fmt.Errorf("ghi")})})}
+	var agg Aggregate
+
+	agg = NewAggregate(slice)
+	if agg == nil {
+		t.Errorf("expected non-nil")
+	}
+	if s := agg.Error(); s != "[abc, def, ghi]" {
+		t.Errorf("expected '[abc, def, ghi]', got %q", s)
+	}
+	if s := agg.Errors(); len(s) != 3 {
+		t.Errorf("expected three-elements slice, got %#v", s)
+	}
+}
+
 func TestFilterOut(t *testing.T) {
 	testCases := []struct {
 		err      error