Fix Err fallout for graph/iterator.Comparison iterator

graph/iterator/value_comparison_iterator.go

@@ -51,6 +51,7 @@ type Comparison struct {
 	val    interface{}
 	qs     graph.QuadStore
 	result graph.Value
+	err    error
 }
 
 func NewComparison(sub graph.Iterator, op Operator, val interface{}, qs graph.QuadStore) *Comparison {
@@ -133,9 +134,16 @@ func (it *Comparison) Next() bool {
 			return true
 		}
 	}
+	if err := graph.Err(it.subIt); err != nil {
+		it.err = err
+	}
 	return false
 }
 
+func (it *Comparison) Err() error {
+	return it.err
+}
+
 // DEPRECATED
 func (it *Comparison) ResultTree() *graph.ResultTree {
 	return graph.NewResultTree(it.Result())

graph/iterator/value_comparison_iterator_test.go

@@ -15,6 +15,7 @@
 package iterator
 
 import (
+	"errors"
 	"reflect"
 	"testing"
 
@@ -118,3 +119,17 @@ func TestVCIContains(t *testing.T) {
 		}
 	}
 }
+
+func TestComparisonIteratorErr(t *testing.T) {
+	retErr := errors.New("unique")
+	errIt := newTestIterator(false, retErr)
+
+	vc := NewComparison(errIt, compareLT, int64(2), simpleStore)
+
+	if vc.Next() != false {
+		t.Errorf("Comparison iterator did not pass through initial 'false'")
+	}
+	if vc.Err() != retErr {
+		t.Errorf("Comparison iterator did not pass through underlying Err")
+	}
+}