Fix Err fallout for graph/iterator.HasA iterator

graph/iterator/hasa_iterator.go

@@ -51,6 +51,7 @@ type HasA struct {
 	dir       quad.Direction
 	resultIt  graph.Iterator
 	result    graph.Value
+	err       error
 	runstats  graph.IteratorStats
 }
 
@@ -202,6 +203,9 @@ func (it *HasA) Next() bool {
 	it.resultIt = &Null{}
 
 	if !graph.Next(it.primaryIt) {
+		if err := graph.Err(it.primaryIt); err != nil {
+			it.err = err
+		}
 		return graph.NextLogOut(it, 0, false)
 	}
 	tID := it.primaryIt.Result()
@@ -210,6 +214,10 @@ func (it *HasA) Next() bool {
 	return graph.NextLogOut(it, val, true)
 }
 
+func (it *HasA) Err() error {
+	return it.err
+}
+
 func (it *HasA) Result() graph.Value {
 	return it.result
 }

graph/iterator/hasa_iterator_test.go

@@ -0,0 +1,37 @@
+// Copyright 2014 The Cayley Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package iterator
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/google/cayley/quad"
+)
+
+func TestHasAIteratorErr(t *testing.T) {
+	retErr := errors.New("unique")
+	errIt := newTestIterator(false, retErr)
+
+	// TODO(andrew-d): pass a non-nil quadstore
+	hasa := NewHasA(nil, errIt, quad.Subject)
+
+	if hasa.Next() != false {
+		t.Errorf("HasA iterator did not pass through initial 'false'")
+	}
+	if hasa.Err() != retErr {
+		t.Errorf("HasA iterator did not pass through underlying Err")
+	}
+}