db: add NewIterWithContext to Reader

batch.go

@@ -1088,16 +1088,16 @@ func (b *Batch) SetRepr(data []byte) error {
 // later mutations. Its view can be refreshed via RefreshBatchSnapshot or
 // SetOptions().
 func (b *Batch) NewIter(o *IterOptions) (*Iterator, error) {
-	return b.NewIterWithContext(context.Background(), o), nil
+	return b.NewIterWithContext(context.Background(), o)
 }
 
 // NewIterWithContext is like NewIter, and additionally accepts a context for
 // tracing.
-func (b *Batch) NewIterWithContext(ctx context.Context, o *IterOptions) *Iterator {
+func (b *Batch) NewIterWithContext(ctx context.Context, o *IterOptions) (*Iterator, error) {
 	if b.index == nil {
-		return &Iterator{err: ErrNotIndexed}
+		return &Iterator{err: ErrNotIndexed}, nil
 	}
-	return b.db.newIter(ctx, b, snapshotIterOpts{}, o)
+	return b.db.newIter(ctx, b, snapshotIterOpts{}, o), nil
 }
 
 // newInternalIter creates a new internalIterator that iterates over the

db.go

@@ -77,6 +77,10 @@ type Reader interface {
 	// SeekLT, First or Last.
 	NewIter(o *IterOptions) (*Iterator, error)
 
+	// NewIterWithContext is like NewIter, and additionally accepts a context
+	// for tracing.
+	NewIterWithContext(ctx context.Context, o *IterOptions) (*Iterator, error)
+
 	// Close closes the Reader. It may or may not close any underlying io.Reader
 	// or io.Writer, depending on how the DB was created.
 	//

db_test.go

@@ -1467,7 +1467,8 @@ func TestTracing(t *testing.T) {
 
 	tracer.buf.Reset()
 	b := d.NewIndexedBatch()
-	iter = b.NewIterWithContext(ctx, nil)
+	iter, err = b.NewIterWithContext(ctx, nil)
+	require.NoError(t, err)
 	iter.SeekGE([]byte("hello"))
 	iter.Close()
 	require.Equal(t, iterTraceString, tracer.buf.String())