Do no re-use result slice in chunkSetToSeriesSet

This is required to preserve the interface property of SeriesSet that says
"At returns full series. Returned series should be iterable even after Next is called."

Signed-off-by: sniper91 <kevinzhao91@outlook.com>

storage/series.go

@@ -205,7 +205,7 @@ func (c *chunkSetToSeriesSet) Next() bool {
 	}
 
 	c.iter = c.ChunkSeriesSet.At().Iterator(c.iter)
-	c.sameSeriesChunks = c.sameSeriesChunks[:0]
+	c.sameSeriesChunks = nil
 
 	for c.iter.Next() {
 		c.sameSeriesChunks = append(

storage/series_test.go

@@ -18,7 +18,9 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/tsdb/chunkenc"
+	"github.com/prometheus/prometheus/tsdb/tsdbutil"
 )
 
 func TestListSeriesIterator(t *testing.T) {
@@ -65,3 +67,61 @@ func TestListSeriesIterator(t *testing.T) {
 	// And we don't go back. (This exposes issue #10027.)
 	require.Equal(t, chunkenc.ValNone, it.Seek(2))
 }
+
+// TestSeriesSetToChunkSet test the property of SeriesSet that says
+// returned series should be iterable even after Next is called.
+func TestChunkSeriesSetToSeriesSet(t *testing.T) {
+	series := []struct {
+		lbs     labels.Labels
+		samples []tsdbutil.Sample
+	}{
+		{
+			lbs: labels.Labels{
+				{Name: "__name__", Value: "up"},
+				{Name: "instance", Value: "localhost:8080"},
+			},
+			samples: []tsdbutil.Sample{
+				sample{t: 1, v: 1},
+				sample{t: 2, v: 2},
+				sample{t: 3, v: 3},
+				sample{t: 4, v: 4},
+			},
+		}, {
+			lbs: labels.Labels{
+				{Name: "__name__", Value: "up"},
+				{Name: "instance", Value: "localhost:8081"},
+			},
+			samples: []tsdbutil.Sample{
+				sample{t: 1, v: 2},
+				sample{t: 2, v: 3},
+				sample{t: 3, v: 4},
+				sample{t: 4, v: 5},
+				sample{t: 5, v: 6},
+				sample{t: 6, v: 7},
+			},
+		},
+	}
+	var chunkSeries []ChunkSeries
+	for _, s := range series {
+		chunkSeries = append(chunkSeries, NewListChunkSeriesFromSamples(s.lbs, s.samples))
+	}
+	css := NewMockChunkSeriesSet(chunkSeries...)
+
+	ss := NewSeriesSetFromChunkSeriesSet(css)
+	var ssSlice []Series
+	for ss.Next() {
+		ssSlice = append(ssSlice, ss.At())
+	}
+	require.Len(t, ssSlice, 2)
+	var iter chunkenc.Iterator
+	for i, s := range ssSlice {
+		require.EqualValues(t, series[i].lbs, s.Labels())
+		iter = s.Iterator(iter)
+		j := 0
+		for iter.Next() == chunkenc.ValFloat {
+			ts, v := iter.At()
+			require.EqualValues(t, series[i].samples[j], sample{t: ts, v: v})
+			j++
+		}
+	}
+}