Fixed sampleRingIterator for mixed histograms

Signed-off-by: Sebastian Rabenhorst <sebastian.rabenhorst@shopify.com>

Fixed sampleRingIterator for mixed histograms

Signed-off-by: Sebastian Rabenhorst <sebastian.rabenhorst@shopify.com>

Fixed lint

storage/buffer.go

@@ -332,9 +332,11 @@ func (it *sampleRingIterator) Next() chunkenc.ValueType {
 	switch s.Type() {
 	case chunkenc.ValHistogram:
 		it.h = s.H()
+		it.fh = nil
 		return chunkenc.ValHistogram
 	case chunkenc.ValFloatHistogram:
 		it.fh = s.FH()
+		it.h = nil
 		return chunkenc.ValFloatHistogram
 	default:
 		it.f = s.F()

storage/buffer_test.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/tsdb/chunkenc"
+	"github.com/prometheus/prometheus/tsdb/tsdbutil"
 )
 
 func TestSampleRing(t *testing.T) {
@@ -180,6 +181,28 @@ func TestBufferedSeriesIteratorNoBadAt(t *testing.T) {
 	it.Next()
 }
 
+func TestBufferedSeriesIteratorMixedHistograms(t *testing.T) {
+	histograms := tsdbutil.GenerateTestHistograms(2)
+
+	it := NewBufferIterator(NewListSeriesIterator(samples{
+		fhSample{t: 1, fh: histograms[0].ToFloat()},
+		hSample{t: 2, h: histograms[1]},
+	}), 2)
+
+	require.Equal(t, chunkenc.ValNone, it.Seek(3))
+	require.NoError(t, it.Err())
+
+	buf := it.Buffer()
+
+	require.Equal(t, chunkenc.ValFloatHistogram, buf.Next())
+	_, fh := buf.AtFloatHistogram()
+	require.Equal(t, histograms[0].ToFloat(), fh)
+
+	require.Equal(t, chunkenc.ValHistogram, buf.Next())
+	_, fh = buf.AtFloatHistogram()
+	require.Equal(t, histograms[1].ToFloat(), fh)
+}
+
 func BenchmarkBufferedSeriesIterator(b *testing.B) {
 	// Simulate a 5 minute rate.
 	it := NewBufferIterator(newFakeSeriesIterator(int64(b.N), 30), 5*60)