promql: set CounterResetHint after rate and sum

Signed-off-by: Trevor Whitney <trevorjwhitney@gmail.com>

model/histogram/float_histogram.go

@@ -192,6 +192,8 @@ func (h *FloatHistogram) Scale(factor float64) *FloatHistogram {
 //
 // This method returns a pointer to the receiving histogram for convenience.
 func (h *FloatHistogram) Add(other *FloatHistogram) *FloatHistogram {
+	// TODO(trevorwhitney): If other.CounterResetHint != h.CounterResetHint then
+	// we should return some warning.
 	otherZeroCount := h.reconcileZeroBuckets(other)
 	h.ZeroCount += otherZeroCount
 	h.Count += other.Count
@@ -438,6 +440,15 @@ func (h *FloatHistogram) Compact(maxEmptyBuckets int) *FloatHistogram {
 // information can be read directly from there rather than be detected each time
 // again.
 func (h *FloatHistogram) DetectReset(previous *FloatHistogram) bool {
+	if h.CounterResetHint == CounterReset {
+		return true
+	}
+	if h.CounterResetHint == NotCounterReset {
+		return false
+	}
+	// In all other cases of CounterResetHint, we go on as we would otherwise.
+	// Even in the GaugeHistogram case, we pretend this is a counter histogram
+	// for consistency.
 	if h.Count < previous.Count {
 		return true
 	}

promql/engine_test.go

@@ -3155,8 +3155,7 @@ func TestNativeHistogramRate(t *testing.T) {
 	require.Len(t, vector, 1)
 	actualHistogram := vector[0].H
 	expectedHistogram := &histogram.FloatHistogram{
-		// TODO(beorn7): This should be GaugeType. Change it once supported by PromQL.
+		CounterResetHint: histogram.GaugeType,
-		CounterResetHint: histogram.NotCounterReset,
 		Schema:           1,
 		ZeroThreshold:    0.001,
 		ZeroCount:        1. / 15.,
@@ -3200,8 +3199,7 @@ func TestNativeFloatHistogramRate(t *testing.T) {
 	require.Len(t, vector, 1)
 	actualHistogram := vector[0].H
 	expectedHistogram := &histogram.FloatHistogram{
-		// TODO(beorn7): This should be GaugeType. Change it once supported by PromQL.
+		CounterResetHint: histogram.GaugeType,
-		CounterResetHint: histogram.NotCounterReset,
 		Schema:           1,
 		ZeroThreshold:    0.001,
 		ZeroCount:        1. / 15.,

promql/functions.go

@@ -187,6 +187,7 @@ func histogramRate(points []Point, isCounter bool) *histogram.FloatHistogram {
 		if curr == nil {
 			return nil // Range contains a mix of histograms and floats.
 		}
+		// TODO(trevorwhitney): Check if isCounter is consistent with curr.CounterResetHint.
 		if !isCounter {
 			continue
 		}
@@ -208,6 +209,8 @@ func histogramRate(points []Point, isCounter bool) *histogram.FloatHistogram {
 			prev = curr
 		}
 	}
+
+	h.CounterResetHint = histogram.GaugeType
 	return h.Compact(0)
 }