promql: Fix issue where some native histogram-related annotations are not emitted by `rate` (#14575)

Signed-off-by: Charles Korn <charles.korn@grafana.com>

promql/functions.go

@@ -97,9 +97,10 @@ func extrapolatedRate(vals []parser.Value, args parser.Expressions, enh *EvalNod
 		lastT = samples.Histograms[numSamplesMinusOne].T
 		var newAnnos annotations.Annotations
 		resultHistogram, newAnnos = histogramRate(samples.Histograms, isCounter, metricName, args[0].PositionRange())
+		annos.Merge(newAnnos)
 		if resultHistogram == nil {
 			// The histograms are not compatible with each other.
-			return enh.Out, annos.Merge(newAnnos)
+			return enh.Out, annos
 		}
 	case len(samples.Floats) > 1:
 		numSamplesMinusOne = len(samples.Floats) - 1
@@ -189,6 +190,12 @@ func histogramRate(points []HPoint, isCounter bool, metricName string, pos posra
 
 	var annos annotations.Annotations
 
+	// We check for gauge type histograms in the loop below, but the loop below does not run on the first and last point,
+	// so check the first and last point now.
+	if isCounter && (prev.CounterResetHint == histogram.GaugeType || last.CounterResetHint == histogram.GaugeType) {
+		annos.Add(annotations.NewNativeHistogramNotCounterWarning(metricName, pos))
+	}
+
 	// First iteration to find out two things:
 	// - What's the smallest relevant schema?
 	// - Are all data points histograms?
@@ -241,7 +248,7 @@ func histogramRate(points []HPoint, isCounter bool, metricName string, pos posra
 	}
 
 	h.CounterResetHint = histogram.GaugeType
-	return h.Compact(0), nil
+	return h.Compact(0), annos
 }
 
 // === delta(Matrix parser.ValueTypeMatrix) (Vector, Annotations) ===

promql/promqltest/testdata/native_histograms.test

@@ -748,3 +748,17 @@ eval instant at 5m histogram_quantile(0.5, custom_buckets_histogram)
 
 eval instant at 5m sum(custom_buckets_histogram)
     {} {{schema:-53 sum:5 count:4 custom_values:[5 10] buckets:[1 2 1]}}
+
+clear
+
+# Test 'this native histogram metric is not a gauge' warning for rate
+load 30s
+    some_metric {{schema:0 sum:1 count:1 buckets:[1] counter_reset_hint:gauge}} {{schema:0 sum:2 count:2 buckets:[2] counter_reset_hint:gauge}} {{schema:0 sum:3 count:3 buckets:[3] counter_reset_hint:gauge}}
+
+# Test the case where we only have two points for rate
+eval_warn instant at 30s rate(some_metric[30s])
+    {} {{count:0.03333333333333333 sum:0.03333333333333333 buckets:[0.03333333333333333]}}
+
+# Test the case where we have more than two points for rate
+eval_warn instant at 1m rate(some_metric[1m])
+    {} {{count:0.03333333333333333 sum:0.03333333333333333 buckets:[0.03333333333333333]}}