Update note on ph values

pkg/streamingpromql/operators/functions/histograms.go

@@ -336,6 +336,8 @@ func (h *HistogramFunctionOverInstantVector) computeOutputSeriesForGroup(g *buck
 		if math.IsNaN(ph) || ph < 0 || ph > 1 {
 			// Even when ph is invalid we still return a series as BucketQuantile will return +/-Inf.
 			// So don't skip/continue the series, just emit a warning.
+			// Additionally, even if a point isn't returned, an annotation is emitted if ph is invalid
+			// at any step.
 			h.annotations.Add(annotations.NewInvalidQuantileWarning(ph, h.phArg.ExpressionPosition()))
 		}
 

pkg/streamingpromql/testdata/ours/classic_histograms.test

@@ -62,6 +62,21 @@ eval_warn range from 0m to 24m step 6m histogram_quantile(scalar(ph), series)
 
 clear
 
+# Test for invalid ph value where no points
+load 6m
+	series{le="0"}    0   _   0
+	series{le="2"}    1   _   1
+	series{le="4"}    2   _   2
+	series{le="6"}    3   _   3
+	series{le="+Inf"} 3   _   3
+	ph                0.5 NaN 0.9
+
+# Both engines output a warning even though there is no point where ph is also invalid.
+eval_warn range from 0m to 12m step 6m histogram_quantile(scalar(ph), series)
+	{} 3 _ 5.4
+
+clear
+
 # Test various mixed metric scenarios
 load 6m
 	series{host="a", le="0.1"}  2 _ 1 {{schema:0 sum:5 count:4 buckets:[2 2 2]}}