promql: return NaN from `irate()` if second-last sample is NaN (#16199)

promql: return NaN from `irate()` if either of last two samples is NaN

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

---------

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

promql/functions.go

@@ -367,10 +367,11 @@ func instantValue(vals []parser.Value, args parser.Expressions, out Vector, isRa
 	}
 	switch {
 	case ss[1].H == nil && ss[0].H == nil:
-		if !isRate || ss[1].F >= ss[0].F {
-			// Gauge or counter without reset.
+		if !isRate || !(ss[1].F < ss[0].F) {
+			// Gauge, or counter without reset, or counter with NaN value.
 			resultSample.F = ss[1].F - ss[0].F
 		}
+
 		// In case of a counter reset, we leave resultSample at
 		// its current value, which is already ss[1].
 	case ss[1].H != nil && ss[0].H != nil:

promql/promqltest/testdata/functions.test

@@ -218,6 +218,7 @@ clear
 load 5m
 	http_requests_total{path="/foo"}	0+10x10
 	http_requests_total{path="/bar"}	0+10x5 0+10x5
+	http_requests_nan{}               1 NaN NaN 5 11
 	http_requests_histogram{path="/a"} {{sum:2 count:2}}+{{sum:3 count:3}}x5
 	http_requests_histogram{path="/b"} 0 0 {{sum:1 count:1}} {{sum:4 count:4}}
 	http_requests_histogram{path="/c"} 0 0 {{sum:1 count:1}} {{sum:4 count:4 counter_reset_hint:gauge}}
@@ -235,6 +236,9 @@ eval instant at 30m irate(http_requests_total[50m])
 	{path="/foo"} .03333333333333333333
 	{path="/bar"} 0
 
+eval range from 0 to 20m step 5m irate(http_requests_nan[15m1s])
+	{} _ NaN NaN NaN 0.02
+
 eval instant at 20m irate(http_requests_histogram{path="/a"}[20m])
 	{path="/a"} {{sum:0.01 count:0.01 counter_reset_hint:gauge}}
 
@@ -288,6 +292,7 @@ clear
 load 5m
 	http_requests{path="/foo"}	0 50 100 150
 	http_requests{path="/bar"}	0 50 100 50
+	http_requests_nan{}         1 NaN NaN 5 11
 	http_requests_histogram{path="/a"} {{sum:2 count:2 counter_reset_hint:gauge}}+{{sum:1 count:3 counter_reset_hint:gauge}}x5
 	http_requests_histogram{path="/b"} 0 0 {{sum:1 count:1 counter_reset_hint:gauge}} {{sum:2 count:2 counter_reset_hint:gauge}}
 	http_requests_histogram{path="/c"} 0 0 {{sum:1 count:1}} {{sum:2 count:2 counter_reset_hint:gauge}}
@@ -300,6 +305,9 @@ eval instant at 20m idelta(http_requests[20m])
 	{path="/foo"} 50
 	{path="/bar"} -50
 
+eval range from 0 to 20m step 5m idelta(http_requests_nan[15m1s])
+	{} _ NaN NaN NaN 6
+
 eval instant at 20m idelta(http_requests_histogram{path="/a"}[20m])
 	{path="/a"} {{sum:1 count:3 counter_reset_hint:gauge}}