app/vmselect/promql: return nan from minute(m) when m equals to nan

This aligns VictoriaMetrics behaviour with Prometheus behaviour.

The issue has been spotted in https://promlabs.com/promql-compliance-test-results/2020-12-01/victoriametrics/

app/vmselect/promql/exec_test.go

@@ -526,6 +526,17 @@ func TestExecSuccess(t *testing.T) {
 		resultExpected := []netstorage.Result{r}
 		f(q, resultExpected)
 	})
+	t.Run(`minute(series_with_NaNs)`, func(t *testing.T) {
+		t.Parallel()
+		q := `minute(time() <= 1200 or time() > 1600)`
+		r := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values: []float64{16, 20, nan, nan, 30, 33},
+			Timestamps: timestampsExpected,
+		}
+		resultExpected := []netstorage.Result{r}
+		f(q, resultExpected)
+	})
 	t.Run("rate({})", func(t *testing.T) {
 		t.Parallel()
 		q := `rate({})`

app/vmselect/promql/transform.go

@@ -265,6 +265,9 @@ func newTransformFuncDateTime(f func(t time.Time) int) transformFunc {
 		}
 		tf := func(values []float64) {
 			for i, v := range values {
+				if math.IsNaN(v) {
+					continue
+				}
 				t := time.Unix(int64(v), 0).UTC()
 				values[i] = float64(f(t))
 			}

docs/CHANGELOG.md

@@ -7,7 +7,9 @@
 * BUGFIX: return `nan` for `a >bool b` query when `a` equals to `nan` like Prometheus does. Previously `0` was returned in this case. This applies to any comparison operation
   with `bool` modifier. See [these docs](https://prometheus.io/docs/prometheus/latest/querying/operators/#comparison-binary-operators) for details.
 * BUGFIX: properly parse hex numbers in MetricsQL. Previously hex numbers with non-decimal digits such as `0x3b` couldn't be parsed.
-* BUGFIX: Handle `time() cmp_op metric` like Prometheus does - i.e. return `metric` value if `cmp_op` comparison is true. Previously `time()` value was returned.
+* BUGFIX: handle `time() cmp_op metric` like Prometheus does - i.e. return `metric` value if `cmp_op` comparison is true. Previously `time()` value was returned.
+* BUGFIX: return `nan` for `minute(m)` query when `m` equals to `nan` like Prometheus does. This applies to all the time-related functions such as `day_of_month`, `day_of_week`,
+  `days_in_month`, `hour`, `month` and `year`.
 
 
 # [v1.48.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.48.0)