Make rate possible non-counter annotation consistent (#14910)

* Make rate possible non-counter annotation consistent

Previously a PossibleNonCounterInfo annotation would be left in cases
where a range-vector selects 1 float data point, even if no more points
are selected in order to calculate a rate.

This change ensures an output float exists before emitting such an
annotation.

This fixes an inconsistency where a series with mixed data (ie, a float
and a native histogram) would emit an annotation without any points.

For example,

```

load 1m
series{label="a"} 1 {{schema:1 sum:10 count:5 buckets:[1 2 3]}}

eval instant at 1m rate(series[1m1s])

```

Would have a PossibleNonCounterInfo annotation.

Wheras

```

load 1m
series{label="a"} {{schema:1 sum:10 count:5 buckets:[1 2 3]}} {{schema:1 sum:15 count:10 buckets:[1 2 3]}}

eval instant at 1m rate(series[1m1s])

```

Would not. 

---------

Signed-off-by: Joshua Hesketh <josh@nitrotech.org>

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## unreleased
+
+* [BUGFIX] PromQL: Only return "possible non-counter" annotation when `rate` returns points. #14910
+
 ## 3.0.0-beta.0 / 2024-09-05
 
 Release 3.0.0-beta.0 includes new features such as a brand new UI and UTF-8 support enabled by default. As a new major version, several breaking changes are introduced. The breaking changes are mainly around the removal of deprecated feature flags and CLI arguments, and the full list can be found below. Most users should be able to try this release out of the box without any configuration changes.

promql/engine.go

@@ -1742,9 +1742,8 @@ func (ev *evaluator) eval(ctx context.Context, expr parser.Expr) (parser.Value,
 			ev.samplesStats.UpdatePeak(ev.currentSamples)
 
 			if e.Func.Name == "rate" || e.Func.Name == "increase" {
-				samples := inMatrix[0]
-				metricName := samples.Metric.Get(labels.MetricName)
-				if metricName != "" && len(samples.Floats) > 0 &&
+				metricName := inMatrix[0].Metric.Get(labels.MetricName)
+				if metricName != "" && len(ss.Floats) > 0 &&
 					!strings.HasSuffix(metricName, "_total") &&
 					!strings.HasSuffix(metricName, "_sum") &&
 					!strings.HasSuffix(metricName, "_count") &&

promql/engine_test.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 	"sort"
 	"strconv"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -3708,3 +3709,75 @@ histogram {{sum:4 count:4 buckets:[2 2]}} {{sum:6 count:6 buckets:[3 3]}} {{sum:
 		},
 	})
 }
+
+func TestRateAnnotations(t *testing.T) {
+	testCases := map[string]struct {
+		data                       string
+		expr                       string
+		expectedWarningAnnotations []string
+		expectedInfoAnnotations    []string
+	}{
+		"info annotation when two samples are selected": {
+			data: `
+				series 1 2
+			`,
+			expr:                       "rate(series[1m1s])",
+			expectedWarningAnnotations: []string{},
+			expectedInfoAnnotations: []string{
+				`PromQL info: metric might not be a counter, name does not end in _total/_sum/_count/_bucket: "series" (1:6)`,
+			},
+		},
+		"no info annotations when no samples": {
+			data: `
+				series
+			`,
+			expr:                       "rate(series[1m1s])",
+			expectedWarningAnnotations: []string{},
+			expectedInfoAnnotations:    []string{},
+		},
+		"no info annotations when selecting one sample": {
+			data: `
+				series 1 2
+			`,
+			expr:                       "rate(series[10s])",
+			expectedWarningAnnotations: []string{},
+			expectedInfoAnnotations:    []string{},
+		},
+		"no info annotations when no samples due to mixed data types": {
+			data: `
+				series{label="a"} 1 {{schema:1 sum:15 count:10 buckets:[1 2 3]}}
+			`,
+			expr: "rate(series[1m1s])",
+			expectedWarningAnnotations: []string{
+				`PromQL warning: encountered a mix of histograms and floats for metric name "series" (1:6)`,
+			},
+			expectedInfoAnnotations: []string{},
+		},
+		"no info annotations when selecting two native histograms": {
+			data: `
+				series{label="a"} {{schema:1 sum:10 count:5 buckets:[1 2 3]}} {{schema:1 sum:15 count:10 buckets:[1 2 3]}}
+			`,
+			expr:                       "rate(series[1m1s])",
+			expectedWarningAnnotations: []string{},
+			expectedInfoAnnotations:    []string{},
+		},
+	}
+	for name, testCase := range testCases {
+		t.Run(name, func(t *testing.T) {
+			store := promqltest.LoadedStorage(t, "load 1m\n"+strings.TrimSpace(testCase.data))
+			t.Cleanup(func() { _ = store.Close() })
+
+			engine := newTestEngine(t)
+			query, err := engine.NewInstantQuery(context.Background(), store, nil, testCase.expr, timestamp.Time(0).Add(1*time.Minute))
+			require.NoError(t, err)
+			t.Cleanup(query.Close)
+
+			res := query.Exec(context.Background())
+			require.NoError(t, res.Err)
+
+			warnings, infos := res.Warnings.AsStrings(testCase.expr, 0, 0)
+			testutil.RequireEqual(t, testCase.expectedWarningAnnotations, warnings)
+			testutil.RequireEqual(t, testCase.expectedInfoAnnotations, infos)
+		})
+	}
+}