Alerting: Set "value" with evalmatches in G Managed (#34075)

When, and currently only when using a classic condition, evaluation information is added (which is like the EvalMatches from dashboard alerting).

This is returned via the API and can be included in notifications by reading the `__value__` label attached `.Alerts` in the template. It is a string.

pkg/services/ngalert/eval/eval.go

@@ -63,6 +63,11 @@ type Result struct {
 	Error              error
 	EvaluatedAt        time.Time
 	EvaluationDuration time.Duration
+
+	// EvaluationSring is a string representation of evaluation data such
+	// as EvalMatches (from "classic condition"), and in the future from operations
+	// like SSE "math".
+	EvaluationString string
 }
 
 // State is an enum of the evaluation State for an alert instance.
@@ -265,6 +270,7 @@ func evaluateExecutionResult(execResults ExecutionResults, ts time.Time) Results
 			Instance:           f.Fields[0].Labels,
 			EvaluatedAt:        ts,
 			EvaluationDuration: time.Since(ts),
+			EvaluationString:   extractEvalString(f),
 		}
 
 		switch {

pkg/services/ngalert/eval/extract_md.go

@@ -0,0 +1,46 @@
+package eval
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	"github.com/grafana/grafana/pkg/expr/classic"
+)
+
+func extractEvalString(frame *data.Frame) (s string) {
+	if frame == nil {
+		return "empty frame"
+	}
+
+	if frame.Meta == nil || frame.Meta.Custom == nil {
+		return
+	}
+
+	evalMatches, ok := frame.Meta.Custom.([]classic.EvalMatch)
+	if !ok {
+		return
+	}
+
+	sb := strings.Builder{}
+
+	for i, m := range evalMatches {
+		sb.WriteString("[ ")
+		sb.WriteString(fmt.Sprintf("metric='%s' ", m.Metric))
+		sb.WriteString(fmt.Sprintf("labels={%s} ", m.Labels))
+
+		valString := "null"
+		if m.Value != nil {
+			valString = fmt.Sprintf("%v", *m.Value)
+		}
+
+		sb.WriteString(fmt.Sprintf("value=%v ", valString))
+
+		sb.WriteString("]")
+		if i < len(evalMatches)-1 {
+			sb.WriteString(", ")
+		}
+	}
+
+	return sb.String()
+}

pkg/services/ngalert/eval/extract_md_test.go

@@ -0,0 +1,56 @@
+package eval
+
+import (
+	"testing"
+
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	"github.com/grafana/grafana/pkg/expr/classic"
+	"github.com/stretchr/testify/require"
+	ptr "github.com/xorcare/pointer"
+)
+
+func TestExtractEvalString(t *testing.T) {
+	cases := []struct {
+		desc      string
+		inFrame   *data.Frame
+		outString string
+	}{
+		{
+			desc: "1 EvalMatch",
+			inFrame: newMetaFrame([]classic.EvalMatch{
+				{Metric: "Test", Labels: data.Labels{"host": "foo"}, Value: ptr.Float64(32.3)},
+			}, ptr.Float64(1)),
+			outString: `[ metric='Test' labels={host=foo} value=32.3 ]`,
+		},
+		{
+			desc: "2 EvalMatches",
+			inFrame: newMetaFrame([]classic.EvalMatch{
+				{Metric: "Test", Labels: data.Labels{"host": "foo"}, Value: ptr.Float64(32.3)},
+				{Metric: "Test", Labels: data.Labels{"host": "baz"}, Value: ptr.Float64(10)},
+			}, ptr.Float64(1)),
+			outString: `[ metric='Test' labels={host=foo} value=32.3 ], [ metric='Test' labels={host=baz} value=10 ]`,
+		},
+		{
+			desc: "3 EvalMatches",
+			inFrame: newMetaFrame([]classic.EvalMatch{
+				{Metric: "Test", Labels: data.Labels{"host": "foo"}, Value: ptr.Float64(32.3)},
+				{Metric: "Test", Labels: data.Labels{"host": "baz"}, Value: ptr.Float64(10)},
+				{Metric: "TestA", Labels: data.Labels{"host": "zip"}, Value: ptr.Float64(11)},
+			}, ptr.Float64(1)),
+			outString: `[ metric='Test' labels={host=foo} value=32.3 ], [ metric='Test' labels={host=baz} value=10 ], [ metric='TestA' labels={host=zip} value=11 ]`,
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.desc, func(t *testing.T) {
+			require.Equal(t, tc.outString, extractEvalString(tc.inFrame))
+		})
+	}
+}
+
+func newMetaFrame(custom interface{}, val *float64) *data.Frame {
+	return data.NewFrame("",
+		data.NewField("", nil, []*float64{val})).
+		SetMeta(&data.FrameMeta{
+			Custom: custom,
+		})
+}