Cherry pick 0.32.3

api/v2/compat.go

@@ -38,6 +38,7 @@ func GettableSilenceFromProto(s *silencepb.Silence) (open_api_models.GettableSil
 		Silence: open_api_models.Silence{
 			StartsAt:    &start,
 			EndsAt:      &end,
+			Matchers:    open_api_models.Matchers{},
 			Comment:     &s.Comment,
 			CreatedBy:   &s.CreatedBy,
 			Annotations: s.Annotations,

docs/configuration.md

@@ -1895,6 +1895,7 @@ endpoint:
   "commonLabels": <object>,
   "commonAnnotations": <object>,
   "externalURL": <string>,           // backlink to the Alertmanager.
+  "notification_reason": <string>,   // string represent the reason this notification was generated
   "alerts": [
     {
       "status": "<resolved|firing>",

silence/silence.go

@@ -1321,9 +1321,11 @@ func (s state) MarshalBinary() ([]byte, error) {
 	var buf bytes.Buffer
 
 	for _, e := range s {
-		if _, err := protodelim.MarshalTo(&buf, e); err != nil {
+		b, err := marshalMeshSilence(e)
+		if err != nil {
 			return nil, err
 		}
+		buf.Write(b)
 	}
 	return buf.Bytes(), nil
 }
@@ -1354,7 +1356,9 @@ func decodeState(r io.Reader) (state, error) {
 // the first matcher set to the matchers field for backward compatibility with
 // older alertmanager versions.
 func prepareSilenceForMarshalling(sil *pb.Silence) {
-	if len(sil.MatcherSets) > 0 {
+	// The nil check is here because of rare cases where this function
+	// is called on a nil silence. It's up to the caller to decide if it's a bug
+	if sil != nil && len(sil.MatcherSets) > 0 {
 		sil.Matchers = sil.MatcherSets[0].Matchers
 	}
 }

silence/state_test.go

@@ -13,10 +13,17 @@
 package silence
 
 import (
+	"bufio"
+	"bytes"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/encoding/protodelim"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	pb "github.com/prometheus/alertmanager/silence/silencepb"
 )
 
 func TestCurrentState(t *testing.T) {
@@ -37,3 +44,44 @@ func TestCurrentState(t *testing.T) {
 	expected = CurrentState(pastStartTime, pastEndTime)
 	require.Equal(t, SilenceStateExpired, expected)
 }
+
+// TestStateMarshalBinaryPopulatesLegacyMatchers asserts that snapshots and
+// cluster local-state payloads written by state.MarshalBinary include the
+// deprecated Silence.Matchers field, so that older Alertmanagers that don't
+// understand MatcherSets still see the silence's first matcher set.
+func TestStateMarshalBinaryPopulatesLegacyMatchers(t *testing.T) {
+	now := time.Now()
+	matchers := []*pb.Matcher{
+		{Name: "alertname", Pattern: "Foo", Type: pb.Matcher_EQUAL},
+		{Name: "severity", Pattern: "warn|crit", Type: pb.Matcher_REGEXP},
+	}
+	sil := &pb.Silence{
+		Id:          "abc",
+		MatcherSets: []*pb.MatcherSet{{Matchers: matchers}},
+		StartsAt:    timestamppb.New(now),
+		EndsAt:      timestamppb.New(now.Add(time.Hour)),
+	}
+	st := state{sil.Id: &pb.MeshSilence{
+		Silence:   sil,
+		ExpiresAt: timestamppb.New(now.Add(2 * time.Hour)),
+	}}
+
+	b, err := st.MarshalBinary()
+	require.NoError(t, err)
+
+	require.Nil(t, sil.Matchers, "MarshalBinary must not mutate in-memory silences")
+
+	// Decode directly via protodelim, bypassing decodeState — decodeState
+	// strips the legacy field, but we want to observe the on-the-wire shape.
+	var got pb.MeshSilence
+	require.NoError(t, protodelim.UnmarshalFrom(bufio.NewReader(bytes.NewReader(b)), &got))
+
+	require.Len(t, got.Silence.MatcherSets, 1)
+	require.Len(t, got.Silence.Matchers, len(matchers))
+	for i, m := range matchers {
+		require.True(t, proto.Equal(m, got.Silence.Matchers[i]),
+			"legacy Matchers[%d] mismatch", i)
+		require.True(t, proto.Equal(m, got.Silence.MatcherSets[0].Matchers[i]),
+			"MatcherSets[0].Matchers[%d] mismatch", i)
+	}
+}