[v9.0.x] Alerting: Fix Slack push notifications (#52476)

This commit fixes push notifications for Slack which used to show "This content cannot be displayed". The text field is shown in both the message and the push notification.

(cherry picked from commit 094dfd0d4d)

Co-authored-by: George Robinson <george.robinson@grafana.com>

pkg/services/ngalert/notifier/channels/slack.go

@@ -166,6 +166,7 @@ func NewSlackNotifier(config *SlackConfig,
 // slackMessage is the slackMessage for sending a slack notification.
 type slackMessage struct {
 	Channel     string                   `json:"channel,omitempty"`
+	Text        string                   `json:"text,omitempty"`
 	Username    string                   `json:"username,omitempty"`
 	IconEmoji   string                   `json:"icon_emoji,omitempty"`
 	IconURL     string                   `json:"icon_url,omitempty"`
@@ -299,6 +300,7 @@ func (sn *SlackNotifier) buildSlackMessage(ctx context.Context, alrts []*types.A
 
 	req := &slackMessage{
 		Channel:   tmpl(sn.Recipient),
+		Text:      tmpl(sn.Title),
 		Username:  tmpl(sn.Username),
 		IconEmoji: tmpl(sn.IconEmoji),
 		IconURL:   tmpl(sn.IconURL),

pkg/services/ngalert/notifier/channels/slack_test.go

@@ -64,6 +64,7 @@ func TestSlackNotifier(t *testing.T) {
 			},
 			expMsg: &slackMessage{
 				Channel:   "#testchannel",
+				Text:      "[FIRING:1]  (val1)",
 				Username:  "Grafana",
 				IconEmoji: ":emoji:",
 				Attachments: []attachment{
@@ -99,6 +100,7 @@ func TestSlackNotifier(t *testing.T) {
 			},
 			expMsg: &slackMessage{
 				Channel:   "#testchannel",
+				Text:      "[FIRING:1]  (val1)",
 				Username:  "Grafana",
 				IconEmoji: ":emoji:",
 				Attachments: []attachment{
@@ -134,6 +136,7 @@ func TestSlackNotifier(t *testing.T) {
 			},
 			expMsg: &slackMessage{
 				Channel:   "#testchannel",
+				Text:      "[FIRING:1]  (val1)",
 				Username:  "Grafana",
 				IconEmoji: ":emoji:",
 				Attachments: []attachment{
@@ -177,6 +180,7 @@ func TestSlackNotifier(t *testing.T) {
 			},
 			expMsg: &slackMessage{
 				Channel:   "#testchannel",
+				Text:      "2 firing, 0 resolved",
 				Username:  "Grafana",
 				IconEmoji: ":emoji:",
 				Attachments: []attachment{
@@ -225,6 +229,7 @@ func TestSlackNotifier(t *testing.T) {
 			},
 			expMsg: &slackMessage{
 				Channel:   "#testchannel",
+				Text:      "[FIRING:1]  (val1)",
 				Username:  "Grafana",
 				IconEmoji: ":emoji:",
 				Attachments: []attachment{

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -2118,6 +2118,7 @@ var expNonEmailNotifications = map[string][]string{
 	"slack_recv1/slack_test_without_token": {
 		`{
 		  "channel": "#test-channel",
+          "text": "Integration Test [FIRING:1] SlackAlert1 ",
 		  "username": "Integration Test",
 		  "icon_emoji": "🚀",
 		  "icon_url": "https://awesomeemoji.com/rocket",
@@ -2147,6 +2148,7 @@ var expNonEmailNotifications = map[string][]string{
 	"slack_recvX/slack_testX": {
 		`{
 		  "channel": "#test-channel",
+          "text": "[FIRING:1] SlackAlert2 ",
 		  "username": "Integration Test",
 		  "attachments": [
 			{