Alerting: Fix provisioning of contact points when contact point is renamed (#74238)

* add test that demonstrates the bug
* fix renaming provisioning contact points when it is the last in the group

pkg/services/ngalert/provisioning/contactpoints.go

@@ -454,7 +454,7 @@ func stitchReceiver(cfg *apimodels.PostableUserConfig, target *apimodels.Postabl
 	// All receivers in a given receiver group have the same name. We must maintain this across renames.
 	configModified := false
 groupLoop:
-	for _, receiverGroup := range cfg.AlertmanagerConfig.Receivers {
+	for groupIdx, receiverGroup := range cfg.AlertmanagerConfig.Receivers {
 		// Does the current group contain the grafana receiver we're interested in?
 		for i, grafanaReceiver := range receiverGroup.GrafanaManagedReceivers {
 			if grafanaReceiver.UID == target.UID {
@@ -477,8 +477,6 @@ groupLoop:
 					replaceReferences(receiverGroup.Name, target.Name, cfg.AlertmanagerConfig.Route)
 					receiverGroup.Name = target.Name
 					receiverGroup.GrafanaManagedReceivers[i] = target
-					configModified = true
-					break groupLoop
 				}
 
 				// Otherwise, we only want to rename the receiver we are touching... NOT all of them.
@@ -491,6 +489,11 @@ groupLoop:
 						// Add the modified receiver to the new group...
 						candidateExistingGroup.GrafanaManagedReceivers = append(candidateExistingGroup.GrafanaManagedReceivers, target)
 						configModified = true
+
+						// if the old receiver group turns out to be empty. Remove it.
+						if len(receiverGroup.GrafanaManagedReceivers) == 0 {
+							cfg.AlertmanagerConfig.Receivers = append(cfg.AlertmanagerConfig.Receivers[:groupIdx], cfg.AlertmanagerConfig.Receivers[groupIdx+1:]...)
+						}
 						break groupLoop
 					}
 				}

pkg/services/ngalert/provisioning/contactpoints_test.go

@@ -992,6 +992,108 @@ func TestStitchReceivers(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "single item group rename to existing group",
+			initial: &definitions.PostableUserConfig{
+				AlertmanagerConfig: definitions.PostableApiAlertingConfig{
+					Config: definitions.Config{
+						Route: &definitions.Route{
+							Receiver: "receiver-1",
+							Routes: []*definitions.Route{
+								{
+									Receiver: "receiver-1",
+								},
+								{
+									Receiver: "receiver-2",
+								},
+							},
+						},
+					},
+					Receivers: []*definitions.PostableApiReceiver{
+						{
+							Receiver: config.Receiver{
+								Name: "receiver-1",
+							},
+							PostableGrafanaReceivers: definitions.PostableGrafanaReceivers{
+								GrafanaManagedReceivers: []*definitions.PostableGrafanaReceiver{
+									{
+										UID:  "1",
+										Name: "receiver-1",
+										Type: "slack",
+									},
+									{
+										UID:  "2",
+										Name: "receiver-1",
+										Type: "slack",
+									},
+								},
+							},
+						},
+						{
+							Receiver: config.Receiver{
+								Name: "receiver-2",
+							},
+							PostableGrafanaReceivers: definitions.PostableGrafanaReceivers{
+								GrafanaManagedReceivers: []*definitions.PostableGrafanaReceiver{
+									{
+										UID:  "3",
+										Name: "receiver-2",
+										Type: "slack",
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			new: &definitions.PostableGrafanaReceiver{
+				UID:  "3",
+				Name: "receiver-1",
+				Type: "slack",
+			},
+			expModified: true,
+			expCfg: definitions.PostableApiAlertingConfig{
+				Config: definitions.Config{
+					Route: &definitions.Route{
+						Receiver: "receiver-1",
+						Routes: []*definitions.Route{
+							{
+								Receiver: "receiver-1",
+							},
+							{
+								Receiver: "receiver-1",
+							},
+						},
+					},
+				},
+				Receivers: []*definitions.PostableApiReceiver{
+					{
+						Receiver: config.Receiver{
+							Name: "receiver-1",
+						},
+						PostableGrafanaReceivers: definitions.PostableGrafanaReceivers{
+							GrafanaManagedReceivers: []*definitions.PostableGrafanaReceiver{
+								{
+									UID:  "1",
+									Name: "receiver-1",
+									Type: "slack",
+								},
+								{
+									UID:  "2",
+									Name: "receiver-1",
+									Type: "slack",
+								},
+								{
+									UID:  "3",
+									Name: "receiver-1",
+									Type: "slack",
+								},
+							},
+						},
+					},
+				},
+			},
+		},
 	}
 
 	for _, c := range cases {