PLT-4378 Slack import when channel name is deleted (#4649)

This fixes the issue where the channel fails to Import from Slack if
there is already a channel with the same name on Mattermost that has
been deleted.

app/slackimport.go

@@ -470,18 +470,28 @@ func SlackAddChannels(teamId string, slackchannels []SlackChannel, posts map[str
 			Header:      sChannel.Topic["value"],
 		}
 		newChannel = SlackSanitiseChannelProperties(newChannel)
-		mChannel := ImportChannel(&newChannel)
+
+		var mChannel *model.Channel
+		if result := <-Srv.Store.Channel().GetByName(teamId, sChannel.Name); result.Err == nil {
+			// The channel already exists as an active channel. Merge with the existing one.
+			mChannel = result.Data.(*model.Channel)
+			log.WriteString(utils.T("api.slackimport.slack_add_channels.merge", map[string]interface{}{"DisplayName": newChannel.DisplayName}))
+		} else if result := <-Srv.Store.Channel().GetDeletedByName(teamId, sChannel.Name); result.Err == nil {
+			// The channel already exists but has been deleted. Generate a random string for the handle instead.
+			newChannel.Name = model.NewId()
+			newChannel = SlackSanitiseChannelProperties(newChannel)
+		}
+
+		if mChannel == nil {
+			// Haven't found an existing channel to merge with. Try importing it as a new one.
+			mChannel = ImportChannel(&newChannel)
 			if mChannel == nil {
-			// Maybe it already exists?
-			if result := <-Srv.Store.Channel().GetByName(teamId, sChannel.Name); result.Err != nil {
 				l4g.Warn(utils.T("api.slackimport.slack_add_channels.import_failed.warn"), newChannel.DisplayName)
 				log.WriteString(utils.T("api.slackimport.slack_add_channels.import_failed", map[string]interface{}{"DisplayName": newChannel.DisplayName}))
 				continue
-			} else {
-				mChannel = result.Data.(*model.Channel)
-				log.WriteString(utils.T("api.slackimport.slack_add_channels.merge", map[string]interface{}{"DisplayName": newChannel.DisplayName}))
 			}
 		}
+
 		addSlackUsersToChannel(sChannel.Members, users, mChannel, log)
 		log.WriteString(newChannel.DisplayName + "\r\n")
 		addedChannels[sChannel.Id] = mChannel

i18n/en.json

@@ -4315,6 +4315,14 @@
     "id": "store.sql_channel.get_channels.not_found.app_error",
     "translation": "No channels were found"
   },
+  {
+    "id": "store.sql_channel.get_deleted_by_name.existing.app_error",
+    "translation": "We couldn't find the existing deleted channel"
+  },
+  {
+    "id": "store.sql_channel.get_deleted_by_name.missing.app_error",
+    "translation": "No deleted channel exists with that name"
+  },
   {
     "id": "store.sql_channel.get_extra_members.app_error",
     "translation": "We couldn't get the extra info for channel members"

store/sql_channel_store.go

@@ -579,6 +579,31 @@ func (s SqlChannelStore) getByName(teamId string, name string, includeDeleted bo
 	return storeChannel
 }
 
+func (s SqlChannelStore) GetDeletedByName(teamId string, name string) StoreChannel {
+	storeChannel := make(StoreChannel, 1)
+
+	go func() {
+		result := StoreResult{}
+
+		channel := model.Channel{}
+
+		if err := s.GetReplica().SelectOne(&channel, "SELECT * FROM Channels WHERE (TeamId = :TeamId OR TeamId = '') AND Name = :Name AND DeleteAt != 0", map[string]interface{}{"TeamId": teamId, "Name": name}); err != nil {
+			if err == sql.ErrNoRows {
+				result.Err = model.NewLocAppError("SqlChannelStore.GetDeletedByName", "store.sql_channel.get_deleted_by_name.missing.app_error", nil, "teamId="+teamId+", "+"name="+name+", "+err.Error())
+			} else {
+				result.Err = model.NewLocAppError("SqlChannelStore.GetDeletedByName", "store.sql_channel.get_deleted_by_name.existing.app_error", nil, "teamId="+teamId+", "+"name="+name+", "+err.Error())
+			}
+		} else {
+			result.Data = &channel
+		}
+
+		storeChannel <- result
+		close(storeChannel)
+	}()
+
+	return storeChannel
+}
+
 func (s SqlChannelStore) SaveMember(member *model.ChannelMember) StoreChannel {
 	storeChannel := make(StoreChannel, 1)
 

store/sql_channel_store_test.go

@@ -352,7 +352,8 @@ func TestChannelStoreGetByName(t *testing.T) {
 	o1.Type = model.CHANNEL_OPEN
 	Must(store.Channel().Save(&o1))
 
-	if r1 := <-store.Channel().GetByName(o1.TeamId, o1.Name); r1.Err != nil {
+	r1 := <-store.Channel().GetByName(o1.TeamId, o1.Name)
+	if r1.Err != nil {
 		t.Fatal(r1.Err)
 	} else {
 		if r1.Data.(*model.Channel).ToJson() != o1.ToJson() {
@@ -363,6 +364,36 @@ func TestChannelStoreGetByName(t *testing.T) {
 	if err := (<-store.Channel().GetByName(o1.TeamId, "")).Err; err == nil {
 		t.Fatal("Missing id should have failed")
 	}
+
+	Must(store.Channel().Delete(r1.Data.(*model.Channel).Id, model.GetMillis()))
+
+	if err := (<-store.Channel().GetByName(o1.TeamId, "")).Err; err == nil {
+		t.Fatal("Deleted channel should not be returned by GetByName()")
+	}
+}
+
+func TestChannelStoreGetDeletedByName(t *testing.T) {
+	Setup()
+
+	o1 := model.Channel{}
+	o1.TeamId = model.NewId()
+	o1.DisplayName = "Name"
+	o1.Name = "a" + model.NewId() + "b"
+	o1.Type = model.CHANNEL_OPEN
+	o1.DeleteAt = model.GetMillis()
+	Must(store.Channel().Save(&o1))
+
+	if r1 := <-store.Channel().GetDeletedByName(o1.TeamId, o1.Name); r1.Err != nil {
+		t.Fatal(r1.Err)
+	} else {
+		if r1.Data.(*model.Channel).ToJson() != o1.ToJson() {
+			t.Fatal("invalid returned channel")
+		}
+	}
+
+	if err := (<-store.Channel().GetDeletedByName(o1.TeamId, "")).Err; err == nil {
+		t.Fatal("Missing id should have failed")
+	}
 }
 
 func TestChannelMemberStore(t *testing.T) {

store/store.go

@@ -93,6 +93,7 @@ type ChannelStore interface {
 	PermanentDeleteByTeam(teamId string) StoreChannel
 	GetByName(team_id string, name string) StoreChannel
 	GetByNameIncludeDeleted(team_id string, name string) StoreChannel
+	GetDeletedByName(team_id string, name string) StoreChannel
 	GetChannels(teamId string, userId string) StoreChannel
 	GetMoreChannels(teamId string, userId string, offset int, limit int) StoreChannel
 	GetChannelCounts(teamId string, userId string) StoreChannel