Update channel patch to post the correct system messages (#6290)

api4/channel.go

@@ -170,7 +170,7 @@ func patchChannel(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if rchannel, err := app.PatchChannel(oldChannel, patch); err != nil {
+	if rchannel, err := app.PatchChannel(oldChannel, patch, c.Session.UserId); err != nil {
 		c.Err = err
 		return
 	} else {

app/channel.go

@@ -281,9 +281,36 @@ func UpdateChannel(channel *model.Channel) (*model.Channel, *model.AppError) {
 	}
 }
 
-func PatchChannel(channel *model.Channel, patch *model.ChannelPatch) (*model.Channel, *model.AppError) {
+func PatchChannel(channel *model.Channel, patch *model.ChannelPatch, userId string) (*model.Channel, *model.AppError) {
+	oldChannelDisplayName := channel.DisplayName
+	oldChannelHeader := channel.Header
+	oldChannelPurpose := channel.Purpose
+
 	channel.Patch(patch)
-	return UpdateChannel(channel)
+	channel, err := UpdateChannel(channel)
+	if err != nil {
+		return nil, err
+	}
+
+	if oldChannelDisplayName != channel.DisplayName {
+		if err := PostUpdateChannelDisplayNameMessage(userId, channel.Id, channel.TeamId, oldChannelDisplayName, channel.DisplayName); err != nil {
+			l4g.Error(err.Error())
+		}
+	}
+
+	if channel.Header != oldChannelHeader {
+		if err := PostUpdateChannelHeaderMessage(userId, channel.Id, channel.TeamId, oldChannelHeader, channel.Header); err != nil {
+			l4g.Error(err.Error())
+		}
+	}
+
+	if channel.Purpose != oldChannelPurpose {
+		if err := PostUpdateChannelPurposeMessage(userId, channel.Id, channel.TeamId, oldChannelPurpose, channel.Purpose); err != nil {
+			l4g.Error(err.Error())
+		}
+	}
+
+	return channel, err
 }
 
 func UpdateChannelMemberRoles(channelId string, userId string, newRoles string) (*model.ChannelMember, *model.AppError) {