MM-34549 shared channels; add users to channel that were already sync'd (#17361)

Fixes a bug and adds a feature for shared channels:
- The Bug: when creating new shared channels, users that had already been sync'd via another channel were not added to the new channel's member list, since the users were not sync'd again. This PR sync's users per channel.
- The Feature: support custom statuses

app/app_iface.go

@@ -832,6 +832,7 @@ type AppIface interface {
 	Notification() einterfaces.NotificationInterface
 	NotificationsLog() *mlog.Logger
 	NotifyAndSetWarnMetricAck(warnMetricId string, sender *model.User, forceAck bool, isBot bool) *model.AppError
+	NotifySharedChannelUserUpdate(user *model.User)
 	OpenInteractiveDialog(request model.OpenDialogRequest) *model.AppError
 	OriginChecker() func(*http.Request) bool
 	PatchChannel(channel *model.Channel, patch *model.ChannelPatch, userID string) (*model.Channel, *model.AppError)

app/opentracing/opentracing_layer.go

@@ -11401,6 +11401,21 @@ func (a *OpenTracingAppLayer) NotifySessionsExpired() *model.AppError {
 	return resultVar0
 }
 
+func (a *OpenTracingAppLayer) NotifySharedChannelUserUpdate(user *model.User) {
+	origCtx := a.ctx
+	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.NotifySharedChannelUserUpdate")
+
+	a.ctx = newCtx
+	a.app.Srv().Store.SetContext(newCtx)
+	defer func() {
+		a.app.Srv().Store.SetContext(origCtx)
+		a.ctx = origCtx
+	}()
+
+	defer span.Finish()
+	a.app.NotifySharedChannelUserUpdate(user)
+}
+
 func (a *OpenTracingAppLayer) OpenInteractiveDialog(request model.OpenDialogRequest) *model.AppError {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.OpenInteractiveDialog")

app/shared_channel.go

@@ -147,3 +147,9 @@ func (a *App) GetSharedChannelRemotesStatus(channelID string) ([]*model.SharedCh
 	}
 	return a.Srv().Store.SharedChannel().GetRemotesStatus(channelID)
 }
+
+// SharedChannelUsers
+
+func (a *App) NotifySharedChannelUserUpdate(user *model.User) {
+	a.sendUpdatedUserEvent(*user)
+}

app/slashcommands/command_remote.go

@@ -116,7 +116,11 @@ func (rp *RemoteProvider) doInvite(a *app.App, args *model.CommandArgs, margs ma
 	if name == "" {
 		return responsef(args.T("api.command_remote.missing_empty", map[string]interface{}{"Arg": "name"}))
 	}
+
 	displayname := margs["displayname"]
+	if displayname == "" {
+		displayname = name
+	}
 
 	url := a.GetSiteURL()
 	if url == "" {
@@ -163,7 +167,11 @@ func (rp *RemoteProvider) doAccept(a *app.App, args *model.CommandArgs, margs ma
 	if name == "" {
 		return responsef(args.T("api.command_remote.missing_empty", map[string]interface{}{"Arg": "name"}))
 	}
+
 	displayname := margs["displayname"]
+	if displayname == "" {
+		displayname = name
+	}
 
 	blob := margs["invite"]
 	if blob == "" {