MM-31062: Rewrite empty string checks to be more idiomatic (#16587)

https://mattermost.atlassian.net/browse/MM-31062

```release-note
NONE
```

api4/channel.go

@@ -1447,7 +1447,7 @@ func addChannelMember(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	postRootId, ok := props["post_root_id"].(string)
-	if ok && len(postRootId) != 0 && !model.IsValidId(postRootId) {
+	if ok && postRootId != "" && !model.IsValidId(postRootId) {
 		c.SetInvalidParam("post_root_id")
 		return
 	}

api4/config_test.go

@@ -29,18 +29,18 @@ func TestGetConfig(t *testing.T) {
 
 		require.NotEqual(t, "", cfg.TeamSettings.SiteName)
 
-		if *cfg.LdapSettings.BindPassword != model.FAKE_SETTING && len(*cfg.LdapSettings.BindPassword) != 0 {
+		if *cfg.LdapSettings.BindPassword != model.FAKE_SETTING && *cfg.LdapSettings.BindPassword != "" {
 			require.FailNow(t, "did not sanitize properly")
 		}
 		require.Equal(t, model.FAKE_SETTING, *cfg.FileSettings.PublicLinkSalt, "did not sanitize properly")
 
-		if *cfg.FileSettings.AmazonS3SecretAccessKey != model.FAKE_SETTING && len(*cfg.FileSettings.AmazonS3SecretAccessKey) != 0 {
+		if *cfg.FileSettings.AmazonS3SecretAccessKey != model.FAKE_SETTING && *cfg.FileSettings.AmazonS3SecretAccessKey != "" {
 			require.FailNow(t, "did not sanitize properly")
 		}
-		if *cfg.EmailSettings.SMTPPassword != model.FAKE_SETTING && len(*cfg.EmailSettings.SMTPPassword) != 0 {
+		if *cfg.EmailSettings.SMTPPassword != model.FAKE_SETTING && *cfg.EmailSettings.SMTPPassword != "" {
 			require.FailNow(t, "did not sanitize properly")
 		}
-		if *cfg.GitLabSettings.Secret != model.FAKE_SETTING && len(*cfg.GitLabSettings.Secret) != 0 {
+		if *cfg.GitLabSettings.Secret != model.FAKE_SETTING && *cfg.GitLabSettings.Secret != "" {
 			require.FailNow(t, "did not sanitize properly")
 		}
 		require.Equal(t, model.FAKE_SETTING, *cfg.SqlSettings.DataSource, "did not sanitize properly")

api4/user.go

@@ -559,7 +559,7 @@ func getFilteredUsersStats(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 	}
 	channelRoles := []string{}
-	if channelRolesString != "" && len(channelID) != 0 {
+	if channelRolesString != "" && channelID != "" {
 		channelRoles, rolesValid = model.CleanRoleNames(strings.Split(channelRolesString, ","))
 		if !rolesValid {
 			c.SetInvalidParam("channelRoles")
@@ -567,7 +567,7 @@ func getFilteredUsersStats(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 	}
 	teamRoles := []string{}
-	if teamRolesString != "" && len(teamID) != 0 {
+	if teamRolesString != "" && teamID != "" {
 		teamRoles, rolesValid = model.CleanRoleNames(strings.Split(teamRolesString, ","))
 		if !rolesValid {
 			c.SetInvalidParam("teamRoles")
@@ -673,7 +673,7 @@ func getUsers(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 	}
 	channelRoles := []string{}
-	if channelRolesString != "" && len(inChannelId) != 0 {
+	if channelRolesString != "" && inChannelId != "" {
 		channelRoles, rolesValid = model.CleanRoleNames(strings.Split(channelRolesString, ","))
 		if !rolesValid {
 			c.SetInvalidParam("channelRoles")
@@ -681,7 +681,7 @@ func getUsers(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 	}
 	teamRoles := []string{}
-	if teamRolesString != "" && len(inTeamId) != 0 {
+	if teamRolesString != "" && inTeamId != "" {
 		teamRoles, rolesValid = model.CleanRoleNames(strings.Split(teamRolesString, ","))
 		if !rolesValid {
 			c.SetInvalidParam("teamRoles")

app/channel.go

@@ -629,7 +629,7 @@ func (a *App) CreateChannelScheme(channel *model.Channel) (*model.Scheme, *model
 
 // DeleteChannelScheme deletes a channels scheme and sets its SchemeId to nil.
 func (a *App) DeleteChannelScheme(channel *model.Channel) (*model.Channel, *model.AppError) {
-	if channel.SchemeId != nil && len(*channel.SchemeId) != 0 {
+	if channel.SchemeId != nil && *channel.SchemeId != "" {
 		if _, err := a.DeleteScheme(*channel.SchemeId); err != nil {
 			return nil, err
 		}
@@ -784,7 +784,7 @@ func (a *App) GetSchemeRolesForChannel(channelId string) (guestRoleName, userRol
 		return
 	}
 
-	if channel.SchemeId != nil && len(*channel.SchemeId) != 0 {
+	if channel.SchemeId != nil && *channel.SchemeId != "" {
 		var scheme *model.Scheme
 		scheme, err = a.GetScheme(*channel.SchemeId)
 		if err != nil {
@@ -808,7 +808,7 @@ func (a *App) GetTeamSchemeChannelRoles(teamId string) (guestRoleName, userRoleN
 		return
 	}
 
-	if team.SchemeId != nil && len(*team.SchemeId) != 0 {
+	if team.SchemeId != nil && *team.SchemeId != "" {
 		var scheme *model.Scheme
 		scheme, err = a.GetScheme(*team.SchemeId)
 		if err != nil {

app/command.go

@@ -520,7 +520,7 @@ func (a *App) DoCommandRequest(cmd *model.Command, p url.Values) (*model.Command
 
 func (a *App) HandleCommandResponse(command *model.Command, args *model.CommandArgs, response *model.CommandResponse, builtIn bool) (*model.CommandResponse, *model.AppError) {
 	trigger := ""
-	if len(args.Command) != 0 {
+	if args.Command != "" {
 		parts := strings.Split(args.Command, " ")
 		trigger = parts[0][1:]
 		trigger = strings.ToLower(trigger)
@@ -561,7 +561,7 @@ func (a *App) HandleCommandResponsePost(command *model.Command, args *model.Comm
 	post.Type = response.Type
 	post.SetProps(response.Props)
 
-	if len(response.ChannelId) != 0 {
+	if response.ChannelId != "" {
 		_, err := a.GetChannelMember(response.ChannelId, args.UserId)
 		if err != nil {
 			err = model.NewAppError("HandleCommandResponsePost", "api.command.command_post.forbidden.app_error", nil, err.Error(), http.StatusForbidden)
@@ -573,20 +573,20 @@ func (a *App) HandleCommandResponsePost(command *model.Command, args *model.Comm
 	isBotPost := !builtIn
 
 	if *a.Config().ServiceSettings.EnablePostUsernameOverride {
-		if len(command.Username) != 0 {
+		if command.Username != "" {
 			post.AddProp("override_username", command.Username)
 			isBotPost = true
-		} else if len(response.Username) != 0 {
+		} else if response.Username != "" {
 			post.AddProp("override_username", response.Username)
 			isBotPost = true
 		}
 	}
 
 	if *a.Config().ServiceSettings.EnablePostIconOverride {
-		if len(command.IconURL) != 0 {
+		if command.IconURL != "" {
 			post.AddProp("override_icon_url", command.IconURL)
 			isBotPost = true
-		} else if len(response.IconURL) != 0 {
+		} else if response.IconURL != "" {
 			post.AddProp("override_icon_url", response.IconURL)
 			isBotPost = true
 		} else {

app/login.go

@@ -122,7 +122,7 @@ func (a *App) GetUserForLogin(id, loginId string) (*model.User, *model.AppError)
 	enableEmail := *a.Config().EmailSettings.EnableSignInWithEmail
 
 	// If we are given a userID then fail if we can't find a user with that ID
-	if len(id) != 0 {
+	if id != "" {
 		user, err := a.GetUser(id)
 		if err != nil {
 			if err.Id != MISSING_ACCOUNT_ERROR {

app/notification.go

@@ -780,10 +780,10 @@ func getMentionsEnabledFields(post *model.Post) model.StringArray {
 	ret = append(ret, post.Message)
 	for _, attachment := range post.Attachments() {
 
-		if len(attachment.Pretext) != 0 {
+		if attachment.Pretext != "" {
 			ret = append(ret, attachment.Pretext)
 		}
-		if len(attachment.Text) != 0 {
+		if attachment.Text != "" {
 			ret = append(ret, attachment.Text)
 		}
 	}

app/notification_email.go

@@ -314,7 +314,7 @@ func (a *App) generateHyperlinkForChannels(postMessage, teamName, teamURL string
 }
 
 func (s *Server) GetMessageForNotification(post *model.Post, translateFunc i18n.TranslateFunc) string {
-	if len(strings.TrimSpace(post.Message)) != 0 || len(post.FileIds) == 0 {
+	if strings.TrimSpace(post.Message) != "" || len(post.FileIds) == 0 {
 		return post.Message
 	}
 

app/oauth.go

@@ -415,11 +415,11 @@ func (a *App) newSessionUpdateToken(appName string, accessData *model.AccessData
 func (a *App) GetOAuthLoginEndpoint(w http.ResponseWriter, r *http.Request, service, teamId, action, redirectTo, loginHint string, isMobile bool) (string, *model.AppError) {
 	stateProps := map[string]string{}
 	stateProps["action"] = action
-	if len(teamId) != 0 {
+	if teamId != "" {
 		stateProps["team_id"] = teamId
 	}
 
-	if len(redirectTo) != 0 {
+	if redirectTo != "" {
 		stateProps["redirect_to"] = redirectTo
 	}
 
@@ -436,7 +436,7 @@ func (a *App) GetOAuthLoginEndpoint(w http.ResponseWriter, r *http.Request, serv
 func (a *App) GetOAuthSignupEndpoint(w http.ResponseWriter, r *http.Request, service, teamId string) (string, *model.AppError) {
 	stateProps := map[string]string{}
 	stateProps["action"] = model.OAUTH_ACTION_SIGNUP
-	if len(teamId) != 0 {
+	if teamId != "" {
 		stateProps["team_id"] = teamId
 	}
 

app/team.go

@@ -342,7 +342,7 @@ func (a *App) GetSchemeRolesForTeam(teamId string) (string, string, string, *mod
 		return "", "", "", err
 	}
 
-	if team.SchemeId != nil && len(*team.SchemeId) != 0 {
+	if team.SchemeId != nil && *team.SchemeId != "" {
 		scheme, err := a.GetScheme(*team.SchemeId)
 		if err != nil {
 			return "", "", "", err

app/user.go

@@ -1497,7 +1497,7 @@ func (a *App) SendPasswordReset(email string, siteURL string) (bool, *model.AppE
 		return false, nil
 	}
 
-	if user.AuthData != nil && len(*user.AuthData) != 0 {
+	if user.AuthData != nil && *user.AuthData != "" {
 		return false, model.NewAppError("SendPasswordReset", "api.user.send_password_reset.sso.app_error", nil, "userId="+user.Id, http.StatusBadRequest)
 	}
 

app/webhook.go

@@ -264,7 +264,7 @@ func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, ove
 	}
 
 	if *a.Config().ServiceSettings.EnablePostUsernameOverride {
-		if len(overrideUsername) != 0 {
+		if overrideUsername != "" {
 			post.AddProp("override_username", overrideUsername)
 		} else {
 			post.AddProp("override_username", model.DEFAULT_WEBHOOK_USERNAME)
@@ -272,10 +272,10 @@ func (a *App) CreateWebhookPost(userId string, channel *model.Channel, text, ove
 	}
 
 	if *a.Config().ServiceSettings.EnablePostIconOverride {
-		if len(overrideIconUrl) != 0 {
+		if overrideIconUrl != "" {
 			post.AddProp("override_icon_url", overrideIconUrl)
 		}
-		if len(overrideIconEmoji) != 0 {
+		if overrideIconEmoji != "" {
 			post.AddProp("override_icon_emoji", overrideIconEmoji)
 		}
 	}
@@ -445,7 +445,7 @@ func (a *App) CreateOutgoingWebhook(hook *model.OutgoingWebhook) (*model.Outgoin
 		return nil, model.NewAppError("CreateOutgoingWebhook", "api.outgoing_webhook.disabled.app_error", nil, "", http.StatusNotImplemented)
 	}
 
-	if len(hook.ChannelId) != 0 {
+	if hook.ChannelId != "" {
 		channel, errCh := a.Srv().Store.Channel().Get(hook.ChannelId, true)
 		if errCh != nil {
 			var nfErr *store.ErrNotFound
@@ -696,7 +696,7 @@ func (a *App) HandleIncomingWebhook(hookId string, req *model.IncomingWebhookReq
 	var channel *model.Channel
 	var cchan chan store.StoreResult
 
-	if len(channelName) != 0 {
+	if channelName != "" {
 		if channelName[0] == '@' {
 			result, nErr := a.Srv().Store.User().GetByUsername(channelName[1:])
 			if nErr != nil {

model/command_webhook.go

@@ -53,11 +53,11 @@ func (o *CommandWebhook) IsValid() *AppError {
 		return NewAppError("CommandWebhook.IsValid", "model.command_hook.channel_id.app_error", nil, "", http.StatusBadRequest)
 	}
 
-	if len(o.RootId) != 0 && !IsValidId(o.RootId) {
+	if o.RootId != "" && !IsValidId(o.RootId) {
 		return NewAppError("CommandWebhook.IsValid", "model.command_hook.root_id.app_error", nil, "", http.StatusBadRequest)
 	}
 
-	if len(o.ParentId) != 0 && !IsValidId(o.ParentId) {
+	if o.ParentId != "" && !IsValidId(o.ParentId) {
 		return NewAppError("CommandWebhook.IsValid", "model.command_hook.parent_id.app_error", nil, "", http.StatusBadRequest)
 	}
 

model/config.go

@@ -3484,13 +3484,13 @@ func (s *ServiceSettings) isValid() *AppError {
 		return NewAppError("Config.IsValid", "model.config.is_valid.login_attempts.app_error", nil, "", http.StatusBadRequest)
 	}
 
-	if len(*s.SiteURL) != 0 {
+	if *s.SiteURL != "" {
 		if _, err := url.ParseRequestURI(*s.SiteURL); err != nil {
 			return NewAppError("Config.IsValid", "model.config.is_valid.site_url.app_error", nil, "", http.StatusBadRequest)
 		}
 	}
 
-	if len(*s.WebsocketURL) != 0 {
+	if *s.WebsocketURL != "" {
 		if _, err := url.ParseRequestURI(*s.WebsocketURL); err != nil {
 			return NewAppError("Config.IsValid", "model.config.is_valid.websocket_url.app_error", nil, "", http.StatusBadRequest)
 		}

model/file_info.go

@@ -114,7 +114,7 @@ func (fi *FileInfo) IsValid() *AppError {
 		return NewAppError("FileInfo.IsValid", "model.file_info.is_valid.user_id.app_error", nil, "id="+fi.Id, http.StatusBadRequest)
 	}
 
-	if len(fi.PostId) != 0 && !IsValidId(fi.PostId) {
+	if fi.PostId != "" && !IsValidId(fi.PostId) {
 		return NewAppError("FileInfo.IsValid", "model.file_info.is_valid.post_id.app_error", nil, "id="+fi.Id, http.StatusBadRequest)
 	}
 

model/outgoing_webhook.go

@@ -140,7 +140,7 @@ func (o *OutgoingWebhook) IsValid() *AppError {
 		return NewAppError("OutgoingWebhook.IsValid", "model.outgoing_hook.is_valid.user_id.app_error", nil, "", http.StatusBadRequest)
 	}
 
-	if len(o.ChannelId) != 0 && !IsValidId(o.ChannelId) {
+	if o.ChannelId != "" && !IsValidId(o.ChannelId) {
 		return NewAppError("OutgoingWebhook.IsValid", "model.outgoing_hook.is_valid.channel_id.app_error", nil, "", http.StatusBadRequest)
 	}
 

model/scheme.go

@@ -159,15 +159,15 @@ func (scheme *Scheme) IsValidForCreate() bool {
 	}
 
 	if scheme.Scope == SCHEME_SCOPE_CHANNEL {
-		if len(scheme.DefaultTeamAdminRole) != 0 {
+		if scheme.DefaultTeamAdminRole != "" {
 			return false
 		}
 
-		if len(scheme.DefaultTeamUserRole) != 0 {
+		if scheme.DefaultTeamUserRole != "" {
 			return false
 		}
 
-		if len(scheme.DefaultTeamGuestRole) != 0 {
+		if scheme.DefaultTeamGuestRole != "" {
 			return false
 		}
 	}

model/search_params.go

@@ -214,7 +214,7 @@ func parseSearchFlags(input []string) ([]searchWord, []flag) {
 			// and remove extra pound #s
 			word = hashtagStart.ReplaceAllString(word, "#")
 
-			if len(word) != 0 {
+			if word != "" {
 				words = append(words, searchWord{
 					word,
 					exclude,
@@ -345,9 +345,9 @@ func ParseSearchParams(text string, timeZoneOffset int) []*SearchParams {
 		len(excludedPlainTerms) == 0 && len(excludedHashtagTerms) == 0 &&
 		(len(inChannels) != 0 || len(fromUsers) != 0 ||
 			len(excludedChannels) != 0 || len(excludedUsers) != 0 ||
-			len(afterDate) != 0 || len(excludedAfterDate) != 0 ||
-			len(beforeDate) != 0 || len(excludedBeforeDate) != 0 ||
-			len(onDate) != 0 || len(excludedDate) != 0) {
+			afterDate != "" || excludedAfterDate != "" ||
+			beforeDate != "" || excludedBeforeDate != "" ||
+			onDate != "" || excludedDate != "") {
 		paramsList = append(paramsList, &SearchParams{
 			Terms:              "",
 			ExcludedTerms:      "",

store/localcachelayer/role_layer.go

@@ -33,7 +33,7 @@ func (s *LocalCacheRoleStore) handleClusterInvalidateRolePermissions(msg *model.
 }
 
 func (s LocalCacheRoleStore) Save(role *model.Role) (*model.Role, error) {
-	if len(role.Name) != 0 {
+	if role.Name != "" {
 		defer s.rootStore.doInvalidateCacheCluster(s.rootStore.roleCache, role.Name)
 		defer s.rootStore.doClearCacheCluster(s.rootStore.rolePermissionsCache)
 	}

store/localcachelayer/scheme_layer.go

@@ -22,7 +22,7 @@ func (s *LocalCacheSchemeStore) handleClusterInvalidateScheme(msg *model.Cluster
 }
 
 func (s LocalCacheSchemeStore) Save(scheme *model.Scheme) (*model.Scheme, error) {
-	if len(scheme.Id) != 0 {
+	if scheme.Id != "" {
 		defer s.rootStore.doInvalidateCacheCluster(s.rootStore.schemeCache, scheme.Id)
 	}
 	return s.SchemeStore.Save(scheme)

store/sqlstore/audit_store.go

@@ -57,7 +57,7 @@ func (s SqlAuditStore) Get(userId string, offset int, limit int) (model.Audits,
 		Limit(uint64(limit)).
 		Offset(uint64(offset))
 
-	if len(userId) != 0 {
+	if userId != "" {
 		query = query.Where(sq.Eq{"UserId": userId})
 	}
 

store/sqlstore/group_store.go

@@ -91,7 +91,7 @@ func (s *SqlGroupStore) createIndexesIfNotExists() {
 }
 
 func (s *SqlGroupStore) Create(group *model.Group) (*model.Group, error) {
-	if len(group.Id) != 0 {
+	if group.Id != "" {
 		return nil, store.NewErrInvalidInput("Group", "id", group.Id)
 	}
 

store/sqlstore/user_store.go

@@ -286,7 +286,7 @@ func (us SqlUserStore) UpdateAuthData(userId string, service string, authData *s
 			     AuthService = :AuthService,
 			     AuthData = :AuthData`
 
-	if len(email) != 0 {
+	if email != "" {
 		query += ", Email = lower(:Email)"
 	}
 

web/handlers.go

@@ -188,7 +188,7 @@ func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	token, tokenLocation := app.ParseAuthTokenFromRequest(r)
 
-	if len(token) != 0 && tokenLocation != app.TokenLocationCloudHeader {
+	if token != "" && tokenLocation != app.TokenLocationCloudHeader {
 		session, err := c.App.GetSession(token)
 		if err != nil {
 			c.Log.Info("Invalid session", mlog.Err(err))
@@ -210,7 +210,7 @@ func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 
 		h.checkCSRFToken(c, r, token, tokenLocation, session)
-	} else if len(token) != 0 && c.App.Srv().License() != nil && *c.App.Srv().License().Features.Cloud && tokenLocation == app.TokenLocationCloudHeader {
+	} else if token != "" && c.App.Srv().License() != nil && *c.App.Srv().License().Features.Cloud && tokenLocation == app.TokenLocationCloudHeader {
 		// Check to see if this provided token matches our CWS Token
 		session, err := c.App.GetCloudSession(token)
 		if err != nil {

web/saml.go

@@ -38,7 +38,7 @@ func loginWithSaml(c *Context, w http.ResponseWriter, r *http.Request) {
 	relayProps := map[string]string{}
 	relayState := ""
 
-	if len(action) != 0 {
+	if action != "" {
 		relayProps["team_id"] = teamId
 		relayProps["action"] = action
 		if action == model.OAUTH_ACTION_EMAIL_TO_SSO {
@@ -46,7 +46,7 @@ func loginWithSaml(c *Context, w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	if len(redirectTo) != 0 {
+	if redirectTo != "" {
 		relayProps["redirect_to"] = redirectTo
 	}