Avoid cycle-redirecting user/login page (#28636)

Fix #28231, and remove some unused code. The `db.HasEngine` doesn't seem
useful because the db engine is always initialized before web route.

models/auth/source.go

@@ -261,16 +261,12 @@ func (opts FindSourcesOptions) ToConds() builder.Cond {
 // IsSSPIEnabled returns true if there is at least one activated login
 // source of type LoginSSPI
 func IsSSPIEnabled(ctx context.Context) bool {
-	if !db.HasEngine {
-		return false
-	}
-
 	exist, err := db.Exist[Source](ctx, FindSourcesOptions{
 		IsActive:  util.OptionalBoolTrue,
 		LoginType: SSPI,
 	}.ToConds())
 	if err != nil {
-		log.Error("Active SSPI Sources: %v", err)
+		log.Error("IsSSPIEnabled: failed to query active SSPI sources: %v", err)
 		return false
 	}
 	return exist

models/db/engine.go

@@ -27,9 +27,6 @@ var (
 	x         *xorm.Engine
 	tables    []any
 	initFuncs []func() error
-
-	// HasEngine specifies if we have a xorm.Engine
-	HasEngine bool
 )
 
 // Engine represents a xorm engine or session.

modules/setting/server.go

@@ -341,8 +341,7 @@ func loadServerFrom(rootCfg ConfigProvider) {
 		LandingPageURL = LandingPageOrganizations
 	case "login":
 		LandingPageURL = LandingPageLogin
-	case "":
-	case "home":
+	case "", "home":
 		LandingPageURL = LandingPageHome
 	default:
 		LandingPageURL = LandingPage(landingPage)

routers/common/db.go

@@ -37,7 +37,6 @@ func InitDBEngine(ctx context.Context) (err error) {
 		log.Info("Backing off for %d seconds", int64(setting.Database.DBConnectBackoff/time.Second))
 		time.Sleep(setting.Database.DBConnectBackoff)
 	}
-	db.HasEngine = true
 	config.SetDynGetter(system_model.NewDatabaseDynKeyGetter())
 	return nil
 }

routers/web/auth/auth.go

@@ -45,10 +45,6 @@ const (
 
 // autoSignIn reads cookie and try to auto-login.
 func autoSignIn(ctx *context.Context) (bool, error) {
-	if !db.HasEngine {
-		return false, nil
-	}
-
 	isSucceed := false
 	defer func() {
 		if !isSucceed {
@@ -145,7 +141,11 @@ func CheckAutoLogin(ctx *context.Context) bool {
 
 	if isSucceed {
 		middleware.DeleteRedirectToCookie(ctx.Resp)
-		ctx.RedirectToFirst(redirectTo, setting.AppSubURL+string(setting.LandingPageURL))
+		nextRedirectTo := setting.AppSubURL + string(setting.LandingPageURL)
+		if setting.LandingPageURL == setting.LandingPageLogin {
+			nextRedirectTo = setting.AppSubURL + "/" // do not cycle-redirect to the login page
+		}
+		ctx.RedirectToFirst(redirectTo, nextRedirectTo)
 		return true
 	}