Replace -1 with GhostUserID (#27703)

models/user/user_system.go

@@ -9,12 +9,18 @@ import (
 	"code.gitea.io/gitea/modules/structs"
 )
 
+const (
+	GhostUserID        = -1
+	GhostUserName      = "Ghost"
+	GhostUserLowerName = "ghost"
+)
+
 // NewGhostUser creates and returns a fake user for someone has deleted their account.
 func NewGhostUser() *User {
 	return &User{
-		ID:        -1,
-		Name:      "Ghost",
-		LowerName: "ghost",
+		ID:        GhostUserID,
+		Name:      GhostUserName,
+		LowerName: GhostUserLowerName,
 	}
 }
 
@@ -23,13 +29,13 @@ func (u *User) IsGhost() bool {
 	if u == nil {
 		return false
 	}
-	return u.ID == -1 && u.Name == "Ghost"
+	return u.ID == GhostUserID && u.Name == GhostUserName
 }
 
 // NewReplaceUser creates and returns a fake user for external user
 func NewReplaceUser(name string) *User {
 	return &User{
-		ID:        -1,
+		ID:        0,
 		Name:      name,
 		LowerName: strings.ToLower(name),
 	}