fix(projects): don't allow making a project child of itself

docs/content/doc/usage/errors.md

@@ -63,6 +63,7 @@ This document describes the different errors Vikunja can return.
 | 3007      | 400 | A project with this identifier already exists.                                                                                   |
 | 3008      | 412 | The project is archived and can therefore only be accessed read only. This is also true for all tasks associated with this project. |
 | 3009      | 412 | The project cannot belong to a dynamically generated namespace like "Favorites".                                                 |
+| 3010      | 412 | This project cannot be a child of itself.|
 
 ## Task
 

pkg/models/error.go

@@ -283,8 +283,35 @@ func (err *ErrProjectCannotBelongToAPseudoParentProject) HTTPError() web.HTTPErr
 	}
 }
 
+// ErrProjectCannotBeChildOfItself represents an error where a project cannot become a child of its own
+type ErrProjectCannotBeChildOfItself struct {
+	ProjectID int64
+}
+
+// IsErrProjectCannotBeChildOfItsOwn checks if an error is a project is archived error.
+func IsErrProjectCannotBeChildOfItsOwn(err error) bool {
+	_, ok := err.(*ErrProjectCannotBeChildOfItself)
+	return ok
+}
+
+func (err *ErrProjectCannotBeChildOfItself) Error() string {
+	return fmt.Sprintf("Project cannot be made a child of itself [ProjectID: %d]", err.ProjectID)
+}
+
+// ErrCodeProjectCannotBeChildOfItself holds the unique world-error code of this error
+const ErrCodeProjectCannotBeChildOfItself = 3010
+
+// HTTPError holds the http error description
+func (err *ErrProjectCannotBeChildOfItself) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusPreconditionFailed,
+		Code:     ErrCodeProjectCannotBeChildOfItself,
+		Message:  "This project cannot be a child of itself.",
+	}
+}
+
 // ==============
-// Project errors
+// Task errors
 // ==============
 
 // ErrTaskCannotBeEmpty represents a "ErrProjectDoesNotExist" kind of error. Used if the project does not exist.

pkg/models/project.go

@@ -641,6 +641,12 @@ func checkProjectBeforeUpdateOrDelete(s *xorm.Session, project *Project) error {
 
 	// Check if the parent project exists
 	if project.ParentProjectID > 0 {
+		if project.ParentProjectID == project.ID {
+			return &ErrProjectCannotBeChildOfItself{
+				ProjectID: project.ID,
+			}
+		}
+
 		_, err := GetProjectSimpleByID(s, project.ParentProjectID)
 		if err != nil {
 			return err