[IMP] project: check no cyclic task dependencies

Before this commit, if we have for instance 3 tasks called A, B and C
where A depends on B and B depends on A then we have a cyclic dependency.
Another example with the same tasks, we can have a cyclic dependency if
A depends on B, B depends on C and C depends on A.

This commit checks we have no cyclic dependencies when the user adds a
dependency on a task.

task-2387984

closes #66740

addons/project/models/project.py

@@ -737,6 +737,11 @@ class Task(models.Model):
     repeat_show_week = fields.Boolean(compute='_compute_repeat_visibility')
     repeat_show_month = fields.Boolean(compute='_compute_repeat_visibility')
 
+    @api.constrains('depend_on_ids')
+    def _check_no_cyclic_dependencies(self):
+        if not self._check_m2m_recursion('depend_on_ids'):
+            raise ValidationError(_("You cannot create cyclic dependency."))
+
     @api.model
     def _get_recurrence_fields(self):
         return ['repeat_interval', 'repeat_unit', 'repeat_type', 'repeat_until', 'repeat_number',

addons/project/tests/test_task_dependencies.py

@@ -40,3 +40,48 @@ class TestTaskDependencies(TestProjectCommon):
             'depend_on_ids': [Command.link(self.task_3.id)],
         })
         self.assertEqual(len(self.task_1.depend_on_ids), 2, "The task 1 should have two dependencies.")
+
+    def test_cyclic_dependencies(self):
+        """ Test the cyclic dependencies
+
+            Test Case:
+            =========
+            1) Check initial setting on three tasks
+            2) Add task2 as dependency in task1
+            3) Add task3 as dependency in task2
+            4) Add task1 as dependency in task3 and check a validation error is raised
+            5) Add task1 as dependency in task2 and check a validation error is raised
+        """
+        # 1) Check initial setting on three tasks
+        self.assertTrue(
+            len(self.task_1.depend_on_ids) == len(self.task_2.depend_on_ids) == len(self.task_3.depend_on_ids) == 0,
+            "The three tasks should depend on no tasks.")
+        self.assertTrue(self.task_1.allow_task_dependencies, 'The task dependencies feature should be enable.')
+        self.assertTrue(self.task_2.allow_task_dependencies, 'The task dependencies feature should be enable.')
+        self.assertTrue(self.task_3.allow_task_dependencies, 'The task dependencies feature should be enable.')
+
+        # 2) Add task2 as dependency in task1
+        self.task_1.write({
+            'depend_on_ids': [Command.link(self.task_2.id)],
+        })
+        self.assertEqual(len(self.task_1.depend_on_ids), 1, 'The task 1 should have one dependency.')
+
+        # 3) Add task3 as dependency in task2
+        self.task_2.write({
+            'depend_on_ids': [Command.link(self.task_3.id)],
+        })
+        self.assertEqual(len(self.task_2.depend_on_ids), 1, "The task 2 should have one dependency.")
+
+        # 4) Add task1 as dependency in task3 and check a validation error is raised
+        with self.assertRaises(ValidationError), self.cr.savepoint():
+            self.task_3.write({
+                'depend_on_ids': [Command.link(self.task_1.id)],
+            })
+        self.assertEqual(len(self.task_3.depend_on_ids), 0, "The dependency should not be added in the task 3 because of a cyclic dependency.")
+
+        # 5) Add task1 as dependency in task2 and check a validation error is raised
+        with self.assertRaises(ValidationError), self.cr.savepoint():
+            self.task_2.write({
+                'depend_on_ids': [Command.link(self.task_1.id)],
+            })
+        self.assertEqual(len(self.task_2.depend_on_ids), 1, "The number of dependencies should no change in the task 2 because of a cyclic dependency.")