Update validators and tests

src/crewai/crew.py

@@ -276,15 +276,39 @@ class Crew(BaseModel):
         return self
 
     @model_validator(mode="after")
-    def validate_async_task_cannot_include_async_tasks_in_context(self):
+    def validate_async_task_cannot_include_sequential_async_tasks_in_context(self):
-        """Validates that if a task is set to be executed asynchronously, it cannot include other asynchronous tasks in its context."""
+        """
-        for task in self.tasks:
+        Validates that if a task is set to be executed asynchronously,
+        it cannot include other asynchronous tasks in its context unless
+        separated by a synchronous task.
+        """
+        for i, task in enumerate(self.tasks):
             if task.async_execution and task.context:
-                async_tasks_in_context = [t for t in task.context if t.async_execution]
+                for context_task in task.context:
-                if async_tasks_in_context:
+                    if context_task.async_execution:
-                    raise ValueError(
+                        for j in range(i - 1, -1, -1):
-                        f"Task '{task.description}' is asynchronous and cannot include other asynchronous tasks in its context."
+                            if self.tasks[j] == context_task:
-                    )
+                                raise ValueError(
+                                    f"Task '{task.description}' is asynchronous and cannot include other sequential asynchronous tasks in its context."
+                                )
+                            if not self.tasks[j].async_execution:
+                                break
+        return self
+
+    @model_validator(mode="after")
+    def validate_context_no_future_tasks(self):
+        """Validates that a task's context does not include future tasks."""
+        task_indices = {id(task): i for i, task in enumerate(self.tasks)}
+
+        for task in self.tasks:
+            if task.context:
+                for context_task in task.context:
+                    if id(context_task) not in task_indices:
+                        continue  # Skip context tasks not in the main tasks list
+                    if task_indices[id(context_task)] > task_indices[id(task)]:
+                        raise ValueError(
+                            f"Task '{task.description}' has a context dependency on a future task '{context_task.description}', which is not allowed."
+                        )
         return self
 
     def _setup_from_config(self):

tests/crew_test.py

@@ -7,6 +7,7 @@ from unittest.mock import patch
 
 import pydantic_core
 import pytest
+
 from crewai.agent import Agent
 from crewai.agents.cache import CacheHandler
 from crewai.crew import Crew
@@ -86,7 +87,7 @@ def test_crew_config_conditional_requirement():
     ]
 
 
-def test_async_task_context_validation():
+def test_async_task_cannot_include_sequential_async_tasks_in_context():
     task1 = Task(
         description="Task 1",
         async_execution=True,
@@ -102,15 +103,69 @@ def test_async_task_context_validation():
     )
     task3 = Task(
         description="Task 3",
+        async_execution=True,
+        expected_output="output",
+        agent=researcher,
+        context=[task2],
+    )
+    task4 = Task(
+        description="Task 4",
+        expected_output="output",
+        agent=writer,
+    )
+    task5 = Task(
+        description="Task 5",
+        async_execution=True,
+        expected_output="output",
+        agent=researcher,
+        context=[task4],
+    )
+
+    # This should raise an error because task2 is async and has task1 in its context without a sync task in between
+    with pytest.raises(
+        ValueError,
+        match="Task 'Task 2' is asynchronous and cannot include other sequential asynchronous tasks in its context.",
+    ):
+        Crew(tasks=[task1, task2, task3, task4, task5], agents=[researcher, writer])
+
+    # This should not raise an error because task5 has a sync task (task4) in its context
+    try:
+        Crew(tasks=[task1, task4, task5], agents=[researcher, writer])
+    except ValueError:
+        pytest.fail("Unexpected ValidationError raised")
+
+
+def test_context_no_future_tasks():
+
+    task2 = Task(
+        description="Task 2",
         expected_output="output",
         agent=researcher,
     )
+    task3 = Task(
+        description="Task 3",
+        expected_output="output",
+        agent=researcher,
+        context=[task2],
+    )
+    task4 = Task(
+        description="Task 4",
+        expected_output="output",
+        agent=researcher,
+    )
+    task1 = Task(
+        description="Task 1",
+        expected_output="output",
+        agent=researcher,
+        context=[task4],
+    )
 
+    # This should raise an error because task1 has a context dependency on a future task (task4)
     with pytest.raises(
         ValueError,
-        match="Task 'Task 2' is asynchronous and cannot include other asynchronous tasks in its context.",
+        match="Task 'Task 1' has a context dependency on a future task 'Task 4', which is not allowed.",
     ):
-        Crew(tasks=[task1, task2, task3], agents=[researcher, writer])
+        Crew(tasks=[task1, task2, task3, task4], agents=[researcher, writer])
 
 
 def test_crew_config_with_wrong_keys():