[FEATURE] Improve agent/task templating with Jinja2

Fixes #2650

- Add support for container types (List, Dict, Set)
- Add support for standard objects (datetime)
- Add support for custom objects
- Add support for conditional and loop statements
- Add support for filtering options
- Maintain backward compatibility with existing templates
- Add comprehensive tests
- Add documentation with examples

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/utilities/test_jinja_templating.py

@@ -0,0 +1,81 @@
+import pytest
+import datetime
+from pydantic import BaseModel
+from typing import List, Dict, Any
+from crewai.utilities.jinja_templating import to_jinja_template, render_template
+
+class Person(BaseModel):
+    name: str
+    age: int
+    
+    def __str__(self):
+        return f"{self.name} ({self.age})"
+
+class TestJinjaTemplating:
+    def test_to_jinja_template(self):
+        assert to_jinja_template("Hello {name}!") == "Hello {{name}}!"
+        
+        assert to_jinja_template("Hello {{name}}!") == "Hello {{name}}!"
+        
+        assert to_jinja_template("Hello {name} and {{title}}!") == "Hello {{name}} and {{title}}!"
+        
+        assert to_jinja_template("") == ""
+        
+        assert to_jinja_template("Hello world!") == "Hello world!"
+    
+    def test_render_template_simple_types(self):
+        inputs = {"name": "John", "age": 30, "active": True, "height": 1.85}
+        
+        assert render_template("Hello {name}!", inputs) == "Hello John!"
+        assert render_template("Age: {age}", inputs) == "Age: 30"
+        assert render_template("Active: {active}", inputs) == "Active: True"
+        assert render_template("Height: {height}", inputs) == "Height: 1.85"
+        
+        assert render_template("{name} is {age} years old", inputs) == "John is 30 years old"
+    
+    def test_render_template_container_types(self):
+        inputs = {
+            "items": ["apple", "banana", "orange"],
+            "person": {"name": "John", "age": 30}
+        }
+        
+        assert render_template("First item: {{items[0]}}", inputs) == "First item: apple"
+        
+        assert render_template("Person name: {{person.name}}", inputs) == "Person name: John"
+        
+        assert render_template(
+            "Items: {% for item in items %}{{item}}{% if not loop.last %}, {% endif %}{% endfor %}",
+            inputs
+        ) == "Items: apple, banana, orange"
+        
+        assert render_template(
+            "{% if items|length > 2 %}Many items{% else %}Few items{% endif %}",
+            inputs
+        ) == "Many items"
+    
+    def test_render_template_datetime(self):
+        today = datetime.datetime.now()
+        inputs = {"today": today}
+        
+        assert render_template("Today: {{today|date}}", inputs) == f"Today: {today.strftime('%Y-%m-%d')}"
+        
+        assert render_template("Today: {{today|date('%d/%m/%Y')}}", inputs) == f"Today: {today.strftime('%d/%m/%Y')}"
+    
+    def test_render_template_custom_objects(self):
+        person = Person(name="John", age=30)
+        inputs = {"person": person}
+        
+        assert render_template("Person: {person}", inputs) == "Person: John (30)"
+        
+        assert render_template("Person name: {{person.name}}", inputs) == "Person name: John"
+    
+    def test_render_template_error_handling(self):
+        inputs = {"name": "John"}
+        
+        with pytest.raises(KeyError) as excinfo:
+            render_template("Hello {age}!", inputs)
+        assert "Template variable 'age' not found" in str(excinfo.value)
+        
+        with pytest.raises(ValueError) as excinfo:
+            render_template("Hello {name}!", {})
+        assert "Inputs dictionary cannot be empty" in str(excinfo.value)

tests/utilities/test_string_utils.py

@@ -1,6 +1,7 @@
 from typing import Any, Dict, List, Union
-
+import datetime
 import pytest
+from pydantic import BaseModel
 
 from crewai.utilities.string_utils import interpolate_only
 
@@ -185,3 +186,96 @@ class TestInterpolateOnly:
             interpolate_only(template, inputs)
 
         assert "inputs dictionary cannot be empty" in str(excinfo.value).lower()
+        
+    
+    def test_container_types_list_access(self):
+        """Test accessing list items with Jinja2 syntax."""
+        template = "First item: {{items[0]}}, Second item: {{items[1]}}"
+        inputs = {
+            "items": ["apple", "banana", "orange"]
+        }
+        
+        result = interpolate_only(template, inputs)
+        assert result == "First item: apple, Second item: banana"
+    
+    def test_container_types_dict_access(self):
+        """Test accessing dictionary items with Jinja2 syntax."""
+        template = "Name: {{person.name}}, Age: {{person.age}}"
+        inputs = {
+            "person": {"name": "John", "age": 30}
+        }
+        
+        result = interpolate_only(template, inputs)
+        assert result == "Name: John, Age: 30"
+    
+    def test_conditional_statements(self):
+        """Test conditional statements with Jinja2 syntax."""
+        template = "{% if priority == 'high' %}URGENT: {% endif %}Task: {task}"
+        
+        inputs_high = {
+            "task": "Fix bug",
+            "priority": "high"
+        }
+        result_high = interpolate_only(template, inputs_high)
+        assert result_high == "URGENT: Task: Fix bug"
+        
+        inputs_low = {
+            "task": "Fix bug",
+            "priority": "low"
+        }
+        result_low = interpolate_only(template, inputs_low)
+        assert result_low == "Task: Fix bug"
+    
+    def test_loop_statements(self):
+        """Test loop statements with Jinja2 syntax."""
+        template = "Items: {% for item in items %}{{item}}{% if not loop.last %}, {% endif %}{% endfor %}"
+        inputs = {
+            "items": ["apple", "banana", "orange"]
+        }
+        
+        result = interpolate_only(template, inputs)
+        assert result == "Items: apple, banana, orange"
+    
+    def test_datetime_formatting(self):
+        """Test datetime formatting with Jinja2 filters."""
+        today = datetime.datetime(2024, 4, 20)
+        inputs = {"today": today}
+        
+        template = "Date: {{today|date}}"
+        result = interpolate_only(template, inputs)
+        assert result == "Date: 2024-04-20"
+        
+        template = "Date: {{today|date('%d/%m/%Y')}}"
+        result = interpolate_only(template, inputs)
+        assert result == "Date: 20/04/2024"
+    
+    def test_custom_objects(self):
+        """Test custom objects with Jinja2 syntax."""
+        class Person(BaseModel):
+            name: str
+            age: int
+            
+            def __str__(self):
+                return f"{self.name} ({self.age})"
+        
+        person = Person(name="John", age=30)
+        inputs = {"person": person}
+        
+        template = "Person: {person}"
+        result = interpolate_only(template, inputs)
+        assert result == "Person: John (30)"
+        
+        template = "Name: {{person.name}}, Age: {{person.age}}"
+        result = interpolate_only(template, inputs)
+        assert result == "Name: John, Age: 30"
+    
+    def test_mixed_syntax(self):
+        """Test mixed CrewAI and Jinja2 syntax."""
+        template = "Hello {name}! Items: {% for item in items %}{{item}}{% if not loop.last %}, {% endif %}{% endfor %}"
+        inputs = {
+            "name": "John",
+            "items": ["apple", "banana", "orange"]
+        }
+        
+        result = interpolate_only(template, inputs)
+        assert result == "Hello John! Items: apple, banana, orange"