fix: Support resolving string annotations for find_context_parameter

Co-authored-by: Xuan Yang <xygoogle@google.com>
PiperOrigin-RevId: 884686010

Author: xuanyang15

src/google/adk/utils/context_utils.py

@@ -22,6 +22,7 @@
 
 from contextlib import aclosing
 import inspect
+import typing
 from typing import Any
 from typing import Callable
 from typing import get_args
@@ -80,7 +81,17 @@ def find_context_parameter(func: Callable[..., Any]) -> str | None:
     signature = inspect.signature(func)
   except (ValueError, TypeError):
     return None
+  # Resolve string annotations (e.g., 'Context')
+  try:
+    type_hints = typing.get_type_hints(func)
+  except Exception:
+    # get_type_hints can fail for various reasons (e.g., unresolvable forward
+    # references). In such cases, we fall back to inspecting the parameter
+    # annotations directly.
+    type_hints = {}
+
   for name, param in signature.parameters.items():
-    if _is_context_type(param.annotation):
+    annotation = type_hints.get(name, param.annotation)
+    if _is_context_type(annotation):
       return name
   return None

tests/unittests/utils/test_context_utils.py

@@ -33,6 +33,30 @@ def my_tool(query: str, ctx: Context) -> str:
 
     assert find_context_parameter(my_tool) == 'ctx'
 
+  def test_find_context_parameter_with_string_annotation(self):
+    """Test detection of string annotation 'Context'."""
+
+    def my_tool(query: str, ctx: 'Context') -> str:
+      return query
+
+    assert find_context_parameter(my_tool) == 'ctx'
+
+  def test_find_context_parameter_with_string_tool_context(self):
+    """Test detection of string annotation 'ToolContext'."""
+
+    def my_tool(query: str, ctx: 'ToolContext') -> str:
+      return query
+
+    assert find_context_parameter(my_tool) == 'ctx'
+
+  def test_find_context_parameter_with_string_optional_context(self):
+    """Test detection of string annotation 'Optional[Context]'."""
+
+    def my_tool(query: str, ctx: 'Optional[Context]' = None) -> str:
+      return query
+
+    assert find_context_parameter(my_tool) == 'ctx'
+
   def test_find_context_parameter_with_tool_context_type(self):
     """Test detection of ToolContext type annotation."""