fix: handles function tool parsing corner case where type hints are stored as strings.

Previously if you add `from __future__ import annotations` in your code, the parsing code would fail because the type hints will be a string instead of the class itself (e.g. input: 'str' instead of input: str).

Also added "_" to the util file name.

PiperOrigin-RevId: 764817339

src/google/adk/tools/_automatic_function_calling_util.py

@@ -16,6 +16,7 @@ from __future__ import annotations
 
 import inspect
 from types import FunctionType
+import typing
 from typing import Any
 from typing import Callable
 from typing import Dict
@@ -29,7 +30,7 @@ from pydantic import BaseModel
 from pydantic import create_model
 from pydantic import fields as pydantic_fields
 
-from . import function_parameter_parse_util
+from . import _function_parameter_parse_util
 
 _py_type_2_schema_type = {
     'str': types.Type.STRING,
@@ -306,7 +307,11 @@ def from_function_with_options(
         inspect.Parameter.KEYWORD_ONLY,
         inspect.Parameter.POSITIONAL_ONLY,
     ):
-      schema = function_parameter_parse_util._parse_schema_from_parameter(
+      # This snippet catches the case when type hints are stored as strings
+      if isinstance(param.annotation, str):
+        param = param.replace(annotation=typing.get_type_hints(func)[name])
+
+      schema = _function_parameter_parse_util._parse_schema_from_parameter(
           variant, param, func.__name__
       )
       parameters_properties[name] = schema
@@ -320,7 +325,7 @@ def from_function_with_options(
         properties=parameters_properties,
     )
     declaration.parameters.required = (
-        function_parameter_parse_util._get_required_fields(
+        _function_parameter_parse_util._get_required_fields(
             declaration.parameters
         )
     )
@@ -331,14 +336,19 @@ def from_function_with_options(
   if return_annotation is inspect._empty:
     return declaration
 
+  return_value = inspect.Parameter(
+      'return_value',
+      inspect.Parameter.POSITIONAL_OR_KEYWORD,
+      annotation=return_annotation,
+  )
+  # This snippet catches the case when type hints are stored as strings
+  if isinstance(return_value.annotation, str):
+    return_value = return_value.replace(annotation=typing.get_type_hints(func)["return"])
+
   declaration.response = (
-      function_parameter_parse_util._parse_schema_from_parameter(
+      _function_parameter_parse_util._parse_schema_from_parameter(
           variant,
-          inspect.Parameter(
-              'return_value',
-              inspect.Parameter.POSITIONAL_OR_KEYWORD,
-              annotation=return_annotation,
-          ),
+          return_value,
           func.__name__,
       )
   )

src/google/adk/tools/_function_parameter_parse_util.py

@@ -13,6 +13,8 @@
 # limitations under the License.
 #
 
+from __future__ import annotations
+
 import inspect
 import logging
 import types as typing_types