fix: populate required fields in FunctionDeclaration json_schema fallback

Merge #5000

Fixes #4798 — `required` fields lost in `FunctionDeclaration` when the `parameters_json_schema` fallback path is used.

Co-authored-by: Xuan Yang <xygoogle@google.com>
COPYBARA_INTEGRATE_REVIEW=#5000 from giulio-leone:fix/required-fields-json-schema-fallback e9783d7
PiperOrigin-RevId: 899243799

Author: 2 people

src/google/adk/tools/_automatic_function_calling_util.py

@@ -368,6 +368,11 @@ def from_function_with_options(
           parameters_json_schema[name] = types.Schema.model_validate(
               json_schema_dict
           )
+          if param.default is not inspect.Parameter.empty:
+            if param.default is not None:
+              parameters_json_schema[name].default = param.default
+            else:
+              parameters_json_schema[name].nullable = True
         except Exception as e:
           _function_parameter_parse_util._raise_for_unsupported_param(
               param, func.__name__, e
@@ -392,6 +397,11 @@ def from_function_with_options(
         type='OBJECT',
         properties=parameters_json_schema,
     )
+    declaration.parameters.required = (
+        _function_parameter_parse_util._get_required_fields(
+            declaration.parameters
+        )
+    )
 
   if variant == GoogleLLMVariant.GEMINI_API:
     return declaration

tests/unittests/tools/test_from_function_with_options.py

@@ -319,3 +319,45 @@ async def test_function(param: str) -> AsyncGenerator[Dict[str, str], None]:
   # VERTEX_AI should extract yield type (Dict[str, str]) from AsyncGenerator
   assert declaration.response is not None
   assert declaration.response.type == types.Type.OBJECT
+
+
+def test_required_fields_set_in_json_schema_fallback():
+  """Test that required fields are populated when the json_schema fallback path is used.
+
+  When a parameter has a complex union type (e.g. list[str] | None) that
+  _parse_schema_from_parameter can't handle, from_function_with_options falls
+  back to the parameters_json_schema branch. This test verifies that the
+  required fields are correctly populated in that fallback branch.
+  """
+
+  def complex_tool(
+      query: str,
+      mode: str = 'default',
+      tags: list[str] | None = None,
+  ) -> str:
+    """A tool where one param has a complex union type."""
+    return query
+
+  declaration = _automatic_function_calling_util.from_function_with_options(
+      complex_tool, GoogleLLMVariant.GEMINI_API
+  )
+
+  assert declaration.name == 'complex_tool'
+  assert declaration.parameters == types.Schema(
+      type=types.Type.OBJECT,
+      required=['query'],
+      properties={
+          'query': types.Schema(type=types.Type.STRING),
+          'mode': types.Schema(type=types.Type.STRING, default='default'),
+          'tags': types.Schema(
+              any_of=[
+                  types.Schema(
+                      items=types.Schema(type=types.Type.STRING),
+                      type=types.Type.ARRAY,
+                  ),
+                  types.Schema(type=types.Type.NULL),
+              ],
+              nullable=True,
+          ),
+      },
+  )