From 6bbbf979e7a234893b2497c6bc5786b8bbaabb69 Mon Sep 17 00:00:00 2001
From: Gautier Masse <gautieresam@gmail.com>
Date: Tue, 21 Apr 2026 10:00:41 +0200
Subject: [PATCH] fix(tools): handle tuple schemas in function parsing fallback

---
 .../tools/_function_parameter_parse_util.py   | 40 +++++++++++++++++++
 .../tools/test_from_function_with_options.py  | 38 ++++++++++++++++++
 2 files changed, 78 insertions(+)

diff --git a/src/google/adk/tools/_function_parameter_parse_util.py b/src/google/adk/tools/_function_parameter_parse_util.py
index a8e98980d5..ca2308f65f 100644
--- a/src/google/adk/tools/_function_parameter_parse_util.py
+++ b/src/google/adk/tools/_function_parameter_parse_util.py
@@ -93,6 +93,45 @@ def _add_unevaluated_items_to_fixed_len_tuple_schema(
   return json_schema
 
 
+def _normalize_tuple_schema_for_genai_schema(
+    json_schema: Any,
+) -> Any:
+  """Normalizes tuple schema keywords unsupported by `types.Schema`.
+
+  Pydantic emits `prefixItems` for fixed-length tuples. `types.Schema` does not
+  support `prefixItems`, so we convert tuple item definitions into
+  `items.anyOf`. We also drop `unevaluatedItems`, which is unsupported by
+  `types.Schema`.
+  """
+  if isinstance(json_schema, list):
+    return [
+        _normalize_tuple_schema_for_genai_schema(item)
+        for item in json_schema
+    ]
+  if not isinstance(json_schema, dict):
+    return json_schema
+
+  normalized_schema = {
+      key: _normalize_tuple_schema_for_genai_schema(value)
+      for key, value in json_schema.items()
+      if key != 'unevaluatedItems'
+  }
+
+  prefix_items = normalized_schema.pop('prefixItems', None)
+  if isinstance(prefix_items, list):
+    if len(prefix_items) == 1:
+      normalized_schema['items'] = prefix_items[0]
+    elif prefix_items:
+      normalized_schema['items'] = {'anyOf': prefix_items}
+
+  # Pydantic can emit `items: false` for tuple schemas, which is unsupported by
+  # `types.Schema`.
+  if normalized_schema.get('items') is False:
+    normalized_schema.pop('items')
+
+  return normalized_schema
+
+
 def _raise_for_unsupported_param(
     param: inspect.Parameter,
     func_name: str,
@@ -131,6 +170,7 @@ def _generate_json_schema_for_parameter(
   json_schema_dict = _add_unevaluated_items_to_fixed_len_tuple_schema(
       json_schema_dict
   )
+  json_schema_dict = _normalize_tuple_schema_for_genai_schema(json_schema_dict)
   return json_schema_dict
 
 
diff --git a/tests/unittests/tools/test_from_function_with_options.py b/tests/unittests/tools/test_from_function_with_options.py
index 537094da39..6665d0a8ca 100644
--- a/tests/unittests/tools/test_from_function_with_options.py
+++ b/tests/unittests/tools/test_from_function_with_options.py
@@ -361,3 +361,41 @@ def complex_tool(
           ),
       },
   )
+
+
+def test_tuple_types_work_in_json_schema_fallback():
+  """Test that tuple schemas work in json schema fallback."""
+
+  def generate_image(
+      prompt: str,
+      input_bytes: list[tuple[bytes, str]] | None = None,
+  ) -> dict[str, str]:
+    """Generate an image from a prompt."""
+    del input_bytes
+    return {'status': prompt}
+
+  declaration = _automatic_function_calling_util.from_function_with_options(
+      generate_image, GoogleLLMVariant.GEMINI_API
+  )
+
+  assert declaration.parameters is not None
+  assert declaration.parameters.required == ['prompt']
+  input_bytes_schema = declaration.parameters.properties['input_bytes']
+  assert input_bytes_schema.nullable is True
+  assert input_bytes_schema.any_of is not None
+
+  array_schema = next(
+      schema
+      for schema in input_bytes_schema.any_of
+      if schema.type == types.Type.ARRAY
+  )
+  assert array_schema.items is not None
+  assert array_schema.items.type == types.Type.ARRAY
+  assert array_schema.items.max_items == 2
+  assert array_schema.items.min_items == 2
+  assert array_schema.items.items is not None
+  assert array_schema.items.items.any_of is not None
+  assert len(array_schema.items.items.any_of) == 2
+  assert array_schema.items.items.any_of[0].type == types.Type.STRING
+  assert array_schema.items.items.any_of[0].format == 'binary'
+  assert array_schema.items.items.any_of[1].type == types.Type.STRING