From 6994de4c651274a6592905c1f5d3348f303ff0b6 Mon Sep 17 00:00:00 2001
From: Chenghao Liu <chliu@stu.pku.edu.cn>
Date: Fri, 11 Sep 2026 01:08:43 +0800
Subject: [PATCH] fix: support unhashable callable tools

Signed-off-by: Chenghao Liu <chliu@stu.pku.edu.cn>
---
 src/google/adk/tools/function_tool.py       |  8 ++++-
 src/google/adk/utils/_callable_utils.py     |  9 +++++-
 tests/unittests/tools/test_function_tool.py | 33 +++++++++++++++++++++
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/src/google/adk/tools/function_tool.py b/src/google/adk/tools/function_tool.py
index 266a97c2d62..3f8eb1530df 100644
--- a/src/google/adk/tools/function_tool.py
+++ b/src/google/adk/tools/function_tool.py
@@ -130,7 +130,13 @@ def _get_declaration(self) -> Optional[types.FunctionDeclaration]:
     # `ignore_params` drops the function context and input_stream (for streaming
     # tools), which the model doesn't understand. Return a copy: the cached
     # declaration is shared and callers (e.g. toolset prefixing) mutate it.
-    declaration = _build_declaration_cached(
+    try:
+      hash(self.func)
+    except TypeError:
+      build_declaration = _build_declaration_cached.__wrapped__
+    else:
+      build_declaration = _build_declaration_cached
+    declaration = build_declaration(
         self.func,
         tuple(self._ignore_params),
         self._api_variant,
diff --git a/src/google/adk/utils/_callable_utils.py b/src/google/adk/utils/_callable_utils.py
index 44b221d7919..5c85b50cebd 100644
--- a/src/google/adk/utils/_callable_utils.py
+++ b/src/google/adk/utils/_callable_utils.py
@@ -145,7 +145,14 @@ def __init__(self, func: Callable[..., Any] | None) -> None:
       self.doc = doc
 
       # Context parameter detection
-      self.context_param_name = context_utils.find_context_parameter(func)
+      try:
+        hash(func)
+      except TypeError:
+        # Callable instances (e.g. dataclasses) need not be hashable.
+        find_context = context_utils.find_context_parameter.__wrapped__
+      else:
+        find_context = context_utils.find_context_parameter
+      self.context_param_name = find_context(func)
 
       # Resolve signature presence at initialization
       try:
diff --git a/tests/unittests/tools/test_function_tool.py b/tests/unittests/tools/test_function_tool.py
index eaa97531cd5..e5d64314565 100644
--- a/tests/unittests/tools/test_function_tool.py
+++ b/tests/unittests/tools/test_function_tool.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import dataclasses
 import inspect
 from typing import Any
 from typing import Optional
@@ -20,6 +21,7 @@
 
 from google.adk.agents.context import Context
 from google.adk.agents.invocation_context import InvocationContext
+from google.adk.models.llm_request import LlmRequest
 from google.adk.sessions.session import Session
 from google.adk.tools.function_tool import _build_declaration_cached
 from google.adk.tools.function_tool import FunctionTool
@@ -567,6 +569,37 @@ def sample_tool(a: int, b: str) -> str:
   assert d3.name == "sample_tool"
 
 
+@pytest.mark.parametrize("bound_method", [False, True])
+async def test_unhashable_callable_can_be_declared_and_invoked(
+    bound_method, mock_tool_context
+):
+  """Dataclass tools and their bound methods remain usable in LLM requests."""
+
+  @dataclasses.dataclass
+  class Search:
+    prefix: str
+
+    def __call__(self, query: str) -> str:
+      """Search for a query."""
+      return self.prefix + query
+
+  search = Search(prefix="found: ")
+  tool = FunctionTool(search.__call__ if bound_method else search)
+  first = LlmRequest()
+  first.append_tools([tool])
+  first.config.tools[0].function_declarations[0].name = "prefixed_search"
+  second = LlmRequest()
+  second.append_tools([tool])
+  result = await tool.run_async(
+      args={"query": "hello"}, tool_context=mock_tool_context
+  )
+
+  declaration = second.config.tools[0].function_declarations[0]
+  assert declaration.name == tool.name
+  assert "query" in declaration.parameters_json_schema["properties"]
+  assert result == "found: hello"
+
+
 @pytest.mark.asyncio
 async def test_run_async_with_async_generator_streaming_tool(mock_tool_context):
   """Test that run_async returns an AsyncGenerator when wrapped function is an async generator."""