fix: warn when function calling mode is ANY with automatic function calling enabled

google/genai/_extra_utils.py

@@ -472,10 +472,13 @@ def should_disable_afc(
       not config_model.automatic_function_calling
       or config_model.automatic_function_calling.disable is None
   ):
-    return False
+    afc_disabled = False
+  else:
+    afc_disabled = bool(config_model.automatic_function_calling.disable)
 
   if (
-      config_model.automatic_function_calling.disable
+      afc_disabled
+      and config_model.automatic_function_calling
       and config_model.automatic_function_calling.maximum_remote_calls
       is not None
       # exclude the case where max_remote_calls is set to 10 by default.
@@ -496,7 +499,23 @@ def should_disable_afc(
         ' `automatic_function_calling.maximum_remote_calls` unset.'
     )
 
-  return config_model.automatic_function_calling.disable
+  if (
+      not afc_disabled
+      and config_model.tool_config
+      and config_model.tool_config.function_calling_config
+      and config_model.tool_config.function_calling_config.mode
+      in (types.FunctionCallingConfigMode.ANY, 'ANY', 'any')
+  ):
+    logger.warning(
+        '`tool_config.function_calling_config.mode` is set to `ANY` with'
+        ' automatic function calling enabled. The model is forced to call a'
+        ' function on every turn and cannot return a text response, which will'
+        ' exhaust `maximum_remote_calls` and return empty text. If you want the'
+        ' model to answer with text, use mode=`AUTO`, or disable automatic'
+        ' function calling to manually orchestrate tool calls.'
+    )
+
+  return afc_disabled
 
 
 def get_max_remote_calls_afc(

google/genai/tests/afc/test_should_disable_afc.py

@@ -16,6 +16,7 @@
 
 """Tests for should_disable_afc."""
 
+import logging
 import pytest
 from .. import pytest_helper
 from ... import types
@@ -213,3 +214,57 @@ def test_afc_enable_true_max_1():
       )
       is False
   )
+
+
+def test_afc_mode_any_warns(caplog):
+  with caplog.at_level(logging.WARNING, logger='google_genai.models'):
+    config = types.GenerateContentConfig(
+        tool_config=types.ToolConfig(
+            function_calling_config=types.FunctionCallingConfig(mode='ANY')
+        )
+    )
+    result = should_disable_afc(config)
+  assert result is False
+  assert len(caplog.records) == 1
+  assert '`tool_config.function_calling_config.mode` is set to `ANY`' in caplog.records[0].message
+
+
+def test_afc_mode_any_dict_warns(caplog):
+  with caplog.at_level(logging.WARNING, logger='google_genai.models'):
+    config = {
+        'tool_config': {
+            'function_calling_config': {'mode': 'ANY'}
+        }
+    }
+    result = should_disable_afc(config)
+  assert result is False
+  assert len(caplog.records) == 1
+  assert '`tool_config.function_calling_config.mode` is set to `ANY`' in caplog.records[0].message
+
+
+def test_afc_mode_any_disabled_no_warn(caplog):
+  with caplog.at_level(logging.WARNING, logger='google_genai.models'):
+    config = types.GenerateContentConfig(
+        tool_config=types.ToolConfig(
+            function_calling_config=types.FunctionCallingConfig(mode='ANY')
+        ),
+        automatic_function_calling=types.AutomaticFunctionCallingConfig(
+            disable=True
+        ),
+    )
+    result = should_disable_afc(config)
+  assert result is True
+  assert len(caplog.records) == 0
+
+
+def test_afc_mode_auto_no_warn(caplog):
+  with caplog.at_level(logging.WARNING, logger='google_genai.models'):
+    config = types.GenerateContentConfig(
+        tool_config=types.ToolConfig(
+            function_calling_config=types.FunctionCallingConfig(mode='AUTO')
+        )
+    )
+    result = should_disable_afc(config)
+  assert result is False
+  assert len(caplog.records) == 0
+