fix(google): reject ambiguous Gemini plugin names

python/semantic_kernel/connectors/ai/google/google_ai/services/utils.py

@@ -14,6 +14,7 @@
     FUNCTION_CHOICE_TYPE_TO_GOOGLE_FUNCTION_CALLING_MODE,
     GEMINI_FUNCTION_NAME_SEPARATOR,
     sanitize_schema_for_google_ai,
+    validate_gemini_plugin_name,
 )
 from semantic_kernel.contents.chat_message_content import ChatMessageContent
 from semantic_kernel.contents.function_call_content import FunctionCallContent
@@ -148,6 +149,7 @@ def format_tool_message(message: ChatMessageContent) -> list[Part]:
 
 def kernel_function_metadata_to_google_ai_function_call_format(metadata: KernelFunctionMetadata) -> dict[str, Any]:
     """Convert the kernel function metadata to function calling format."""
+    validate_gemini_plugin_name(metadata.plugin_name)
     parameters: dict[str, Any] | None = None
     if metadata.parameters:
         properties = {}

python/semantic_kernel/connectors/ai/google/shared_utils.py

@@ -41,10 +41,22 @@ def filter_system_message(chat_history: ChatHistory) -> str | None:
 # This is required since Gemini doesn't work well with "-" in the function name.
 # https://ai.google.dev/gemini-api/docs/function-calling#function_declarations
 # Using double underscore to avoid situations where the function name already contains a single underscore.
-# For example, we may incorrect split a function name with a single score when the function doesn't have a plugin name.
+# A plugin name ending in a single underscore is also unsafe because its suffix
+# overlaps the leading underscore of the separator.
 GEMINI_FUNCTION_NAME_SEPARATOR = "__"
 
 
+def validate_gemini_plugin_name(plugin_name: str | None) -> None:
+    """Reject plugin names that collide with Gemini's function-name separator."""
+    if plugin_name and (
+        GEMINI_FUNCTION_NAME_SEPARATOR in plugin_name or plugin_name.endswith("_")
+    ):
+        raise ServiceInvalidRequestError(
+            f"Gemini function names use '{GEMINI_FUNCTION_NAME_SEPARATOR}' to separate plugin and function names; "
+            f"plugin name {plugin_name!r} contains that separator and cannot be represented safely."
+        )
+
+
 def format_gemini_function_name_to_kernel_function_fully_qualified_name(gemini_function_name: str) -> str:
     """Format the Gemini function name to the kernel function fully qualified name."""
     if GEMINI_FUNCTION_NAME_SEPARATOR in gemini_function_name:

python/semantic_kernel/connectors/ai/google/vertex_ai/services/utils.py

@@ -12,6 +12,7 @@
     FUNCTION_CHOICE_TYPE_TO_GOOGLE_FUNCTION_CALLING_MODE,
     GEMINI_FUNCTION_NAME_SEPARATOR,
     sanitize_schema_for_google_ai,
+    validate_gemini_plugin_name,
 )
 from semantic_kernel.connectors.ai.google.vertex_ai.vertex_ai_prompt_execution_settings import (
     VertexAIChatPromptExecutionSettings,
@@ -138,6 +139,7 @@ def format_tool_message(message: ChatMessageContent) -> list[Part]:
 
 def kernel_function_metadata_to_vertex_ai_function_call_format(metadata: KernelFunctionMetadata) -> FunctionDeclaration:
     """Convert the kernel function metadata to function calling format."""
+    validate_gemini_plugin_name(metadata.plugin_name)
     properties: dict[str, Any] = {}
     if metadata.parameters:
         for param in metadata.parameters:

python/tests/unit/connectors/ai/google/google_ai/services/test_google_ai_utils.py

@@ -199,3 +199,27 @@ def test_google_ai_function_call_format_empty_parameters() -> None:
     )
     result = kernel_function_metadata_to_google_ai_function_call_format(metadata)
     assert result["parameters"] is None
+
+
+def test_google_ai_function_call_format_rejects_ambiguous_plugin_name() -> None:
+    metadata = KernelFunctionMetadata(
+        name="time",
+        plugin_name="utils__get",
+        description="Ambiguous plugin name",
+        is_prompt=False,
+    )
+
+    with pytest.raises(ServiceInvalidRequestError, match="cannot be represented safely"):
+        kernel_function_metadata_to_google_ai_function_call_format(metadata)
+
+
+def test_google_ai_function_call_format_rejects_plugin_name_ending_in_separator_prefix() -> None:
+    metadata = KernelFunctionMetadata(
+        name="time",
+        plugin_name="utils_",
+        description="Plugin name overlaps the separator prefix",
+        is_prompt=False,
+    )
+
+    with pytest.raises(ServiceInvalidRequestError, match="cannot be represented safely"):
+        kernel_function_metadata_to_google_ai_function_call_format(metadata)

python/tests/unit/connectors/ai/google/vertex_ai/services/test_vertex_ai_utils.py

@@ -197,3 +197,27 @@ def test_vertex_ai_function_call_format_empty_parameters() -> None:
     )
     result = kernel_function_metadata_to_vertex_ai_function_call_format(metadata)
     assert isinstance(result, FunctionDeclaration)
+
+
+def test_vertex_ai_function_call_format_rejects_ambiguous_plugin_name() -> None:
+    metadata = KernelFunctionMetadata(
+        name="time",
+        plugin_name="utils__get",
+        description="Ambiguous plugin name",
+        is_prompt=False,
+    )
+
+    with pytest.raises(ServiceInvalidRequestError, match="cannot be represented safely"):
+        kernel_function_metadata_to_vertex_ai_function_call_format(metadata)
+
+
+def test_vertex_ai_function_call_format_rejects_plugin_name_ending_in_separator_prefix() -> None:
+    metadata = KernelFunctionMetadata(
+        name="time",
+        plugin_name="utils_",
+        description="Plugin name overlaps the separator prefix",
+        is_prompt=False,
+    )
+
+    with pytest.raises(ServiceInvalidRequestError, match="cannot be represented safely"):
+        kernel_function_metadata_to_vertex_ai_function_call_format(metadata)