feat: Make gemini accept the openai parameter parallel_tool_calls (#11125)

* feat: Make gemini accept the openai parameter parallel_tool_calls

When mapping, allow the parameter: True because that is the
intrinsic behavior of Gemini. Allow False, but reject if there
are multiple tools because there's no actual equivalent in Gemini.

fixes #9686

ref: issues/9686

* chore: cleanup and move test_vertex.py down to tests/litellm

as suggested in https://github.com/BerriAI/litellm/pull/11125#discussion_r2105905871

litellm/llms/gemini/chat/transformation.py

@@ -83,6 +83,7 @@ class GoogleAIStudioGeminiConfig(VertexGeminiConfig):
             "logprobs",
             "frequency_penalty",
             "modalities",
+            "parallel_tool_calls",
         ]
         if supports_reasoning(model):
             supported_params.append("reasoning_effort")

litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py

@@ -219,6 +219,7 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
             "logprobs",
             "top_logprobs",
             "modalities",
+            "parallel_tool_calls",
         ]
         if supports_reasoning(model):
             supported_params.append("reasoning_effort")
@@ -463,6 +464,19 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
                 )
                 if _tool_choice_value is not None:
                     optional_params["tool_choice"] = _tool_choice_value
+            elif param == "parallel_tool_calls":
+                if value is False:
+                    tools = non_default_params.get("tools", non_default_params.get("functions"))
+                    num_function_declarations = len(tools) if isinstance(tools, list) else 0
+                    if num_function_declarations > 1:
+                        raise litellm.utils.UnsupportedParamsError(
+                            message=(
+                                "`parallel_tool_calls=False` is not supported when multiple tools are "
+                                "provided for Gemini. Specify a single tool, or set "
+                                "`parallel_tool_calls=True`."
+                            ),
+                            status_code=400,
+                        )
             elif param == "seed":
                 optional_params["seed"] = value
             elif param == "reasoning_effort" and isinstance(value, str):

tests/litellm/llms/vertex_ai/test_vertex.py

@@ -12,8 +12,7 @@ import litellm.litellm_core_utils.prompt_templates
 import litellm.litellm_core_utils.prompt_templates.factory
 
 load_dotenv()
-import io
-from unittest.mock import AsyncMock, MagicMock, patch
+from unittest.mock import MagicMock
 
 sys.path.insert(
     0, os.path.abspath("../..")
@@ -21,10 +20,8 @@ sys.path.insert(
 import pytest
 import litellm
 from litellm import get_optional_params
-from litellm.llms.custom_httpx.http_handler import HTTPHandler
 from litellm.llms.vertex_ai.gemini.transformation import _process_gemini_image
-from litellm.types.llms.vertex_ai import PartType, BlobType
-import httpx
+from litellm.types.llms.vertex_ai import BlobType
 
 
 def encode_image_to_base64(image_path):
@@ -1146,7 +1143,7 @@ def test_process_gemini_image():
     from litellm.llms.vertex_ai.gemini.transformation import (
         _process_gemini_image,
     )
-    from litellm.types.llms.vertex_ai import PartType, FileDataType, BlobType
+    from litellm.types.llms.vertex_ai import FileDataType
 
     # Test GCS URI
     gcs_result = _process_gemini_image("gs://bucket/image.png")
@@ -1271,10 +1268,6 @@ def test_vertex_embedding_url(model, expected_url):
 
 import pytest
 from unittest.mock import Mock, patch
-from typing import Dict, Any
-
-# Import your actual module here
-# from your_module import _process_gemini_image, PartType, FileDataType, BlobType
 
 
 # Add these fixtures below existing fixtures
@@ -1409,3 +1402,64 @@ def test_aaavertex_embeddings_distances(
         text_embedding = text_response.data[0].embedding
 
 
+def test_vertex_parallel_tool_calls_true():
+    """
+    Test that parallel_tool_calls = True sets the correct tool_config.
+    """
+    tools = [
+        {"type": "function", "function": {"name": "get_weather"}},
+        {"type": "function", "function": {"name": "get_time"}},
+    ]
+    optional_params = get_optional_params(
+        model="gemini-1.5-pro",
+        custom_llm_provider="vertex_ai",
+        tools=tools,
+        parallel_tool_calls=True,
+    )
+    assert "tools" in optional_params
+
+
+def test_vertex_parallel_tool_calls_false_multiple_tools_error():
+    """
+    Test that parallel_tool_calls = False with multiple tools raises UnsupportedParamsError
+    when drop_params is False.
+    """
+    tools = [
+        {"type": "function", "function": {"name": "get_weather"}},
+        {"type": "function", "function": {"name": "get_time"}},
+    ]
+    with pytest.raises(litellm.utils.UnsupportedParamsError) as excinfo:
+        get_optional_params(
+            model="gemini-1.5-pro",
+            custom_llm_provider="vertex_ai",
+            tools=tools,
+            parallel_tool_calls=False,
+        )
+    assert "`parallel_tool_calls=False` is not supported when multiple tools are provided" in str(excinfo.value)
+
+    # works when specified as "functions"
+    with pytest.raises(litellm.utils.UnsupportedParamsError) as excinfo:
+        get_optional_params(
+            model="gemini-1.5-pro",
+            custom_llm_provider="vertex_ai",
+            functions=tools,
+            parallel_tool_calls=False,
+        )
+    assert "`parallel_tool_calls=False` is not supported when multiple tools are provided" in str(excinfo.value)
+
+
+def test_vertex_parallel_tool_calls_false_single_tool():
+    """
+    Test that parallel_tool_calls = False with a single tool does not raise an error
+    and does not add 'tool_config' if not otherwise specified.
+    """
+    tools = [
+        {"type": "function", "function": {"name": "get_weather"}},
+    ]
+    optional_params = get_optional_params(
+        model="gemini-1.5-pro",
+        custom_llm_provider="vertex_ai",
+        tools=tools,
+        parallel_tool_calls=False,
+    )
+    assert "tools" in optional_params