Gemini function calling mode exp (#2795)

* Gemini function calling mode exp

* add config to package.json

* Make setting internal only

* add setting that was removed accidentally

---------

Co-authored-by: vijay upadya <vj@example.com>

Author: vijayupadya

src/platform/configuration/common/configurationService.ts

@@ -734,9 +734,9 @@ export namespace ConfigKey {
 		export const InternalWelcomeHintEnabled = defineTeamInternalSetting<boolean>('chat.advanced.welcomePageHint.enabled', ConfigType.Simple, { defaultValue: false, internalDefaultValue: true, teamDefaultValue: true, owner: 'lramos15', expirationDate: '2025-01-01' /* exempted */ });
 		export const InlineChatUseCodeMapper = defineTeamInternalSetting<boolean>('chat.advanced.inlineChat.useCodeMapper', ConfigType.Simple, false);
 		export const EnablePromptRendererTracing = defineTeamInternalSetting<boolean>('chat.advanced.promptRenderer.trace', ConfigType.Simple, false);
-
 		// Backed by Experiments
 		export const DebugCollectFetcherTelemetry = defineTeamInternalSetting<boolean>('chat.advanced.debug.collectFetcherTelemetry', ConfigType.ExperimentBased, true);
+		export const GeminiFunctionCallingMode = defineTeamInternalSetting<'auto' | 'none' | 'required' | 'validated' | undefined>('chat.advanced.gemini.functionCallingMode', ConfigType.ExperimentBased, undefined);
 		export const DebugExpUseNodeFetchFetcher = defineTeamInternalSetting<boolean | undefined>('chat.advanced.debug.useNodeFetchFetcher', ConfigType.ExperimentBased, undefined);
 		export const DebugExpUseNodeFetcher = defineTeamInternalSetting<boolean | undefined>('chat.advanced.debug.useNodeFetcher', ConfigType.ExperimentBased, undefined);
 		export const DebugExpUseElectronFetcher = defineTeamInternalSetting<boolean | undefined>('chat.advanced.debug.useElectronFetcher', ConfigType.ExperimentBased, undefined);

src/platform/endpoint/node/responsesApi.ts

@@ -31,6 +31,12 @@ export function createResponsesRequestBody(accessor: ServicesAccessor, options:
 	const configService = accessor.get(IConfigurationService);
 	const expService = accessor.get(IExperimentationService);
 	const verbosity = getVerbosityForModelSync(endpoint);
+
+	const hasTools = !!options.requestOptions?.tools?.length;
+	const geminiFunctionCallingMode = hasTools && endpoint.family.toLowerCase().includes('gemini-3')
+		? configService.getExperimentBasedConfig(ConfigKey.TeamInternal.GeminiFunctionCallingMode, expService)
+		: undefined;
+
 	const body: IEndpointBody = {
 		model,
 		...rawMessagesToResponseAPI(model, options.messages, !!options.ignoreStatefulMarker),
@@ -44,9 +50,11 @@ export function createResponsesRequestBody(accessor: ServicesAccessor, options:
 		// Only a subset of completion post options are supported, and some
 		// are renamed. Handle them manually:
 		max_output_tokens: options.postOptions.max_tokens,
-		tool_choice: typeof options.postOptions.tool_choice === 'object'
-			? { type: 'function', name: options.postOptions.tool_choice.function.name }
-			: options.postOptions.tool_choice,
+		tool_choice: geminiFunctionCallingMode && typeof options.postOptions.tool_choice !== 'object'
+			? geminiFunctionCallingMode
+			: (typeof options.postOptions.tool_choice === 'object'
+				? { type: 'function', name: options.postOptions.tool_choice.function.name }
+				: options.postOptions.tool_choice),
 		top_logprobs: options.postOptions.logprobs ? 3 : undefined,
 		store: false,
 		text: verbosity ? { verbosity } : undefined,

src/platform/networking/common/networking.ts

@@ -17,8 +17,8 @@ import { CustomModel, EndpointEditToolName } from '../../endpoint/common/endpoin
 import { ILogService } from '../../log/common/logService';
 import { ITelemetryService, TelemetryProperties } from '../../telemetry/common/telemetry';
 import { TelemetryData } from '../../telemetry/common/telemetryData';
-import { FinishedCallback, OpenAiFunctionTool, OpenAiResponsesFunctionTool, OptionalChatRequestParams, Prediction } from './fetch';
 import { AnthropicMessagesTool, ContextManagement } from './anthropic';
+import { FinishedCallback, OpenAiFunctionTool, OpenAiResponsesFunctionTool, OptionalChatRequestParams, Prediction } from './fetch';
 import { FetcherId, FetchOptions, IAbortController, IFetcherService, PaginationOptions, Response } from './fetcherService';
 import { ChatCompletion, RawMessageConversionCallback, rawMessageToCAPI } from './openai';
 
@@ -73,7 +73,7 @@ export interface IEndpointBody {
 	messages?: any[];
 	n?: number;
 	reasoning?: { effort?: string; summary?: string };
-	tool_choice?: OptionalChatRequestParams['tool_choice'] | { type: 'function'; name: string };
+	tool_choice?: OptionalChatRequestParams['tool_choice'] | { type: 'function'; name: string } | string;
 	top_logprobs?: number;
 	intent?: boolean;
 	intent_threshold?: number;