Call Gemini function even when text part is returned

* add tests

Closes gh-2499

Signed-off-by: Vlad Stoian <[email protected]>

Author: vlad-stoian

models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatModel.java

@@ -20,6 +20,7 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
@@ -587,35 +588,27 @@ protected List<Generation> responseCandidateToGeneration(Candidate candidate) {
 			.finishReason(candidateFinishReason.name())
 			.build();
 
-		boolean isFunctionCall = candidate.getContent().getPartsList().stream().allMatch(Part::hasFunctionCall);
-
-		if (isFunctionCall) {
-			List<AssistantMessage.ToolCall> assistantToolCalls = candidate.getContent()
-				.getPartsList()
-				.stream()
-				.filter(part -> part.hasFunctionCall())
-				.map(part -> {
-					FunctionCall functionCall = part.getFunctionCall();
-					var functionName = functionCall.getName();
-					String functionArguments = structToJson(functionCall.getArgs());
-					return new AssistantMessage.ToolCall("", "function", functionName, functionArguments);
-				})
-				.toList();
+		var assistantToolCalls = candidate.getContent()
+			.getPartsList()
+			.stream()
+			.filter(Part::hasFunctionCall)
+			.map(part -> {
+				FunctionCall functionCall = part.getFunctionCall();
+				var functionName = functionCall.getName();
+				String functionArguments = structToJson(functionCall.getArgs());
+				return new AssistantMessage.ToolCall("", "function", functionName, functionArguments);
+			})
+			.toList();
 
-			AssistantMessage assistantMessage = new AssistantMessage("", messageMetadata, assistantToolCalls);
+		var text = candidate.getContent()
+			.getPartsList()
+			.stream()
+			.filter(Part::hasText)
+			.map(Part::getText)
+			.collect(Collectors.joining(System.lineSeparator()));
 
-			return List.of(new Generation(assistantMessage, chatGenerationMetadata));
-		}
-		else {
-			List<Generation> generations = candidate.getContent()
-				.getPartsList()
-				.stream()
-				.map(part -> new AssistantMessage(part.getText(), messageMetadata))
-				.map(assistantMessage -> new Generation(assistantMessage, chatGenerationMetadata))
-				.toList();
-
-			return generations;
-		}
+		return List.of(new Generation(new AssistantMessage(text, messageMetadata, assistantToolCalls),
+				chatGenerationMetadata));
 	}
 
 	private ChatResponseMetadata toChatResponseMetadata(Usage usage) {

models/spring-ai-vertex-ai-gemini/src/test/java/org/springframework/ai/vertexai/gemini/tool/VertexAiGeminiChatModelToolCallingIT.java

@@ -96,6 +96,30 @@ public void functionCallExplicitOpenApiSchema() {
 		assertThat(response.getResult().getOutput().getText()).contains("30", "10", "15");
 	}
 
+	@Test
+	public void functionCallModelReturnsMixedTextAndFunctionCallParts() {
+		UserMessage userMessage = new UserMessage(
+				"What can you tell me about the temperature in San Francisco, Paris and in Tokyo? Return the temperature in Celsius. Expose your thinking process.");
+
+		List<Message> messages = new ArrayList<>(List.of(userMessage));
+
+		var promptOptions = VertexAiGeminiChatOptions.builder()
+			.model(VertexAiGeminiChatModel.ChatModel.GEMINI_2_0_FLASH)
+			.toolCallbacks(List.of(FunctionToolCallback.builder("get_current_weather", new MockWeatherService())
+				.description("Get the current weather in a given location.")
+				.inputType(MockWeatherService.Request.class)
+				.build()))
+			.build();
+
+		ChatResponse chatResponse = this.chatModel.call(new Prompt(messages, promptOptions));
+
+		assertThat(chatResponse.getResult().getOutput().getText()).contains("30", "10", "15");
+
+		assertThat(chatResponse.getMetadata()).isNotNull();
+		assertThat(chatResponse.getMetadata().getUsage()).isNotNull();
+		assertThat(chatResponse.getMetadata().getUsage().getTotalTokens()).isGreaterThan(150).isLessThan(550);
+	}
+
 	@Test
 	public void functionCallTestInferredOpenApiSchema() {