GH-4596: Handle candidates containing both text and tool calls in VertexAiGeminiChatModel

Fix #4596

Auto-cherry-pick to 1.0.x

Signed-off-by: NathanGrand <nathangrand@quantexa.com>
Signed-off-by: Eric Bottard <eric.bottard@broadcom.com>

Author: q-nathangrand

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;
@@ -600,39 +601,27 @@ protected List<Generation> responseCandidateToGeneration(Candidate candidate) {
 			.finishReason(candidateFinishReason.name())
 			.build();
 
-		boolean isFunctionCall = candidate.getContent().getPartsList().stream().allMatch(Part::hasFunctionCall);
+		List<Part> parts = candidate.getContent().getPartsList();
 
-		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();
+		List<AssistantMessage.ToolCall> assistantToolCalls = parts.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 = AssistantMessage.builder()
-				.content("")
-				.properties(messageMetadata)
-				.toolCalls(assistantToolCalls)
-				.build();
+		String text = parts.stream()
+			.filter(part -> part.hasText() && !part.getText().isEmpty())
+			.map(Part::getText)
+			.collect(Collectors.joining(" "));
 
-			return List.of(new Generation(assistantMessage, chatGenerationMetadata));
-		}
-		else {
-			List<Generation> generations = candidate.getContent()
-				.getPartsList()
-				.stream()
-				.map(part -> AssistantMessage.builder().content(part.getText()).properties(messageMetadata).build())
-				.map(assistantMessage -> new Generation(assistantMessage, chatGenerationMetadata))
-				.toList();
+		AssistantMessage assistantMessage = AssistantMessage.builder()
+			.content(text)
+			.properties(messageMetadata)
+			.toolCalls(assistantToolCalls)
+			.build();
 
-			return generations;
-		}
+		return List.of(new Generation(assistantMessage, chatGenerationMetadata));
 	}
 
 	private ChatResponseMetadata toChatResponseMetadata(Usage usage) {

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

@@ -414,6 +414,47 @@ void jsonTextToolCallingTest() {
 		assertThat(response).contains("2025-05-08T10:10:10+02:00[Europe/Berlin]");
 	}
 
+	/**
+	 * See https://github.com/spring-projects/spring-ai/pull/4599
+	 */
+	@Test
+	void testMixedPartsMessages() {
+		VertexAiGeminiChatModel chatModelWithTools = VertexAiGeminiChatModel.builder()
+			.vertexAI(vertexAiApi())
+			.defaultOptions(VertexAiGeminiChatOptions.builder().model("gemini-2.5-pro").temperature(0.0).build())
+			.build();
+
+		ChatClient chatClient = ChatClient.builder(chatModelWithTools).build();
+
+		// Create a prompt that will encourage gemini to explain why it is calling tools
+		// as it does.
+		AlarmTools alarmTools = new AlarmTools();
+		String response = chatClient.prompt()
+			.tools(new CurrentTimeTools(), alarmTools)
+			.system("You MUST include reasoning when you issue tool calls.")
+			.user("Set an alarm for an hour from now, and tell me what time that was for.")
+			.call()
+			.content();
+
+		assertThat(response).isEqualTo("I have set an alarm for 11:10 AM.");
+		assertThat(alarmTools.getAlarm()).isEqualTo("2025-05-08T11:10:10+02:00");
+	}
+
+	public static class AlarmTools {
+
+		private String alarm;
+
+		@Tool(description = "Set a user alarm for the given time, provided in ISO-8601 format")
+		void setAlarm(String time) {
+			this.alarm = time;
+		}
+
+		public String getAlarm() {
+			return this.alarm;
+		}
+
+	}
+
 	/**
 	 * Tool class that returns a JSON array to test the jsonToStruct method's ability to
 	 * handle JSON arrays. This specifically tests the PR changes that improve the