Fix #5470: exclude duplicate query from history in CompressionQueryTransformer

spring-ai-rag/src/main/java/org/springframework/ai/rag/preretrieval/query/transformation/CompressionQueryTransformer.java

@@ -77,11 +77,29 @@ public CompressionQueryTransformer(ChatClient.Builder chatClientBuilder, @Nullab
 	public Query transform(Query query) {
 		Assert.notNull(query, "query cannot be null");
 
+		if (query.history().isEmpty()) {
+			logger.debug("No conversation history to compress. Returning the original query.");
+			return query;
+		}
+
 		logger.debug("Compressing conversation history and follow-up query into a standalone query");
 
+		// Exclude the last history entry if it's a duplicate of the current query
+		List<Message> history = query.history();
+		List<Message> effectiveHistory;
+		int lastIdx = history.size() - 1;
+		Message lastMessage = history.get(lastIdx);
+		String lastText = lastMessage.getText();
+		if (lastMessage.getMessageType() == MessageType.USER && lastText != null && lastText.equals(query.text())) {
+			effectiveHistory = history.subList(0, lastIdx);
+		}
+		else {
+			effectiveHistory = history;
+		}
+
 		var compressedQueryText = this.chatClient.prompt()
 			.user(user -> user.text(this.promptTemplate.getTemplate())
-				.param("history", formatConversationHistory(query.history()))
+				.param("history", formatConversationHistory(effectiveHistory))
 				.param("query", query.text()))
 			.call()
 			.content();
@@ -136,4 +154,4 @@ public CompressionQueryTransformer build() {
 
 	}
 
-}
+}

spring-ai-rag/src/test/java/org/springframework/ai/rag/preretrieval/query/transformation/CompressionQueryTransformerTests.java

@@ -19,10 +19,16 @@
 import org.junit.jupiter.api.Test;
 
 import org.springframework.ai.chat.client.ChatClient;
+import org.springframework.ai.chat.messages.Message;
+import org.springframework.ai.chat.messages.MessageType;
 import org.springframework.ai.chat.prompt.PromptTemplate;
+import org.springframework.ai.rag.Query;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 
 /**
  * Unit tests for {@link CompressionQueryTransformer}.
@@ -69,4 +75,55 @@ void whenPromptHasMissingQueryPlaceholderThenThrow() {
 			.hasMessageContaining("query");
 	}
 
+	@Test
+	void whenHistoryIsEmptyThenReturnOriginalQuery() {
+		ChatClient.Builder chatClientBuilder = mock(ChatClient.Builder.class);
+		ChatClient chatClient = mock(ChatClient.class);
+		when(chatClientBuilder.build()).thenReturn(chatClient);
+
+		QueryTransformer queryTransformer = CompressionQueryTransformer.builder()
+			.chatClientBuilder(chatClientBuilder)
+			.build();
+
+		Query query = Query.builder().text("What is Spring AI?").build();
+
+		Query result = queryTransformer.transform(query);
+
+		assertThat(result).isEqualTo(query);
+	}
+
+	@Test
+	void whenLastHistoryEntryMatchesCurrentQueryThenExcludeItFromHistory() {
+		ChatClient.Builder chatClientBuilder = mock(ChatClient.Builder.class);
+		ChatClient chatClient = mock(ChatClient.class);
+		ChatClient.Callable mockedCallable = mock(ChatClient.Callable.class);
+		when(chatClientBuilder.build()).thenReturn(chatClient);
+		when(chatClient.prompt()).thenReturn(mockedCallable);
+		when(mockedCallable.user(any())).thenReturn(mockedCallable);
+		when(mockedCallable.call()).thenReturn(
+				org.springframework.ai.chat.client.ChatResponse.builder().content("What is Spring AI?").build());
+
+		QueryTransformer queryTransformer = CompressionQueryTransformer.builder()
+			.chatClientBuilder(chatClientBuilder)
+			.build();
+
+		String currentQueryText = "What is Spring AI?";
+		Message userMessage = Message.builder().messageType(MessageType.USER).text(currentQueryText).build();
+		Message assistantMessage = Message.builder()
+			.messageType(MessageType.ASSISTANT)
+			.text("Spring AI is a framework for AI-native applications.")
+			.build();
+
+		Query query = Query.builder()
+			.text(currentQueryText)
+			.history(java.util.List.of(assistantMessage, userMessage))
+			.build();
+
+		queryTransformer.transform(query);
+
+		// Verify the prompt was called - the history should not contain the duplicate
+		// query
+		verify(chatClient).prompt();
+	}
+
 }