Fail at build time when tools set and no memory provided

core/deployment/src/main/java/io/quarkiverse/langchain4j/deployment/AiServicesProcessor.java

@@ -170,7 +170,17 @@ public void findDeclarativeServices(CombinedIndexBuildItem indexBuildItem,
                 needChatModelBean = true;
             }
 
-            DotName chatMemoryProviderSupplierClassDotName = Langchain4jDotNames.BEAN_IF_EXISTS_CHAT_MEMORY_PROVIDER_SUPPLIER;
+            List<DotName> toolDotNames = Collections.emptyList();
+            AnnotationValue toolsInstance = instance.value("tools");
+            if (toolsInstance != null) {
+                toolDotNames = Arrays.stream(toolsInstance.asClassArray()).map(Type::name)
+                        .collect(Collectors.toList());
+            }
+
+            // the default value depends on whether tools exists or not - if they do, then we require a ChatMemoryProvider bean
+            DotName chatMemoryProviderSupplierClassDotName = toolDotNames.isEmpty()
+                    ? Langchain4jDotNames.BEAN_IF_EXISTS_CHAT_MEMORY_PROVIDER_SUPPLIER
+                    : Langchain4jDotNames.BEAN_CHAT_MEMORY_PROVIDER_SUPPLIER;
             AnnotationValue chatMemoryProviderSupplierValue = instance.value("chatMemoryProviderSupplier");
             if (chatMemoryProviderSupplierValue != null) {
                 chatMemoryProviderSupplierClassDotName = chatMemoryProviderSupplierValue.asClass().name();
@@ -184,18 +194,6 @@ public void findDeclarativeServices(CombinedIndexBuildItem indexBuildItem,
                 }
             }
 
-            List<DotName> toolDotNames = Collections.emptyList();
-            AnnotationValue toolsInstance = instance.value("tools");
-            if (toolsInstance != null) {
-                if (chatMemoryProviderSupplierClassDotName == null) {
-                    throw new IllegalConfigurationException("Class '" + declarativeAiServiceClassInfo.name()
-                            + "' which is annotated with @RegisterAiService has configured tools support, but no ChatMemoryProvider configuration is present. Please set up chatMemoryProvider in order to use tools. A ChatMemory that can hold at least 3 messages is required for the tools to work properly. While the LLM can technically execute a tool without chat memory, if it only receives the result of the tool's execution without the initial message from the user, it won't interpret the result properly.");
-                }
-
-                toolDotNames = Arrays.stream(toolsInstance.asClassArray()).map(Type::name)
-                        .collect(Collectors.toList());
-            }
-
             DotName retrieverSupplierClassDotName = Langchain4jDotNames.BEAN_IF_EXISTS_RETRIEVER_SUPPLIER;
             AnnotationValue retrieverSupplierValue = instance.value("retrieverSupplier");
             if (retrieverSupplierValue != null) {

core/runtime/src/main/java/io/quarkiverse/langchain4j/RegisterAiService.java

@@ -44,7 +44,8 @@
     /**
      * Tool classes to use. All tools are expected to be CDI beans.
      * <p>
-     * NOTE: when this is used, {@code chatMemoryProviderSupplier} must NOT be set to {@link NoChatMemoryProviderSupplier}.
+     * NOTE: when this is used, either a {@link ChatMemoryProvider} bean must be present in the application, or a custom
+     * {@link Supplier<ChatMemoryProvider>} must be set.
      */
     Class<?>[] tools() default {};
 
@@ -57,6 +58,10 @@
      * <p>
      * If the memory provider to use is exposed as a CDI bean exposing the type {@link ChatMemoryProvider}, then
      * set the value to {@link RegisterAiService.BeanChatMemoryProviderSupplier}
+     * <p>
+     * NOTE: when {@link tools} is set, the default is changed to {@link BeanChatMemoryProviderSupplier} which means that a
+     * bean a {@link ChatMemoryProvider} bean must be present. The alternative in this case is to set a custom
+     * {@link Supplier<ChatMemoryProvider>}.
      */
     Class<? extends Supplier<ChatMemoryProvider>> chatMemoryProviderSupplier() default BeanIfExistsChatMemoryProviderSupplier.class;
 

openai/openai-vanilla/deployment/src/test/java/io/quarkiverse/langchain4j/openai/test/AiServiceWithToolsAndNoMemoryTest.java

@@ -0,0 +1,52 @@
+package io.quarkiverse.langchain4j.openai.test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.fail;
+
+import jakarta.enterprise.inject.spi.DeploymentException;
+import jakarta.inject.Inject;
+import jakarta.inject.Singleton;
+
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import dev.langchain4j.agent.tool.Tool;
+import io.quarkiverse.langchain4j.RegisterAiService;
+import io.quarkus.test.QuarkusUnitTest;
+
+public class AiServiceWithToolsAndNoMemoryTest {
+
+    @RegisterExtension
+    static final QuarkusUnitTest unitTest = new QuarkusUnitTest()
+            .setArchiveProducer(() -> ShrinkWrap.create(JavaArchive.class).addClasses())
+            .assertException(t -> {
+                assertThat(t)
+                        .isInstanceOf(DeploymentException.class)
+                        .hasMessageContaining("ChatMemoryProvider");
+            });
+
+    @RegisterAiService(tools = CustomTool.class)
+    interface Assistant {
+
+        String chat(String input);
+    }
+
+    @Singleton
+    static class CustomTool {
+
+        @Tool
+        void doSomething() {
+
+        }
+    }
+
+    @Inject
+    Assistant assistant;
+
+    @Test
+    void test() {
+        fail("Should not be called");
+    }
+}