feat: Improve local subscriptions

backend/controller/pubsub/testdata/java/publisher/src/main/java/xyz/block/ftl/java/test/publisher/Publisher.java

@@ -4,6 +4,7 @@
 import xyz.block.ftl.Export;
 import xyz.block.ftl.Topic;
 import xyz.block.ftl.TopicDefinition;
+import xyz.block.ftl.Subscription;
 import xyz.block.ftl.Verb;
 
 public class Publisher {
@@ -14,14 +15,19 @@ interface TestTopic extends Topic<PubSubEvent> {
 
     }
 
+    @TopicDefinition("localTopic")
+    interface LocalTopic extends Topic<PubSubEvent> {
+
+    }
+
     @Export
     @TopicDefinition("topic2")
     interface Topic2 extends Topic<PubSubEvent> {
 
     }
 
     @Verb
-    void publishTen(TestTopic testTopic) throws Exception {
+    void publishTen(LocalTopic testTopic) throws Exception {
         for (var i = 0; i < 10; ++i) {
             var t = java.time.ZonedDateTime.now();
             Log.infof("Publishing %s", t);
@@ -42,4 +48,9 @@ void publishOneToTopic2(Topic2 topic2) throws Exception {
         Log.infof("Publishing %s", t);
         topic2.publish(new PubSubEvent().setTime(t));
     }
+
+    @Subscription(topicClass = LocalTopic.class, name = "localSubscription")
+    public void local(TestTopic testTopic, PubSubEvent event) {
+        testTopic.publish(event);
+    }
 }

docs/content/docs/reference/pubsub.md

@@ -116,14 +116,13 @@ There are two ways to subscribe to a topic. The first is to declare a method wit
 subscribing to a topic inside the same module:
 
 ```java
-@Subscription(topic = "invoices", name = "invoicesSubscription")
+@Subscription(topicClass = InvoiceTopic.class, name = "invoicesSubscription")
 public void consumeInvoice(Invoice event) {
     // ...
 }
 ```
 
-This is ok, but it requires the use of string constants for the topic name, which can be error-prone. If you are subscribing to a topic from
-another module, FTL will generate a type-safe subscription meta annotation you can use to subscribe to the topic:
+If you are subscribing to a topic from another module, FTL will generate a type-safe subscription meta annotation you can use to subscribe to the topic:
 
 ```java
 @Retention(java.lang.annotation.RetentionPolicy.RUNTIME)

jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/FTLDotNames.java

@@ -8,6 +8,7 @@
 import xyz.block.ftl.LeaseClient;
 import xyz.block.ftl.Secret;
 import xyz.block.ftl.Subscription;
+import xyz.block.ftl.TopicDefinition;
 import xyz.block.ftl.TypeAlias;
 import xyz.block.ftl.TypeAliasMapper;
 import xyz.block.ftl.Verb;
@@ -27,4 +28,5 @@ private FTLDotNames() {
     public static final DotName TYPE_ALIAS = DotName.createSimple(TypeAlias.class);
     public static final DotName SUBSCRIPTION = DotName.createSimple(Subscription.class);
     public static final DotName LEASE_CLIENT = DotName.createSimple(LeaseClient.class);
+    public static final DotName TOPIC_DEFINITION = DotName.createSimple(TopicDefinition.class);
 }

jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/SubscriptionMetaAnnotationsBuildItem.java

@@ -5,8 +5,10 @@
 import org.jboss.jandex.AnnotationInstance;
 import org.jboss.jandex.AnnotationValue;
 import org.jboss.jandex.DotName;
+import org.jboss.jandex.IndexView;
 
 import io.quarkus.builder.item.SimpleBuildItem;
+import xyz.block.ftl.Topic;
 
 public final class SubscriptionMetaAnnotationsBuildItem extends SimpleBuildItem {
 
@@ -23,13 +25,33 @@ public Map<DotName, SubscriptionAnnotation> getAnnotations() {
     public record SubscriptionAnnotation(String module, String topic, String name) {
     }
 
-    public static SubscriptionAnnotation fromJandex(AnnotationInstance subscriptions, String currentModuleName) {
-        AnnotationValue moduleValue = subscriptions.value("module");
+    public static SubscriptionAnnotation fromJandex(IndexView indexView, AnnotationInstance subscriptions,
+            String currentModuleName) {
 
+        AnnotationValue moduleValue = subscriptions.value("module");
+        AnnotationValue topicValue = subscriptions.value("topic");
+        AnnotationValue topicClassValue = subscriptions.value("topicClass");
+        String topicName;
+        if (topicValue != null && !topicValue.asString().isEmpty()) {
+            if (topicClassValue != null && !topicClassValue.asClass().name().toString().equals(Topic.class.getName())) {
+                throw new IllegalArgumentException("Cannot specify both topic and topicClass");
+            }
+            topicName = topicValue.asString();
+        } else if (topicClassValue != null && !topicClassValue.asClass().name().toString().equals(Topic.class.getName())) {
+            var topicClass = indexView.getClassByName(topicClassValue.asClass().name());
+            AnnotationInstance annotation = topicClass.annotation(FTLDotNames.TOPIC_DEFINITION);
+            if (annotation == null) {
+                throw new IllegalArgumentException(
+                        "topicClass must be annotated with @TopicDefinition for subscription " + subscriptions);
+            }
+            topicName = annotation.value().asString();
+        } else {
+            throw new IllegalArgumentException("Either topic or topicClass must be specified on " + subscriptions);
+        }
         return new SubscriptionMetaAnnotationsBuildItem.SubscriptionAnnotation(
                 moduleValue == null || moduleValue.asString().isEmpty() ? currentModuleName
                         : moduleValue.asString(),
-                subscriptions.value("topic").asString(),
+                topicName,
                 subscriptions.value("name").asString());
     }
 }

jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/SubscriptionProcessor.java

@@ -33,7 +33,8 @@ SubscriptionMetaAnnotationsBuildItem subscriptionAnnotations(CombinedIndexBuildI
                 continue;
             }
             annotations.put(subscriptions.target().asClass().name(),
-                    SubscriptionMetaAnnotationsBuildItem.fromJandex(subscriptions, moduleNameBuildItem.getModuleName()));
+                    SubscriptionMetaAnnotationsBuildItem.fromJandex(combinedIndexBuildItem.getComputingIndex(), subscriptions,
+                            moduleNameBuildItem.getModuleName()));
         }
         return new SubscriptionMetaAnnotationsBuildItem(annotations);
     }
@@ -47,7 +48,7 @@ public void registerSubscriptions(CombinedIndexBuildItem index,
         AdditionalBeanBuildItem.Builder beans = AdditionalBeanBuildItem.builder().setUnremovable();
         var moduleName = moduleNameBuildItem.getModuleName();
         for (var subscription : index.getIndex().getAnnotations(FTLDotNames.SUBSCRIPTION)) {
-            var info = SubscriptionMetaAnnotationsBuildItem.fromJandex(subscription, moduleName);
+            var info = SubscriptionMetaAnnotationsBuildItem.fromJandex(index.getComputingIndex(), subscription, moduleName);
             if (subscription.target().kind() != AnnotationTarget.Kind.METHOD) {
                 continue;
             }

jvm-runtime/ftl-runtime/common/deployment/src/main/java/xyz/block/ftl/deployment/TopicsProcessor.java

@@ -18,7 +18,6 @@
 import io.quarkus.gizmo.MethodDescriptor;
 import xyz.block.ftl.Export;
 import xyz.block.ftl.Topic;
-import xyz.block.ftl.TopicDefinition;
 import xyz.block.ftl.runtime.TopicHelper;
 import xyz.block.ftl.v1.schema.Decl;
 
@@ -28,7 +27,7 @@ public class TopicsProcessor {
 
     @BuildStep
     TopicsBuildItem handleTopics(CombinedIndexBuildItem index, BuildProducer<GeneratedClassBuildItem> generatedTopicProducer) {
-        var topicDefinitions = index.getComputingIndex().getAnnotations(TopicDefinition.class);
+        var topicDefinitions = index.getComputingIndex().getAnnotations(FTLDotNames.TOPIC_DEFINITION);
         Map<DotName, TopicsBuildItem.DiscoveredTopic> topics = new HashMap<>();
         Set<String> names = new HashSet<>();
         for (var topicDefinition : topicDefinitions) {

jvm-runtime/ftl-runtime/common/runtime/src/main/java/xyz/block/ftl/Subscription.java

@@ -15,14 +15,18 @@
 
     /**
      *
-     * @return The name of the topic to subscribe to.
+     * @return The name of the topic to subscribe to. Cannot be used in conjunction with {@link #topicClass()}.
      */
-    String topic();
+    String topic() default "";
 
     /**
      *
      * @return The subscription name
      */
     String name();
 
+    /**
+     * The class of the topic to subscribe to, which can be used in place of directly specifying the topic name and module.
+     */
+    Class<? extends Topic> topicClass() default Topic.class;
 }