Fix Gateway proxy registration for AOT

The `GatewayProxyInstantiationPostProcessor` does nothing on the AOT phase.
Therefore, scanned and imported beans for `@MessagingGateway` are not decorated
after AOT

* Implement a `BeanRegistrationAotProcessor` in the `GatewayProxyInstantiationPostProcessor`
to `RegisteredBean.getMergedBeanDefinition()` withe respective `AnnotationGatewayProxyFactoryBean`
and its requirements for ctor arg and `targetType`
* Scan for the `@MessagingGateway` bean in the `GatewayProxyInitializationAotProcessor`
to register respective proxy hints

spring-integration-core/src/main/java/org/springframework/integration/aot/GatewayProxyInitializationAotProcessor.java

@@ -18,6 +18,7 @@ package org.springframework.integration.aot;
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.stream.Stream;
 
 import org.springframework.aop.framework.AopProxyUtils;
 import org.springframework.aop.framework.ProxyFactoryBean;
@@ -26,12 +27,15 @@ import org.springframework.beans.factory.aot.BeanFactoryInitializationAotContrib
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.support.RegisteredBean;
+import org.springframework.core.annotation.AnnotatedElementUtils;
+import org.springframework.integration.annotation.MessagingGateway;
 import org.springframework.integration.gateway.GatewayProxyFactoryBean;
 import org.springframework.integration.gateway.RequestReplyExchanger;
 
+
 /**
  * A {@link BeanFactoryInitializationAotProcessor} for registering proxy interfaces
- * of the {@link GatewayProxyFactoryBean} beans.
+ * of the {@link GatewayProxyFactoryBean} beans or {@link MessagingGateway} interfaces.
  *
  * @author Artem Bilan
  *
@@ -41,13 +45,23 @@ class GatewayProxyInitializationAotProcessor implements BeanFactoryInitializatio
 
 	@Override
 	public BeanFactoryInitializationAotContribution processAheadOfTime(ConfigurableListableBeanFactory beanFactory) {
-		List<? extends Class<?>> gatewayProxyInterfaces =
+		List<RegisteredBean> registeredBeans =
 				Arrays.stream(beanFactory.getBeanDefinitionNames())
 						.map((beanName) -> RegisteredBean.of(beanFactory, beanName))
-						.filter((bean) -> ProxyFactoryBean.class.isAssignableFrom(bean.getBeanClass()))
-						.map((bean) -> bean.getBeanType().getGeneric(0).resolve(RequestReplyExchanger.class))
 						.toList();
 
+		Stream<Class<?>> gatewayProxyInterfaces =
+				Stream.concat(
+						registeredBeans.stream()
+								.filter(bean -> ProxyFactoryBean.class.isAssignableFrom(bean.getBeanClass()))
+								.map((bean) ->
+										bean.getBeanType().getGeneric(0).resolve(RequestReplyExchanger.class)),
+						registeredBeans.stream()
+								.map(RegisteredBean::getBeanClass)
+								.filter(beanClass ->
+										beanClass.isInterface() &&
+												AnnotatedElementUtils.hasAnnotation(beanClass, MessagingGateway.class)));
+
 		return (generationContext, beanFactoryInitializationCode) -> {
 			ProxyHints proxyHints = generationContext.getRuntimeHints().proxies();
 			gatewayProxyInterfaces.forEach((gatewayInterface) ->

spring-integration-core/src/main/java/org/springframework/integration/config/GatewayProxyInstantiationPostProcessor.java

@@ -18,12 +18,17 @@ package org.springframework.integration.config;
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.annotation.AnnotatedGenericBeanDefinition;
+import org.springframework.beans.factory.aot.BeanRegistrationAotContribution;
+import org.springframework.beans.factory.aot.BeanRegistrationAotProcessor;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
+import org.springframework.beans.factory.support.RegisteredBean;
+import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
 import org.springframework.context.annotation.ScannedGenericBeanDefinition;
+import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.integration.annotation.MessagingGateway;
 import org.springframework.integration.gateway.AnnotationGatewayProxyFactoryBean;
@@ -39,7 +44,7 @@ import org.springframework.integration.gateway.AnnotationGatewayProxyFactoryBean
  * @see AnnotationGatewayProxyFactoryBean
  */
 class GatewayProxyInstantiationPostProcessor implements
-		InstantiationAwareBeanPostProcessor, ApplicationContextAware {
+		InstantiationAwareBeanPostProcessor, BeanRegistrationAotProcessor, ApplicationContextAware {
 
 	private final BeanDefinitionRegistry registry;
 
@@ -77,4 +82,17 @@ class GatewayProxyInstantiationPostProcessor implements
 		return null;
 	}
 
+	@Override
+	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
+		Class<?> beanClass = registeredBean.getBeanClass();
+		if (beanClass.isInterface() && AnnotatedElementUtils.hasAnnotation(beanClass, MessagingGateway.class)) {
+			RootBeanDefinition beanDefinition = registeredBean.getMergedBeanDefinition();
+			beanDefinition.setBeanClass(AnnotationGatewayProxyFactoryBean.class);
+			beanDefinition.getConstructorArgumentValues().addGenericArgumentValue(beanClass);
+			beanDefinition.setTargetType(
+					ResolvableType.forClassWithGenerics(AnnotationGatewayProxyFactoryBean.class, beanClass));
+		}
+		return null;
+	}
+
 }