Fix AOT code generation for managed types.

Closes #2704
Original pull request: #2705.

Author: christophstrobl

src/main/java/org/springframework/data/aot/ManagedTypesRegistrationAotContribution.java

@@ -17,6 +17,7 @@
 
 import java.lang.reflect.Executable;
 import java.lang.reflect.Method;
+import java.util.Collections;
 import java.util.List;
 import java.util.function.BiConsumer;
 
@@ -34,9 +35,12 @@
 import org.springframework.core.ResolvableType;
 import org.springframework.data.domain.ManagedTypes;
 import org.springframework.data.util.Lazy;
+import org.springframework.javapoet.ClassName;
 import org.springframework.javapoet.CodeBlock;
 import org.springframework.javapoet.MethodSpec.Builder;
 import org.springframework.javapoet.ParameterizedTypeName;
+import org.springframework.javapoet.TypeName;
+import org.springframework.javapoet.WildcardTypeName;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
@@ -167,7 +171,15 @@ void generateInstanceFactory(Builder method) {
 
 			CodeBlock.Builder builder = CodeBlock.builder().add("return ").beginControlFlow("(registeredBean -> ");
 
-			builder.addStatement("var types = $T.of($L)", List.class, toCodeBlock(sourceTypes, allSourceTypesVisible));
+			if(sourceTypes.isEmpty()) {
+
+				TypeName wildcard = WildcardTypeName.subtypeOf(Object.class);
+				TypeName classOfAny = ParameterizedTypeName.get(ClassName.get(Class.class), wildcard);
+
+				builder.addStatement("var types = $T.<$T>emptyList()", Collections.class, classOfAny);
+			} else {
+				builder.addStatement("var types = $T.of($L)", List.class, toCodeBlock(sourceTypes, allSourceTypesVisible));
+			}
 
 			if (allSourceTypesVisible) {
 				builder.addStatement("var managedTypes = $T.fromIterable($L)", ManagedTypes.class, "types");

src/test/java/org/springframework/data/aot/ManagedTypesBeanRegistrationAotProcessorUnitTests.java

@@ -195,6 +195,28 @@ void generatesInstanceSupplierCodeFragmentToAvoidDuplicateInvocations() {
 		});
 	}
 
+	@Test // GH-2680
+	void generatesInstanceSupplierCodeFragmentToAvoidDuplicateInvocationsForEmptyManagedTypes() {
+
+		beanFactory.registerBeanDefinition("commons.managed-types", BeanDefinitionBuilder.rootBeanDefinition(EmptyManagedTypes.class).getBeanDefinition());
+		RegisteredBean registeredBean = RegisteredBean.of(beanFactory, "commons.managed-types");
+
+		BeanRegistrationAotContribution contribution = createPostProcessor("commons")
+				.processAheadOfTime(RegisteredBean.of(beanFactory, "commons.managed-types"));
+
+		AotTestCodeContributionBuilder.withContextFor(this.getClass()).writeContentFor(contribution).compile(it -> {
+
+
+			InstanceSupplier<ManagedTypes> types = ReflectionTestUtils
+					.invokeMethod(it.getAllCompiledClasses().iterator().next(), "instance");
+			try {
+				assertThat(types.get(registeredBean).toList()).isEmpty();
+			} catch (Exception e) {
+				throw new RuntimeException(e);
+			}
+		});
+	}
+
 	@Test // GH-2680
 	void generatesInstanceSupplierCodeFragmentForTypeWithCustomFactoryMethod() {
 
@@ -269,6 +291,22 @@ public void forEach(Consumer<Class<?>> action) {
 		}
 	}
 
+	public static class EmptyManagedTypes implements ManagedTypes {
+
+		public EmptyManagedTypes() {
+
+		}
+
+		public static EmptyManagedTypes of(ManagedTypes source) {
+			return new EmptyManagedTypes();
+		}
+
+		@Override
+		public void forEach(Consumer<Class<?>> action) {
+
+		}
+	}
+
 	public static class StoreManagedTypesWithCustomFactoryMethod implements ManagedTypes {
 
 		private ManagedTypes source;