#1983 - Additional reflection hints for custom Jackson serializer in EntityModel.

We now register reflection hints for all types contained in EntityModel, so that MapSuppressingUnwrappingSerializer's default constructor can be called from Jackson.

Original ticket: #1981
Related ticket: spring-projects/spring-boot#36057

src/main/java/org/springframework/hateoas/aot/RepresentationModelRuntimeHints.java

@@ -15,10 +15,11 @@
  */
 package org.springframework.hateoas.aot;
 
+import java.util.Arrays;
 import java.util.List;
+import java.util.stream.Stream;
 
 import org.springframework.aot.hint.MemberCategory;
-import org.springframework.aot.hint.ReflectionHints;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.hateoas.CollectionModel;
@@ -34,7 +35,7 @@ import org.springframework.hateoas.RepresentationModel;
 class RepresentationModelRuntimeHints implements RuntimeHintsRegistrar {
 
 	private static final List<Class<?>> REPRESENTATION_MODELS = List.of(RepresentationModel.class, //
-			EntityModel.class, //
+			// EntityModel.class, // treated specially below
 			CollectionModel.class, //
 			PagedModel.class,
 			PagedModel.PageMetadata.class);
@@ -46,9 +47,12 @@ class RepresentationModelRuntimeHints implements RuntimeHintsRegistrar {
 	@Override
 	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
 
-		ReflectionHints reflection = hints.reflection();
+		var reflection = hints.reflection();
+		var entityModelAndNested = Arrays.stream(EntityModel.class.getNestMembers());
 
-		REPRESENTATION_MODELS.forEach(it -> reflection.registerType(it, //
-				MemberCategory.INVOKE_DECLARED_CONSTRUCTORS, MemberCategory.INVOKE_DECLARED_METHODS));
+		Stream.concat(REPRESENTATION_MODELS.stream(), entityModelAndNested).forEach(it -> { //
+			reflection.registerType(it, //
+					MemberCategory.INVOKE_DECLARED_CONSTRUCTORS, MemberCategory.INVOKE_DECLARED_METHODS);
+		});
 	}
 }

src/test/java/org/springframework/hateoas/aot/RepresentationModelRuntimeHintsUnitTests.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.hateoas.aot;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.TypeHint;
+import org.springframework.aot.hint.TypeReference;
+
+/**
+ * Unit tests for {@link RepresentationModelRuntimeHints}.
+ *
+ * @author Oliver Drotbohm
+ */
+class RepresentationModelRuntimeHintsUnitTests {
+
+	@Test // GH-1981
+	void registersHintsForMapSuppressingUnwrappingSerializer() {
+
+		var registrar = new RepresentationModelRuntimeHints();
+		var hints = new RuntimeHints();
+
+		registrar.registerHints(hints, getClass().getClassLoader());
+
+		assertThat(hints.reflection().typeHints())
+				.extracting(TypeHint::getType)
+				.extracting(TypeReference::getSimpleName)
+				.contains("MapSuppressingUnwrappingSerializer");
+	}
+}