Introduce TestRuntimeHintsRegistrar in the TestContext framework

Although RuntimeHintsRegistrar can be implemented to register general
hints that should be applied for all testing infrastructure, certain
use cases require access to test classes and the
MergedContextConfiguration in order to register appropriate hints.

To address that, this commit introduces TestRuntimeHintsRegistrar as a
companion to the core RuntimeHintsRegistrar.

Closes gh-29069

spring-test/src/main/java/org/springframework/test/context/aot/TestContextAotGenerator.java

@@ -17,6 +17,7 @@
 package org.springframework.test.context.aot;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Stream;
 
@@ -31,6 +32,7 @@ import org.springframework.aot.generate.GenerationContext;
 import org.springframework.aot.hint.ReflectionHints;
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.TypeReference;
+import org.springframework.beans.factory.aot.AotServices;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.aot.ApplicationContextAotGenerator;
@@ -67,6 +69,8 @@ public class TestContextAotGenerator {
 
 	private final ApplicationContextAotGenerator aotGenerator = new ApplicationContextAotGenerator();
 
+	private final AotServices<TestRuntimeHintsRegistrar> testRuntimeHintsRegistrars;
+
 	private final AtomicInteger sequence = new AtomicInteger();
 
 	private final GeneratedFiles generatedFiles;
@@ -90,6 +94,7 @@ public class TestContextAotGenerator {
 	 * @param runtimeHints the {@code RuntimeHints} to use
 	 */
 	public TestContextAotGenerator(GeneratedFiles generatedFiles, RuntimeHints runtimeHints) {
+		this.testRuntimeHintsRegistrars = AotServices.factories().load(TestRuntimeHintsRegistrar.class);
 		this.generatedFiles = generatedFiles;
 		this.runtimeHints = runtimeHints;
 	}
@@ -121,6 +126,9 @@ public class TestContextAotGenerator {
 					testClasses.stream().map(Class::getName).toList()));
 			registerHintsForMergedConfig(mergedConfig);
 			try {
+				this.testRuntimeHintsRegistrars.forEach(registrar -> registrar.registerHints(this.runtimeHints,
+						mergedConfig, Collections.unmodifiableList(testClasses), getClass().getClassLoader()));
+
 				// Use first test class discovered for a given unique MergedContextConfiguration.
 				Class<?> testClass = testClasses.get(0);
 				DefaultGenerationContext generationContext = createGenerationContext(testClass);

spring-test/src/main/java/org/springframework/test/context/aot/TestRuntimeHintsRegistrar.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2002-2022 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.test.context.aot;
+
+import java.util.List;
+
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.test.context.MergedContextConfiguration;
+
+/**
+ * Contract for registering {@link RuntimeHints} for integration tests run with
+ * the <em>Spring TestContext Framework</em> based on the {@link ClassLoader}
+ * of the deployment unit. Implementations should, if possible, use the specified
+ * {@link ClassLoader} to determine if hints have to be contributed.
+ *
+ * <p>Implementations of this interface must be registered statically in
+ * {@code META-INF/spring/aot.factories} by using the fully qualified name of this
+ * interface as the key. A standard no-arg constructor is required for implementations.
+ *
+ * <p>This API serves as a companion to the core
+ * {@link org.springframework.aot.hint.RuntimeHintsRegistrar RuntimeHintsRegistrar}
+ * API. If you need to register global hints for testing support that are not
+ * specific to a particular test class or {@link MergedContextConfiguration}, favor
+ * implementing {@code RuntimeHintsRegistrar} over this API.
+ *
+ * @author Sam Brannen
+ * @since 6.0
+ * @see org.springframework.aot.hint.RuntimeHintsRegistrar
+ */
+public interface TestRuntimeHintsRegistrar {
+
+	/**
+	 * Contribute hints to the given {@link RuntimeHints} instance.
+	 * @param runtimeHints the {@code RuntimeHints} to use
+	 * @param mergedConfig the merged context configuration to process
+	 * @param testClasses the test classes that share the supplied merged context
+	 * configuration
+	 * @param classLoader the classloader to use
+	 */
+	void registerHints(RuntimeHints runtimeHints, MergedContextConfiguration mergedConfig,
+			List<Class<?>> testClasses, ClassLoader classLoader);
+
+}