Update SpringBootContextLoader to support AOT

Update `SpringBootContextLoader` so that it now implements the
`AotContextLoader` interface. The `ContextLoaderHook` will abandon
at `contextLoaded` if the test class is being AOT processed.

This commit also introduces a new `AotApplicationContextInitializer`
which allows us to plug-in an alternative AOT application context
listener when the `SpringApplication` is running in test mode.

Closes gh-31965

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/SpringBootContextLoaderAotTests.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2012-2022 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.boot.test.context;
+
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.AotDetector;
+import org.springframework.aot.generate.InMemoryGeneratedFiles;
+import org.springframework.aot.test.generate.compile.CompileWithTargetClassAccess;
+import org.springframework.aot.test.generate.compile.TestCompiler;
+import org.springframework.beans.factory.config.BeanDefinition;
+import org.springframework.beans.factory.support.GenericBeanDefinition;
+import org.springframework.boot.SpringBootConfiguration;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Import;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.test.context.BootstrapUtils;
+import org.springframework.test.context.MergedContextConfiguration;
+import org.springframework.test.context.TestContextBootstrapper;
+import org.springframework.test.context.aot.AotContextLoader;
+import org.springframework.test.context.aot.AotTestContextInitializers;
+import org.springframework.test.context.aot.TestContextAotGenerator;
+import org.springframework.test.util.ReflectionTestUtils;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.function.ThrowingConsumer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link SpringBootContextLoader} when used in AOT mode.
+ *
+ * @author Phillip Webb
+ */
+@CompileWithTargetClassAccess
+class SpringBootContextLoaderAotTests {
+
+	@Test
+	void loadContextForAotProcessingAndAotRuntime() {
+		InMemoryGeneratedFiles generatedFiles = new InMemoryGeneratedFiles();
+		TestContextAotGenerator generator = new TestContextAotGenerator(generatedFiles);
+		Class<?> testClass = ExampleTest.class;
+		generator.processAheadOfTime(Stream.of(testClass));
+		TestCompiler.forSystem().withFiles(generatedFiles).printFiles(System.out)
+				.compile(ThrowingConsumer.of((compiled) -> assertCompiledTest(testClass)));
+	}
+
+	private void assertCompiledTest(Class<?> testClass) throws Exception {
+		try {
+			System.setProperty(AotDetector.AOT_ENABLED, "true");
+			resetAotClasses();
+			AotTestContextInitializers aotContextInitializers = new AotTestContextInitializers();
+			TestContextBootstrapper testContextBootstrapper = BootstrapUtils.resolveTestContextBootstrapper(testClass);
+			MergedContextConfiguration mergedConfig = testContextBootstrapper.buildMergedContextConfiguration();
+			ApplicationContextInitializer<ConfigurableApplicationContext> contextInitializer = aotContextInitializers
+					.getContextInitializer(testClass);
+			ConfigurableApplicationContext context = (ConfigurableApplicationContext) ((AotContextLoader) mergedConfig
+					.getContextLoader()).loadContextForAotRuntime(mergedConfig, contextInitializer);
+			assertThat(context).isExactlyInstanceOf(GenericApplicationContext.class);
+			String[] beanNames = context.getBeanNamesForType(ExampleBean.class);
+			BeanDefinition beanDefinition = context.getBeanFactory().getBeanDefinition(beanNames[0]);
+			assertThat(beanDefinition).isNotExactlyInstanceOf(GenericBeanDefinition.class);
+		}
+		finally {
+			System.clearProperty(AotDetector.AOT_ENABLED);
+			resetAotClasses();
+		}
+	}
+
+	private void resetAotClasses() {
+		reset("org.springframework.test.context.aot.AotTestAttributesFactory");
+		reset("org.springframework.test.context.aot.AotTestContextInitializersFactory");
+	}
+
+	private void reset(String className) {
+		Class<?> targetClass = ClassUtils.resolveClassName(className, null);
+		ReflectionTestUtils.invokeMethod(targetClass, "reset");
+	}
+
+	@SpringBootTest(classes = ExampleConfig.class, webEnvironment = WebEnvironment.NONE)
+	static class ExampleTest {
+
+	}
+
+	@SpringBootConfiguration
+	@Import(ExampleBean.class)
+	static class ExampleConfig {
+
+	}
+
+	static class ExampleBean {
+
+	}
+
+}