Add entry point for processing an application ahead-of-time

This commit adds the necessary infrastructure to process an application
using the AOT engine, similar to the existing TestAotProcessor for
processing tests.

This can be used by frameworks built on top of Spring Framework, for
instance by providing a main method that can be triggered by build
tools.

Close gh-29181

spring-context/src/test/java/org/springframework/context/aot/AotProcessorTests.java

@@ -0,0 +1,148 @@
+/*
+ * 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.context.aot;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Collections;
+import java.util.List;
+import java.util.function.Consumer;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.javapoet.ClassName;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link AotProcessor}.
+ *
+ * @author Stephane Nicoll
+ */
+class AotProcessorTests {
+
+	@Test
+	void processGeneratesAssets(@TempDir Path directory) {
+		GenericApplicationContext context = new AnnotationConfigApplicationContext();
+		context.registerBean(SampleApplication.class);
+		AotProcessor processor = new TestAotProcessor(SampleApplication.class, directory);
+		ClassName className = processor.process();
+		assertThat(className).isEqualTo(ClassName.get(SampleApplication.class.getPackageName(),
+				"AotProcessorTests_SampleApplication__ApplicationContextInitializer"));
+		assertThat(directory).satisfies(hasGeneratedAssetsForSampleApplication());
+	}
+
+	@Test
+	void processingDeletesExistingOutput(@TempDir Path directory) throws IOException {
+		Path sourceOutput = directory.resolve("source");
+		Path resourceOutput = directory.resolve("resource");
+		Path classOutput = directory.resolve("class");
+		Path existingSourceOutput = createExisting(sourceOutput);
+		Path existingResourceOutput = createExisting(resourceOutput);
+		Path existingClassOutput = createExisting(classOutput);
+		AotProcessor processor = new TestAotProcessor(SampleApplication.class,
+				sourceOutput, resourceOutput, classOutput);
+		processor.process();
+		assertThat(existingSourceOutput).doesNotExist();
+		assertThat(existingResourceOutput).doesNotExist();
+		assertThat(existingClassOutput).doesNotExist();
+	}
+
+	@Test
+	void processWithEmptyNativeImageArgumentsDoesNotCreateNativeImageProperties(@TempDir Path directory) {
+		GenericApplicationContext context = new AnnotationConfigApplicationContext();
+		context.registerBean(SampleApplication.class);
+		AotProcessor processor = new TestAotProcessor(SampleApplication.class, directory) {
+			@Override
+			protected List<String> getDefaultNativeImageArguments(String application) {
+				return Collections.emptyList();
+			}
+		};
+		processor.process();
+		assertThat(directory.resolve("resource/META-INF/native-image/com.example/example/native-image.properties"))
+				.doesNotExist();
+	}
+
+	private Path createExisting(Path directory) throws IOException {
+		Path existing = directory.resolve("existing");
+		Files.createDirectories(directory);
+		Files.createFile(existing);
+		return existing;
+	}
+
+	private Consumer<Path> hasGeneratedAssetsForSampleApplication() {
+		return directory -> {
+			assertThat(directory.resolve(
+					"source/org/springframework/context/aot/AotProcessorTests_SampleApplication__ApplicationContextInitializer.java"))
+					.exists().isRegularFile();
+			assertThat(directory.resolve("source/org/springframework/context/aot/AotProcessorTests__BeanDefinitions.java"))
+					.exists().isRegularFile();
+			assertThat(directory.resolve(
+					"source/org/springframework/context/aot/AotProcessorTests_SampleApplication__BeanFactoryRegistrations.java"))
+					.exists().isRegularFile();
+			assertThat(directory.resolve("resource/META-INF/native-image/com.example/example/reflect-config.json"))
+					.exists().isRegularFile();
+			Path nativeImagePropertiesFile = directory
+					.resolve("resource/META-INF/native-image/com.example/example/native-image.properties");
+			assertThat(nativeImagePropertiesFile).exists().isRegularFile().hasContent("""
+					Args = -H:Class=org.springframework.context.aot.AotProcessorTests$SampleApplication \\
+					--report-unsupported-elements-at-runtime \\
+					--no-fallback \\
+					--install-exit-handlers
+					""");
+		};
+	}
+
+
+	private static class TestAotProcessor extends AotProcessor {
+
+		public TestAotProcessor(Class<?> application,
+				Path sourceOutput, Path resourceOutput, Path classOutput) {
+			super(application, sourceOutput, resourceOutput, classOutput, "com.example", "example");
+		}
+
+		public TestAotProcessor(Class<?> application, Path rootPath) {
+			super(application, rootPath.resolve("source"), rootPath.resolve("resource"),
+					rootPath.resolve("class"), "com.example", "example");
+		}
+
+		@Override
+		protected GenericApplicationContext prepareApplicationContext(Class<?> application) {
+			AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+			context.register(application);
+			return context;
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class SampleApplication {
+
+		@Bean
+		public String testBean() {
+			return "Hello";
+		}
+
+	}
+
+}