Add module to support testing of generated code

Add a new unpublished `spring-core-test` module to support testing of
generated code. The module include a `TestCompiler` class which can be
used to dynamically compile generated Java code. It also include an
AssertJ friendly `SourceFile` class which uses qdox to provide targeted
assertions on specific parts of a generated source file.

See gh-28120

Author: philwebb

build.gradle

@@ -74,6 +74,7 @@ configure(allprojects) { project ->
 			dependency "com.google.code.gson:gson:2.8.9"
 			dependency "com.google.protobuf:protobuf-java-util:3.19.3"
 			dependency "com.googlecode.protobuf-java-format:protobuf-java-format:1.4"
+			dependency "com.thoughtworks.qdox:qdox:2.0.1"
 			dependency("com.thoughtworks.xstream:xstream:1.4.18") {
 				exclude group: "xpp3", name: "xpp3_min"
 				exclude group: "xmlpull", name: "xmlpull"

framework-bom/framework-bom.gradle

@@ -7,7 +7,7 @@ group = "org.springframework"
 
 dependencies {
 	constraints {
-		parent.moduleProjects.sort { "$it.name" }.each {
+		parent.moduleProjects.findAll{ it.name != 'spring-core-test' }.sort{ "$it.name" }.each {
 			api it
 		}
 	}

settings.gradle

@@ -18,6 +18,7 @@ include "spring-context"
 include "spring-context-indexer"
 include "spring-context-support"
 include "spring-core"
+include "spring-core-test"
 include "spring-expression"
 include "spring-instrument"
 include "spring-jcl"

spring-core-test/spring-core-test.gradle

@@ -0,0 +1,13 @@
+import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
+
+description = "Spring Core Test"
+
+dependencies {
+	api(project(":spring-core"))
+	api("org.assertj:assertj-core")
+	api("com.thoughtworks.qdox:qdox")
+}
+
+tasks.withType(PublishToMavenRepository).configureEach {
+	it.enabled = false
+}

spring-core-test/src/main/java/org/springframework/aot/test/generator/compile/CompilationException.java

@@ -0,0 +1,32 @@
+/*
+ * 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.aot.test.generator.compile;
+
+/**
+ * Exception thrown when code cannot compile.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ */
+@SuppressWarnings("serial")
+public class CompilationException extends RuntimeException {
+
+	CompilationException(String message) {
+		super(message);
+	}
+
+}

spring-core-test/src/main/java/org/springframework/aot/test/generator/compile/Compiled.java

@@ -0,0 +1,169 @@
+/*
+ * 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.aot.test.generator.compile;
+
+import java.lang.reflect.Constructor;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.springframework.aot.test.generator.file.ResourceFile;
+import org.springframework.aot.test.generator.file.ResourceFiles;
+import org.springframework.aot.test.generator.file.SourceFile;
+import org.springframework.aot.test.generator.file.SourceFiles;
+import org.springframework.util.Assert;
+
+/**
+ * Fully compiled results provided from a {@link TestCompiler}.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ */
+public class Compiled {
+
+
+	private final ClassLoader classLoader;
+
+	private final SourceFiles sourceFiles;
+
+	private final ResourceFiles resourceFiles;
+
+	private List<Class<?>> compiledClasses;
+
+
+	Compiled(ClassLoader classLoader, SourceFiles sourceFiles,
+			ResourceFiles resourceFiles) {
+		this.classLoader = classLoader;
+		this.sourceFiles = sourceFiles;
+		this.resourceFiles = resourceFiles;
+	}
+
+
+	/**
+	 * Return the classloader containing the compiled content and access to the
+	 * resources.
+	 * @return the classLoader
+	 */
+	public ClassLoader getClassLoader() {
+		return this.classLoader;
+	}
+
+	/**
+	 * Return the single source file that was compiled.
+	 * @return the single source file
+	 * @throws IllegalStateException if the compiler wasn't passed exactly one
+	 * file
+	 */
+	public SourceFile getSourceFile() {
+		return this.sourceFiles.getSingle();
+	}
+
+	/**
+	 * Return all source files that were compiled.
+	 * @return the source files used by the compiler
+	 */
+	public SourceFiles getSourceFiles() {
+		return this.sourceFiles;
+	}
+
+	/**
+	 * Return the single resource file that was used when compiled.
+	 * @return the single resource file
+	 * @throws IllegalStateException if the compiler wasn't passed exactly one
+	 * file
+	 */
+	public ResourceFile getResourceFile() {
+		return this.resourceFiles.getSingle();
+	}
+
+	/**
+	 * Return all resource files that were compiled.
+	 * @return the resource files used by the compiler
+	 */
+	public ResourceFiles getResourceFiles() {
+		return this.resourceFiles;
+	}
+
+	/**
+	 * Return a new instance of a compiled class of the given type. There must
+	 * be only a single instance and it must have a default constructor.
+	 * @param <T> the required type
+	 * @param type the required type
+	 * @return an instance of type created from the compiled classes
+	 * @throws IllegalStateException if no instance can be found or instantiated
+	 */
+	public <T> T getInstance(Class<T> type) {
+		List<Class<?>> matching = getAllCompiledClasses().stream().filter(
+				candidate -> type.isAssignableFrom(candidate)).toList();
+		Assert.state(!matching.isEmpty(), () -> "No instance found of type " + type.getName());
+		Assert.state(matching.size() == 1, () -> "Multiple instances found of type " + type.getName());
+		return newInstance(matching.get(0));
+	}
+
+	/**
+	 * Return an instance of a compiled class identified by its class name. The
+	 * class must have a default constructor.
+	 * @param <T> the type to return
+	 * @param type the type to return
+	 * @param className the class name to load
+	 * @return an instance of the class
+	 * @throws IllegalStateException if no instance can be found or instantiated
+	 */
+	public <T> T getInstance(Class<T> type, String className) {
+		Class<?> loaded = loadClass(className);
+		return newInstance(loaded);
+	}
+
+	/**
+	 * Return all compiled classes.
+	 * @return a list of all compiled classes
+	 */
+	public List<Class<?>> getAllCompiledClasses() {
+		List<Class<?>> compiledClasses = this.compiledClasses;
+		if (compiledClasses == null) {
+			compiledClasses = new ArrayList<>();
+			this.sourceFiles.stream().map(this::loadClass).forEach(compiledClasses::add);
+			this.compiledClasses = Collections.unmodifiableList(compiledClasses);
+		}
+		return compiledClasses;
+	}
+
+	@SuppressWarnings("unchecked")
+	private <T> T newInstance(Class<?> loaded) {
+		try {
+			Constructor<?> constructor = loaded.getDeclaredConstructor();
+			return (T) constructor.newInstance();
+		}
+		catch (Exception ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
+	private Class<?> loadClass(SourceFile sourceFile) {
+		return loadClass(sourceFile.getClassName());
+	}
+
+	private Class<?> loadClass(String className) {
+		try {
+			return this.classLoader.loadClass(className);
+		}
+		catch (ClassNotFoundException ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
+}

spring-core-test/src/main/java/org/springframework/aot/test/generator/compile/DynamicClassFileObject.java

@@ -0,0 +1,63 @@
+/*
+ * 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.aot.test.generator.compile;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.URI;
+
+import javax.tools.JavaFileObject;
+import javax.tools.SimpleJavaFileObject;
+
+/**
+ * In-memory {@link JavaFileObject} used to hold class bytecode.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ */
+class DynamicClassFileObject extends SimpleJavaFileObject {
+
+	private volatile byte[] bytes;
+
+
+	DynamicClassFileObject(String className) {
+		super(URI.create("class:///" + className.replace('.', '/') + ".class"),
+				Kind.CLASS);
+	}
+
+
+	@Override
+	public OutputStream openOutputStream() throws IOException {
+		return new JavaClassOutputStream();
+	}
+
+	byte[] getBytes() {
+		return this.bytes;
+	}
+
+
+	class JavaClassOutputStream extends ByteArrayOutputStream {
+
+		@Override
+		public void close() throws IOException {
+			DynamicClassFileObject.this.bytes = toByteArray();
+		}
+
+	}
+
+}