[fixes #3143] Maven+ECJ Agent Bootstrap

* Adds AgentBootstrap, the actual bootstrapping agent
* Adds MavenEcjBootstrapApp, the command line app for generating the
appropriate files
* Updates the build to package these correctly
* Updates the documentation for setup/ecj

buildScripts/compile.ant.xml

@@ -74,7 +74,21 @@ This buildfile is part of projectlombok.org. It takes care of compiling and buil
 		</jar>
 	</target>
 
-	<target name="compile" depends="version, deps, -setup.build, create.spiProcessor" description="Compiles the code">
+	<target name="create.agentBootstrap" depends="-setup.build" description="Compiles the Maven ECJ bootstrap agent">
+		<ivy:compile destdir="build/agentBootstrap" source="1.6" target="1.6" ecj="true">
+			<bootclasspath path="${jdk6-rt.loc}" />
+			<src path="src/eclipseAgent" />
+			<include name="lombok/launch/AgentBootstrap.java" />
+		</ivy:compile>
+		<jar destfile="build/lombok-main/lombok/eclipse/agent/lombok-bootstrap.jar" basedir="build/agentBootstrap" includes="lombok/launch/AgentBootstrap*.class">
+			<manifest>
+				<attribute name="Premain-Class" value="lombok.launch.AgentBootstrap" />
+				<attribute name="Can-Redefine-Classes" value="true" />
+			</manifest>
+		</jar>
+	</target>
+
+	<target name="compile" depends="version, deps, -setup.build, create.spiProcessor, create.agentBootstrap" description="Compiles the code">
 		<!--
 			1. Compile stubs.
 			2. Compile transplants.
@@ -169,6 +183,7 @@ This buildfile is part of projectlombok.org. It takes care of compiling and buil
 			<src path="src/eclipseAgent" />
 			<src path="src/delombok" />
 			<exclude name="**/*Transplants.java" />
+			<exclude name="**/AgentBootstrap.java" />
 			<classpath refid="cp.build" />
 			<classpath refid="cp.eclipse-oxygen" />
 			<classpath refid="cp.javac6" />

src/eclipseAgent/lombok/eclipse/agent/MavenEcjBootstrapApp.java

@@ -0,0 +1,170 @@
+/*
+ * Copyright (C) 2009-2022 The Project Lombok Authors.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package lombok.eclipse.agent;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.FileWriter;
+import java.io.InputStream;
+import java.io.PrintStream;
+import java.util.Arrays;
+import java.util.List;
+
+import com.zwitserloot.cmdreader.CmdReader;
+import com.zwitserloot.cmdreader.Description;
+import com.zwitserloot.cmdreader.InvalidCommandLineException;
+import com.zwitserloot.cmdreader.Shorthand;
+
+import lombok.core.LombokApp;
+import lombok.spi.Provides;
+
+@Provides
+public class MavenEcjBootstrapApp extends LombokApp {
+	@Override public String getAppName() {
+		return "createMavenECJBootstrap";
+	}
+
+	@Override public String getAppDescription() {
+		return "Creates .mvn/jvm.config and .mvn/lombok-bootstrap.jar for\n" +
+				"use with the ECJ compiler.";
+	}
+
+	@Override public List<String> getAppAliases() {
+		return Arrays.asList("ecj");
+	}
+
+	private static class CmdArgs {
+		@Shorthand("w")
+		@Description("Overwrite existing files. Defaults to false.")
+		boolean overwrite = false;
+
+		@Shorthand("o")
+		@Description("The root of a Maven project. Defaults to the current working directory.")
+		String output;
+
+		@Shorthand({"h", "?"})
+		@Description("Shows this help text")
+		boolean help;
+	}
+
+	@Override public int runApp(List<String> rawArgs) throws Exception {
+		CmdReader<CmdArgs> reader = CmdReader.of(CmdArgs.class);
+		CmdArgs args;
+		try {
+			args = reader.make(rawArgs.toArray(new String[0]));
+		} catch (InvalidCommandLineException e) {
+			printHelp(reader, e.getMessage(), System.err);
+			return 1;
+		}
+
+		if (args.help) {
+			printHelp(reader, null, System.out);
+			return 0;
+		}
+
+		return createBootstrap(args.output, args.overwrite);
+	}
+
+	private int createBootstrap(String root, boolean overwrite) {
+		File mvn = new File(root, ".mvn");
+		int result = 0;
+		if (result == 0) result = makeMvn(mvn);
+		if (result == 0) result = makeJvmConfig(mvn, overwrite);
+		if (result == 0) result = makeJar(mvn, overwrite);
+		return result;
+	}
+
+	private int makeMvn(File mvn) {
+		int result = 0;
+		Exception err = null;
+		try {
+			if (!mvn.exists() && !mvn.mkdirs()) result = 1;
+		} catch (Exception e) {
+			result = 1;
+			err = e;
+		}
+		if (result != 0) {
+			System.err.println("Could not create "+mvn.getPath());
+			if (err != null) err.printStackTrace(System.err);
+		}
+		return result;
+	}
+
+	private int makeJvmConfig(File mvn, boolean overwrite) {
+		File jvmConfig = new File(mvn, "jvm.config");
+		if (jvmConfig.exists() && !overwrite) {
+			System.err.println(canonical(jvmConfig) + " exists but '-w' not specified.");
+			return 1;
+		}
+		try {
+			FileWriter writer = new FileWriter(jvmConfig);
+			writer.write("-javaagent:.mvn/lombok-bootstrap.jar");
+			writer.flush();
+			writer.close();
+			System.out.println("Successfully created: " + canonical(jvmConfig));
+			return 0;
+		} catch (Exception e) {
+			System.err.println("Could not create: " + canonical(jvmConfig));
+			e.printStackTrace(System.err);
+			return 1;
+		}
+	}
+
+	private int makeJar(File mvn, boolean overwrite) {
+		File jar = new File(mvn, "lombok-bootstrap.jar");
+		if (jar.exists() && !overwrite) {
+			System.err.println(canonical(jar) + " but '-w' not specified.");
+			return 1;
+		}
+		try {
+			InputStream input = this.getClass().getResourceAsStream("/lombok/eclipse/agent/lombok-bootstrap.jar");
+			FileOutputStream output = new FileOutputStream(jar);
+			byte[] buffer = new byte[4096];
+			int length;
+			while ((length = input.read(buffer)) > 0) output.write(buffer, 0, length);
+			output.flush();
+			output.close();
+			System.out.println("Successfully created: " + canonical(jar));
+			return 0;
+		} catch (Exception e) {
+			System.err.println("Could not create: " + canonical(jar));
+			e.printStackTrace(System.err);
+			return 1;
+		}
+	}
+
+	private static String canonical(File out) {
+		try {
+			return out.getCanonicalPath();
+		} catch (Exception e) {
+			return out.getAbsolutePath();
+		}
+	}
+
+	private void printHelp(CmdReader<CmdArgs> reader, String message, PrintStream out) {
+		if (message != null) {
+			out.println(message);
+			out.println("----------------------------");
+		}
+		out.println(reader.generateCommandLineHelp("java -jar lombok.jar createMavenECJBootstrap"));
+	}
+}

src/eclipseAgent/lombok/launch/AgentBootstrap.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 2009-2022 The Project Lombok Authors.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package lombok.launch;
+
+import java.lang.instrument.ClassFileTransformer;
+import java.lang.instrument.IllegalClassFormatException;
+import java.lang.instrument.Instrumentation;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.security.ProtectionDomain;
+import java.util.jar.JarFile;
+
+/**
+ * This Java agent does not transform bytecode, but acts as a watcher that can figure out when it is appropriate to load
+ * Lombok itself within a Maven execution. It relies on several facts:
+ * <ul>
+ * <li>maven-compiler-plugin contains an AbstractCompilerMojo class that compiler instances extend.
+ * <li>Maven loaders are ClassRealms, which extend URLClassLoader.
+ * <li>Each plugin dependency in the pom.xml is represented as a file URL on the ClassRealm that points to the artifact.
+ * <li>URLs to Maven artifacts contain the group and artifact ids ([...]/groupid/artifactid/ver/artifactid-ver.jar).
+ * <li>The Lombok Java agent class is lombok.launch.Agent.
+ * </ul>
+ * Given all of the above, the transformer simply waits for AbstractCompilerMojo to be loaded, then uses the loader to
+ * find the path to the Lombok jar file, and finally loads the Lombok agent using reflection.
+ */
+public final class AgentBootstrap
+{
+    private static final String MAVEN_COMPILER_TRIGGER_CLASS = "org/apache/maven/plugin/compiler/AbstractCompilerMojo";
+    private static final String LOMBOK_URL_IDENTIFIER = "/org/projectlombok/lombok/";
+    private static final String LOMBOK_AGENT_CLASS = "lombok.launch.Agent";
+    private static final byte[] NOT_TRANSFORMED = null;
+
+    private AgentBootstrap()
+    {}
+
+    /**
+     * Invoked when agent is added via -javaagent argument.
+     *
+     * @param agentArgs
+     *            arguments
+     * @param instrumentation
+     *            service provider
+     */
+    public static void premain(final String agentArgs, final Instrumentation instrumentation)
+    {
+        instrumentation.addTransformer(new ClassFileTransformer() {
+            @Override
+            public byte[] transform(final ClassLoader loader, final String className, final Class<?> cbr, final ProtectionDomain pd,
+                    final byte[] cfb)
+                throws IllegalClassFormatException
+            {
+                if (MAVEN_COMPILER_TRIGGER_CLASS.equals(className)) {
+                    for (final URL url : ((URLClassLoader)loader).getURLs()) {
+                        if (url.getPath().contains(LOMBOK_URL_IDENTIFIER)) {
+                            try {
+                                instrumentation.appendToSystemClassLoaderSearch(new JarFile(url.getPath()));
+                                AgentBootstrap.class.getClassLoader().loadClass(LOMBOK_AGENT_CLASS)
+                                        .getDeclaredMethod("premain", String.class, Instrumentation.class)
+                                        .invoke(null, agentArgs, instrumentation);
+                                instrumentation.removeTransformer(this);
+                                break;
+                            } catch (final Exception e) {
+                                //There are no appropriate loggers available at this point in time.
+                                e.printStackTrace(System.err);
+                            }
+                        }
+                    }
+                }
+                return NOT_TRANSFORMED;
+            }
+        });
+    }
+}