Support javac as a compiler for Tycho

Currently Tycho is strictly using ecj as a compiler but in general it
might be there are situations one wants to use javac for compilation
even though it might not has full features supported (e.g. package
restrictions).

This is an attempt to make it possible to use javac at a very basic
level.

tycho-compiler-plugin/pom.xml

@@ -87,6 +87,11 @@
 			<artifactId>bcel</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+		    <groupId>org.codehaus.plexus</groupId>
+		    <artifactId>plexus-compiler-javac</artifactId>
+		    <version>2.14.2</version>
+		</dependency>
 	</dependencies>
 
 	<build>

tycho-its/projects/tycho-compiler-plugin/javac/pom.xml

@@ -0,0 +1,36 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+
+	<groupId>org.eclipse.tycho.it</groupId>
+	<artifactId>javac.parent</artifactId>
+	<version>1.0.0-SNAPSHOT</version>
+	<packaging>pom</packaging>
+	<properties>
+		<tycho-version>5.0.0-SNAPSHOT</tycho-version>
+	</properties>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.eclipse.tycho</groupId>
+				<artifactId>tycho-maven-plugin</artifactId>
+				<version>${tycho-version}</version>
+				<extensions>true</extensions>
+			</plugin>
+			<plugin>
+				<groupId>org.eclipse.tycho</groupId>
+				<artifactId>tycho-compiler-plugin</artifactId>
+				<version>${tycho-version}</version>
+				<configuration>
+					<compilerId>javac</compilerId>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+
+	<modules>
+		<module>simple</module>
+	</modules>
+</project>

tycho-its/projects/tycho-compiler-plugin/javac/simple/META-INF/MANIFEST.MF

@@ -0,0 +1,4 @@
+Manifest-Version: 1.0
+Bundle-ManifestVersion: 2
+Bundle-SymbolicName: simple
+Bundle-Version: 1.0.0.qualifier

tycho-its/projects/tycho-compiler-plugin/javac/simple/build.properties

@@ -0,0 +1,4 @@
+source.. = src/
+output.. = bin/
+bin.includes = META-INF/,\
+               .

tycho-its/projects/tycho-compiler-plugin/javac/simple/pom.xml

@@ -0,0 +1,13 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>org.eclipse.tycho.it</groupId>
+		<artifactId>javac.parent</artifactId>
+		<version>1.0.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>simple</artifactId>
+
+	<packaging>eclipse-plugin</packaging>
+
+</project>

tycho-its/projects/tycho-compiler-plugin/javac/simple/src/Test.java

@@ -0,0 +1,19 @@
+/*******************************************************************************
+ * Copyright (c) 2012 SAP AG and others.
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     SAP AG - initial API and implementation
+ *******************************************************************************/
+
+public class Test
+{
+    public static void main(String[] args) {
+        int a = 0;
+    }
+}

tycho-its/src/test/java/org/eclipse/tycho/test/CompilerPluginTest.java

@@ -0,0 +1,30 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Christoph Läubrich and others.
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Christoph Läubrich - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.tycho.test;
+
+import org.apache.maven.it.Verifier;
+import org.junit.Test;
+
+/**
+ * Test for the tycho-compiler-plugin
+ */
+public class CompilerPluginTest extends AbstractTychoIntegrationTest {
+
+	@Test
+	public void testJavac() throws Exception {
+		Verifier verifier = getVerifier("tycho-compiler-plugin/javac", true, true);
+		verifier.executeGoal("compile");
+		verifier.verifyErrorFreeLog();
+	}
+
+}