Support javac as a compiler for Tycho

RELEASE_NOTES.md

@@ -6,6 +6,22 @@ If you are reading this in the browser, then you can quickly jump to specific ve
 
 ## 5.0.0 (under development)
 
+### using javac as the compiler for Tycho
+
+You can now use `javac` as the compiler backend for Tycho by adding the following configuration:
+
+```xml
+<plugin>
+	<groupId>org.eclipse.tycho</groupId>
+	<artifactId>tycho-compiler-plugin</artifactId>
+	<version>${tycho.version}</version>
+	<configuration>
+		<compilerId>javac</compilerId>
+	</configuration>
+</plugin>
+ ```
+
+
 ### new `mirror-target-platform`
 
 There is a new `mirror-target-platform` that allows to mirror the current target platform of a project into a P2 update site, this can b enabled for a project like this:

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-compiler-plugin/src/main/java/copied/org/apache/maven/plugin/AbstractCompilerMojo.java

@@ -57,6 +57,8 @@
  */
 public abstract class AbstractCompilerMojo extends AbstractMojo {
 
+    protected static final String JDT_COMPILER_ID = "jdt";
+
     public static final String DEFAULT_SOURCE_VERSION = "11";
 
     public static final String DEFAULT_TARGET_VERSION = "11";
@@ -144,8 +146,8 @@ public abstract class AbstractCompilerMojo extends AbstractMojo {
     /**
      * The compiler id of the compiler to use.
      */
-    @Parameter(property = "maven.compiler.compilerId", defaultValue = "jdt")
-    private String compilerId;
+    @Parameter(property = "maven.compiler.compilerId", defaultValue = JDT_COMPILER_ID)
+    protected String compilerId;
 
     /**
      * Version of the compiler to use, ex. "1.3", "1.5", if fork is set to true

tycho-compiler-plugin/src/main/java/org/eclipse/tycho/compiler/AbstractOsgiCompilerMojo.java

@@ -573,6 +573,7 @@ public List<String> getClasspathElements() throws MojoExecutionException {
         final List<String> classpath = new ArrayList<>();
         Set<String> seen = new HashSet<>();
         Set<String> includedPathes = new HashSet<>();
+        boolean useAccessRules = JDT_COMPILER_ID.equals(compilerId);
         for (ClasspathEntry cpe : getClasspath()) {
             Stream<File> classpathLocations = Stream
                     .concat(cpe.getLocations().stream(),
@@ -581,7 +582,7 @@ public List<String> getClasspathElements() throws MojoExecutionException {
                     .filter(AbstractOsgiCompilerMojo::isValidLocation).distinct();
             classpathLocations.forEach(location -> {
                 String path = location.getAbsolutePath();
-                String entry = path + toString(cpe.getAccessRules());
+                String entry = path + toString(cpe.getAccessRules(), useAccessRules);
                 if (seen.add(entry)) {
                     includedPathes.add(path);
                     classpath.add(entry);
@@ -646,19 +647,22 @@ protected BundleProject getBundleProject() throws MojoExecutionException {
         return (BundleProject) projectType;
     }
 
-    private String toString(Collection<AccessRule> rules) {
-        StringJoiner result = new StringJoiner(RULE_SEPARATOR, "[", "]"); // include all
-        if (rules != null) {
-            for (AccessRule rule : rules) {
-                result.add((rule.isDiscouraged() ? "~" : "+") + rule.getPattern());
+    private String toString(Collection<AccessRule> rules, boolean useAccessRules) {
+        if (useAccessRules) {
+            StringJoiner result = new StringJoiner(RULE_SEPARATOR, "[", "]"); // include all
+            if (rules != null) {
+                for (AccessRule rule : rules) {
+                    result.add((rule.isDiscouraged() ? "~" : "+") + rule.getPattern());
+                }
+                result.add(RULE_EXCLUDE_ALL);
+            } else {
+                // include everything, not strictly necessary, but lets make this obvious
+                //result.append("[+**/*]");
+                return "";
             }
-            result.add(RULE_EXCLUDE_ALL);
-        } else {
-            // include everything, not strictly necessary, but lets make this obvious
-            //result.append("[+**/*]");
-            return "";
+            return result.toString();
         }
-        return result.toString();
+        return "";
     }
 
     @Override
@@ -719,7 +723,7 @@ protected CompilerConfiguration getCompilerConfiguration(List<String> compileSou
                 List<Entry<String, String>> copy = new ArrayList<>(
                         compilerConfiguration.getCustomCompilerArgumentsEntries());
                 compilerConfiguration.getCustomCompilerArgumentsEntries().clear();
-                compilerConfiguration.addCompilerCustomArgument("-properties", prefsFilePath);
+                addCompilerCustomArgument(compilerConfiguration, "-properties", prefsFilePath);
                 compilerConfiguration.getCustomCompilerArgumentsEntries().addAll(copy);
             }
         }
@@ -738,7 +742,7 @@ protected CompilerConfiguration getCompilerConfiguration(List<String> compileSou
                 if (jreClasspathEntry.isModule()) {
                     Collection<String> modules = jreClasspathEntry.getLimitModules();
                     if (!modules.isEmpty()) {
-                        compilerConfiguration.addCompilerCustomArgument("--limit-modules", String.join(",", modules));
+                        addCompilerCustomArgument(compilerConfiguration, "--limit-modules", String.join(",", modules));
                     }
                 }
             }
@@ -782,7 +786,7 @@ private void configureCompilerLog(CompilerConfiguration compilerConfiguration) t
             fileExtension = "log";
         }
         logPath = logPath + logFileName + "." + fileExtension;
-        compilerConfiguration.addCompilerCustomArgument("-log", logPath);
+        addCompilerCustomArgument(compilerConfiguration, "-log", logPath);
     }
 
     private void configureBootclasspathAccessRules(CompilerConfiguration compilerConfiguration)
@@ -811,8 +815,8 @@ private void configureBootclasspathAccessRules(CompilerConfiguration compilerCon
                     .addAll(getBundleProject().getBootClasspathExtraAccessRules(DefaultReactorProject.adapt(project)));
         }
         if (!accessRules.isEmpty()) {
-            compilerConfiguration.addCompilerCustomArgument("org.osgi.framework.system.packages",
-                    toString(accessRules));
+            addCompilerCustomArgument(compilerConfiguration, "org.osgi.framework.system.packages",
+                    toString(accessRules, true));
         }
     }
 
@@ -837,7 +841,7 @@ private void configureJavaHome(CompilerConfiguration compilerConfiguration) thro
                     .orElseThrow(() -> new MojoExecutionException(
                             "useJDK = BREE configured, but no toolchain of type 'jdk' with id '" + toolchainId
                                     + "' found. See https://maven.apache.org/guides/mini/guide-using-toolchains.html"));
-            compilerConfiguration.addCompilerCustomArgument("use.java.home", osgiToolchain.getJavaHome());
+            addCompilerCustomArgument(compilerConfiguration, "use.java.home", osgiToolchain.getJavaHome());
             configureBootClassPath(compilerConfiguration, osgiToolchain);
         }
     }
@@ -851,14 +855,22 @@ private void configureBootClassPath(CompilerConfiguration compilerConfiguration,
                 if (includeParent != null) {
                     Xpp3Dom[] includes = includeParent.getChildren("include");
                     if (includes.length > 0) {
-                        compilerConfiguration.addCompilerCustomArgument("-bootclasspath", scanBootclasspath(
+                        addCompilerCustomArgument(compilerConfiguration, "-bootclasspath", scanBootclasspath(
                                 osgiToolchain.getJavaHome(), includes, bootClassPath.getChild("excludes")));
                     }
                 }
             }
         }
     }
 
+    protected boolean addCompilerCustomArgument(CompilerConfiguration compilerConfiguration, String key, String value) {
+        if (JDT_COMPILER_ID.equals(compilerId)) {
+            compilerConfiguration.addCompilerCustomArgument(key, value);
+            return true;
+        }
+        return false;
+    }
+
     private String scanBootclasspath(String javaHome, Xpp3Dom[] includes, Xpp3Dom excludeParent) {
         DirectoryScanner scanner = new DirectoryScanner();
         scanner.setBasedir(javaHome);

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();
+	}
+
+}