Initial support of multi-releases project by using the <source> element.

Initial support of modular project (JPMS) by using the `<module>` element.
Currently support only one or the other, not yet both in same time.

Contains fixes for incremental build:
* The `package-info.java` source files may produce no output.
* Provide an option to rebuild everything as soon as one file changed.

The `additions` aspect has been renamed `rebuild-on-add` for clarity and
for consistency with `rebuild-on-change` added in the last above point.

Author: desruisseaux

src/it/MCOMPILER-192/verify.groovy

@@ -22,7 +22,7 @@ assert logFile.exists()
 def content = logFile.getText('UTF-8')
 
 def causedByExpected = content.contains ( 'Caused by: org.apache.maven.plugin.compiler.CompilationFailureException:' )
-def twoFilesBeingCompiled = content.contains ( 'Compiling 2 source files' )
+def twoFilesBeingCompiled = content.contains ( 'Compiling all files' )
 def checkResult = content.contains ( 'BUILD FAILURE' )
 def compilationFailure1 = content.contains( '[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:')
 def compilationFailure2 = content.contains( ':compile (default-compile) on project blah: Cannot compile')

src/it/mcompiler-21_methodname-change/pom.xml

@@ -35,6 +35,9 @@ under the License.
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-compiler-plugin</artifactId>
           <version>@project.version@</version>
+          <configuration>
+            <incrementalCompilation>sources,rebuild-on-change</incrementalCompilation>
+          </configuration>
         </plugin>
       </plugins>
     </pluginManagement>

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

@@ -18,6 +18,8 @@
  */
 package org.apache.maven.plugin.compiler;
 
+import javax.tools.DiagnosticListener;
+import javax.tools.JavaFileObject;
 import javax.tools.OptionChecker;
 
 import java.io.IOException;
@@ -237,6 +239,21 @@ protected String getDebugFileName() {
         return debugFileName;
     }
 
+    /**
+     * Creates a new task for compiling the main classes.
+     *
+     * @param listener where to send compilation warnings, or {@code null} for the Maven logger
+     * @throws MojoException if this method identifies an invalid parameter in this <abbr>MOJO</abbr>
+     * @return the task to execute for compiling the main code using the configuration in this <abbr>MOJO</abbr>
+     * @throws IOException if an error occurred while creating the output directory or scanning the source directories
+     */
+    @Override
+    public ToolExecutor createExecutor(DiagnosticListener<? super JavaFileObject> listener) throws IOException {
+        ToolExecutor executor = super.createExecutor(listener);
+        addImplicitDependencies(executor.sourceDirectories, executor.dependencies);
+        return executor;
+    }
+
     /**
      * If compiling a multi-release JAR in the old deprecated way, add the previous versions to the path.
      *
@@ -247,10 +264,8 @@ protected String getDebugFileName() {
      *
      * @deprecated For compatibility with the previous way to build multi-releases JAR file.
      */
-    @Override
     @Deprecated(since = "4.0.0")
-    final void addImplicitDependencies(
-            List<SourceDirectory> sourceDirectories, Map<PathType, List<Path>> addTo, boolean hasModuleDeclaration)
+    private void addImplicitDependencies(List<SourceDirectory> sourceDirectories, Map<PathType, List<Path>> addTo)
             throws IOException {
         if (SUPPORT_LEGACY && multiReleaseOutput) {
             var paths = new TreeMap<Integer, Path>();

src/main/java/org/apache/maven/plugin/compiler/CompilerMojo.java

@@ -89,8 +89,11 @@ final class DiagnosticLogger implements DiagnosticListener<JavaFileObject> {
      */
     @Override
     public void report(Diagnostic<? extends JavaFileObject> diagnostic) {
-        MessageBuilder record = messageBuilderFactory.builder();
         String message = diagnostic.getMessage(locale);
+        if (message == null || message.isBlank()) {
+            return;
+        }
+        MessageBuilder record = messageBuilderFactory.builder();
         record.a(message);
         Diagnostic.Kind kind = diagnostic.getKind();
         String style;
@@ -176,7 +179,7 @@ void logSummary() {
             patternForCount = patternForCount(Math.max(numWarnings, numErrors));
         }
         if ((numWarnings | numErrors) != 0) {
-            message.strong("Total:").newline();
+            message.strong("Total:");
         }
         if (numWarnings != 0) {
             writeCount(message, patternForCount, numWarnings, "warning");
@@ -200,10 +203,10 @@ private static String patternForCount(int n) {
      * Appends the count of warnings or errors, making them plural if needed.
      */
     private static void writeCount(MessageBuilder message, String patternForCount, int count, String name) {
+        message.newline();
         message.format(patternForCount, count, name);
         if (count > 1) {
             message.append('s');
         }
-        message.newline();
     }
 }

src/main/java/org/apache/maven/plugin/compiler/DiagnosticLogger.java

@@ -63,7 +63,7 @@ final class ForkedToolSources implements StandardJavaFileManager {
      * Option for source files. These options are not declared in
      * {@link JavaPathType} because they are not about dependencies.
      */
-    private enum SourcePathType implements PathType {
+    private enum OtherPathType implements PathType {
         /**
          * The option for the directory of source files.
          */
@@ -84,7 +84,7 @@ private enum SourcePathType implements PathType {
          */
         private final String option;
 
-        SourcePathType(String option) {
+        OtherPathType(String option) {
             this.option = option;
         }
 
@@ -411,11 +411,11 @@ public void setLocationFromPaths(Location location, Collection<? extends Path> p
         PathType type = JavaPathType.valueOf(location).orElse(null);
         if (type == null) {
             if (location == StandardLocation.SOURCE_OUTPUT) {
-                type = SourcePathType.GENERATED_SOURCES;
+                type = OtherPathType.GENERATED_SOURCES;
             } else if (location == StandardLocation.SOURCE_PATH) {
-                type = SourcePathType.SOURCES;
+                type = OtherPathType.SOURCES;
             } else if (location == StandardLocation.CLASS_OUTPUT) {
-                type = SourcePathType.OUTPUT;
+                type = OtherPathType.OUTPUT;
             } else {
                 throw new IllegalArgumentException("Unsupported location: " + location);
             }