refresh javac output to make sure Java project system recognize the o…

…utput changes

org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacCompiler.java

@@ -42,6 +42,7 @@
 import org.eclipse.jdt.internal.core.JavaProject;
 import org.eclipse.jdt.internal.core.builder.SourceFile;
 
+import com.sun.tools.javac.api.MultiTaskListener;
 import com.sun.tools.javac.comp.*;
 import com.sun.tools.javac.comp.CompileStates.CompileState;
 import com.sun.tools.javac.main.JavaCompiler;
@@ -100,6 +101,12 @@ public void compile(ICompilationUnit[] sourceUnits) {
 				return true;
 			})
 			.collect(Collectors.groupingBy(this::computeOutputDirectory));
+
+		// Register listener to intercept intermediate results from Javac task.
+		JavacTaskListener resultListener = new JavacTaskListener(this.compilerConfig, outputSourceMapping);
+		MultiTaskListener mtl = MultiTaskListener.instance(javacContext);
+		mtl.add(resultListener);
+
 		for (Entry<File, List<ICompilationUnit>> outputSourceSet : outputSourceMapping.entrySet()) {
 			var outputFile = outputSourceSet.getKey();
 			JavacUtils.configureJavacContext(javacContext, this.compilerConfig, javaProject, outputFile);

org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacConfig.java

@@ -57,7 +57,11 @@ public record JavacConfig(
 	 * The compiler options used to control the compilation behavior.
 	 * See {@link org.eclipse.jdt.internal.compiler.impl.CompilerOptions} for a list of available options.
 	 */
-	CompilerOptions compilerOptions) {
+	CompilerOptions compilerOptions,
+	/**
+	 * A reference to the original config
+	 */
+	CompilerConfiguration originalConfig) {
 
 	static JavacConfig createFrom(CompilerConfiguration config) {
 		return new JavacConfig(
@@ -68,6 +72,7 @@ static JavacConfig createFrom(CompilerConfiguration config) {
 			config.annotationProcessorPaths().stream().map(URI::getPath).collect(Collectors.toList()),
 			config.generatedSourcePaths().stream().map(IContainer::getRawLocation).filter(path -> path != null).map(IPath::toOSString).collect(Collectors.toList()),
 			config.sourceOutputMapping().entrySet().stream().collect(Collectors.toMap(e -> e.getKey().getRawLocation().toFile(), e -> e.getValue().getRawLocation().toFile())),
-			config.compilerOptions());
+			config.compilerOptions(),
+			config);
 	}
 }

org.eclipse.jdt.core.javac/src/org/eclipse/jdt/internal/javac/JavacTaskListener.java

@@ -0,0 +1,76 @@
+/*******************************************************************************
+* Copyright (c) 2024 Microsoft Corporation and others.
+* All rights reserved. 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:
+*     Microsoft Corporation - initial API and implementation
+*******************************************************************************/
+
+package org.eclipse.jdt.internal.javac;
+
+import java.io.File;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.stream.Collectors;
+
+import javax.lang.model.element.TypeElement;
+
+import org.eclipse.core.resources.IContainer;
+import org.eclipse.core.resources.IFile;
+import org.eclipse.core.resources.IResource;
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.core.runtime.IPath;
+import org.eclipse.core.runtime.Path;
+import org.eclipse.jdt.internal.compiler.env.ICompilationUnit;
+import org.eclipse.jdt.internal.compiler.util.SuffixConstants;
+
+import com.sun.source.util.TaskEvent;
+import com.sun.source.util.TaskListener;
+import com.sun.tools.javac.code.Symbol.ClassSymbol;
+
+public class JavacTaskListener implements TaskListener {
+	private Map<ICompilationUnit, IContainer> sourceOutputMapping = new HashMap<>();
+
+	public JavacTaskListener(JavacConfig config, Map<File, List<ICompilationUnit>> outputSourceMapping) {
+		Map<File, IContainer> outputs = config.originalConfig().sourceOutputMapping().values().stream()
+				.distinct().filter(container -> container.getRawLocation() != null)
+				.collect(Collectors.toMap(container -> container.getRawLocation().toFile(), container -> container));
+		for (Entry<File, List<ICompilationUnit>> entry : outputSourceMapping.entrySet()) {
+			if (outputs.containsKey(entry.getKey())) {
+				IContainer currentOutput = outputs.get(entry.getKey());
+				entry.getValue().forEach(cu -> sourceOutputMapping.put(cu, currentOutput));
+			}
+		}
+	}
+
+	@Override
+	public void finished(TaskEvent e) {
+		if (e.getKind() == TaskEvent.Kind.GENERATE) {
+			if (e.getSourceFile() instanceof JavacFileObject sourceFile) {
+				ICompilationUnit originalUnit = sourceFile.getOriginalUnit();
+				IContainer outputDir = this.sourceOutputMapping.get(originalUnit);
+				if (outputDir != null) {
+					TypeElement element = e.getTypeElement();
+					if (element instanceof ClassSymbol clazz) {
+						String fileName = clazz.flatName().toString().replace('.', File.separatorChar);
+						IPath filePath = new Path(fileName);
+						IFile classFile = outputDir.getFile(filePath.addFileExtension(SuffixConstants.EXTENSION_class));
+						try {
+							// refresh the class file to make sure it is visible in the Eclipse workspace
+							classFile.refreshLocal(IResource.DEPTH_ZERO, null);
+						} catch (CoreException e1) {
+							// TODO error handling
+						}
+					}
+				}
+			}
+		}
+	}
+}