Add code action for unused pattern variable / unused lambda parameter.

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/cleanup/CleanUpRegistry.java

@@ -55,7 +55,8 @@ public CleanUpRegistry() {
 			new LambdaExpressionCleanup(),
 			new TryWithResourceCleanUp(),
 			new LambdaExpressionAndMethodRefCleanUp(),
-			new OrganizeImportsCleanup());
+			new OrganizeImportsCleanup(),
+			new RenameUnusedLocalVariableCleanup());
 
 		// Store in a Map so that they can be accessed by ID quickly
 		cleanUps = new HashMap<>();

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/cleanup/RenameUnusedLocalVariableCleanup.java

@@ -0,0 +1,49 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Red Hat Inc. 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
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Red Hat Inc. - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.jdt.ls.core.internal.cleanup;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.jdt.core.JavaCore;
+import org.eclipse.jdt.internal.corext.fix.CleanUpConstants;
+import org.eclipse.jdt.internal.corext.fix.RenameUnusedVariableFixCore;
+import org.eclipse.jdt.ui.cleanup.CleanUpContext;
+import org.eclipse.jdt.ui.cleanup.ICleanUpFix;
+
+/**
+ * Represents a clean up that renames unused lambda parameter identifier to an
+ * underscore (_)
+ */
+public class RenameUnusedLocalVariableCleanup implements ISimpleCleanUp {
+
+	private static final List<String> COMPILER_OPTS = Arrays.asList(JavaCore.COMPILER_PB_UNUSED_LAMBDA_PARAMETER, JavaCore.COMPILER_PB_UNUSED_LOCAL);
+
+	@Override
+	public Collection<String> getIdentifiers() {
+		return List.of("removeUnusedLambdaParameters", CleanUpConstants.REMOVE_UNUSED_CODE_LOCAL_VARIABLES);
+	}
+
+	@Override
+	public ICleanUpFix createFix(CleanUpContext context) throws CoreException {
+		return RenameUnusedVariableFixCore.createCleanUp(context.getAST(), true);
+	}
+
+	@Override
+	public List<String> getRequiredCompilerMarkers() {
+		return COMPILER_OPTS;
+	}
+
+}

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/corrections/QuickFixProcessor.java

@@ -342,6 +342,7 @@ private void process(CodeActionParams params, IInvocationContext context, IProbl
 			case IProblem.UnusedPrivateType:
 			case IProblem.LocalVariableIsNeverUsed:
 			case IProblem.ArgumentIsNeverUsed:
+			case IProblem.LambdaParameterIsNeverUsed:
 			case IProblem.UnusedPrivateField:
 				LocalCorrectionsSubProcessor.addUnusedMemberProposal(context, problem, proposals);
 				break;

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/corrections/proposals/LocalCorrectionsSubProcessor.java

@@ -92,6 +92,7 @@
 import org.eclipse.jdt.internal.corext.fix.CleanUpConstants;
 import org.eclipse.jdt.internal.corext.fix.CodeStyleFixCore;
 import org.eclipse.jdt.internal.corext.fix.IProposableFix;
+import org.eclipse.jdt.internal.corext.fix.RenameUnusedVariableFixCore;
 import org.eclipse.jdt.internal.corext.fix.SealedClassFixCore;
 import org.eclipse.jdt.internal.corext.fix.UnimplementedCodeFixCore;
 import org.eclipse.jdt.internal.corext.fix.UnusedCodeFixCore;
@@ -434,6 +435,22 @@ public static void addUnimplementedMethodsProposals(IInvocationContext context,
 	public static void addUnusedMemberProposal(IInvocationContext context, IProblemLocation problem, Collection<ProposalKindWrapper> proposals) {
 		int problemId = problem.getProblemId();
 
+		if (JavaModelUtil.is22OrHigher(context.getCompilationUnit().getJavaProject()) && (problemId == IProblem.LocalVariableIsNeverUsed || problemId == IProblem.LambdaParameterIsNeverUsed)) {
+			RenameUnusedVariableFixCore fix = RenameUnusedVariableFixCore.createRenameToUnnamedFix(context.getASTRoot(), problem);
+			if (fix != null) {
+				try {
+					CompilationUnitChange change = fix.createChange(null);
+					CUCorrectionProposalCore proposal = new CUCorrectionProposalCore(change.getName(), change.getCompilationUnit(), change, IProposalRelevance.UNUSED_MEMBER);
+					proposals.add(CodeActionHandler.wrap(proposal, CodeActionKind.QuickFix));
+				} catch (CoreException e) {
+					JavaLanguageServerPlugin.log(e);
+				}
+			}
+		}
+		if (problemId == IProblem.LambdaParameterIsNeverUsed) {
+			return;
+		}
+
 		UnusedCodeFixCore fix = UnusedCodeFixCore.createUnusedMemberFix(context.getASTRoot(), problem, false);
 		if (fix != null) {
 			try {

org.eclipse.jdt.ls.tests/src/org/eclipse/jdt/ls/core/internal/cleanup/CleanUpsTest.java

@@ -58,7 +58,7 @@ public void setup() throws Exception {
 		javaProject = JavaCore.create(project);
 
 		Hashtable<String, String> options = TestOptions.getDefaultOptions();
-		JavaCore.setComplianceOptions(JavaCore.VERSION_19, options);
+		JavaCore.setComplianceOptions(JavaCore.VERSION_22, options);
 		options.put(DefaultCodeFormatterConstants.FORMATTER_NUMBER_OF_EMPTY_LINES_TO_PRESERVE, String.valueOf(99));
 		javaProject.setOptions(options);
 
@@ -640,4 +640,39 @@ public void test() {
 		assertEquals(expected, actual);
 	}
 
+	@Test
+	public void testRenameUnusedLambdaParameterCleanup() throws Exception {
+		String contents = """
+				package test1;
+				public class A {
+				    private interface J {
+					    public void run(String a, String b);
+				    }
+				    public void test() {
+				        J j = (a, b) -> System.out.println(a);
+					    j.run("a", "b");
+				    }
+				}
+				""";
+
+		ICompilationUnit unit = pack1.createCompilationUnit("A.java", contents, false, monitor);
+		String uri = unit.getUnderlyingResource().getLocationURI().toString();
+
+		String expected = """
+				package test1;
+				public class A {
+				    private interface J {
+					    public void run(String a, String b);
+				    }
+				    public void test() {
+				        J j = (a, _) -> System.out.println(a);
+					    j.run("a", "b");
+				    }
+				}
+				""";
+		List<TextEdit> textEdits = registry.getEditsForAllActiveCleanUps(new TextDocumentIdentifier(uri), Arrays.asList("removeUnusedLambdaParameters"), monitor);
+		String actual = TextEditUtil.apply(unit, textEdits);
+		assertEquals(expected, actual);
+	}
+
 }