feat: Add RemoveUnusedDeclarations

lib/src/main/java/com/diffplug/spotless/java/RemoveUnusedDeclarationsStep.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2016-2025 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.spotless.java;
+
+import com.diffplug.spotless.FormatterStep;
+import com.diffplug.spotless.glue.pjf.PalantirJavaFormatFormatterFormatSourceAndFixImportsAndDeclarationsFunc;
+import com.diffplug.spotless.glue.pjf.PalantirJavaFormatFormatterFunc;
+
+/** Uses google-java-format or cleanthat.UnnecessaryImport, but only to remove unused imports. */
+public interface RemoveUnusedDeclarationsStep {
+	String NAME = "removeUnusedImports";
+
+	static FormatterStep create() {
+		return new PalantirJavaFormatFormatterFormatSourceAndFixImportsAndDeclarationsFunc("PALANTIR", true);
+	}
+}

lib/src/palantirJavaFormat/java/com/diffplug/spotless/glue/pjf/PalantirJavaFormatFormatterFormatSourceAndFixImportsAndDeclarationsFunc.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright 2022-2025 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.spotless.glue.pjf;
+
+import java.io.File;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.List;
+
+import javax.annotation.Nullable;
+
+import com.palantir.javaformat.java.Formatter;
+import com.palantir.javaformat.java.ImportOrderer;
+import com.palantir.javaformat.java.JavaFormatterOptions;
+import com.palantir.javaformat.java.RemoveUnusedImports;
+
+import com.diffplug.spotless.FormatterFunc;
+import com.diffplug.spotless.FormatterStep;
+import com.diffplug.spotless.Lint;
+
+public class PalantirJavaFormatFormatterFormatSourceAndFixImportsAndDeclarationsFunc implements FormatterFunc, FormatterStep {
+
+	private final Formatter formatter;
+
+	private final JavaFormatterOptions.Style formatterStyle;
+
+	/**
+	 * Creates a new formatter func that formats code via Palantir.
+	 * @param style The style to use for formatting.
+	 * @param formatJavadoc Whether to format Java docs. Requires at least Palantir 2.36.0 or later, otherwise the
+	 * constructor will throw.
+	 */
+	public PalantirJavaFormatFormatterFormatSourceAndFixImportsAndDeclarationsFunc(String style, boolean formatJavadoc) {
+		this.formatterStyle = JavaFormatterOptions.Style.valueOf(style);
+		JavaFormatterOptions.Builder builder = JavaFormatterOptions.builder();
+		builder.style(formatterStyle);
+		if (formatJavadoc) {
+			applyFormatJavadoc(builder);
+		}
+		formatter = Formatter.createFormatter(builder.build());
+	}
+
+	@Override
+	public String apply(String input) throws Exception {
+		return formatter.formatSourceAndFixImportsAndDeclarations(input);
+	}
+
+	@Override
+	public String apply(String unix, File file) throws Exception {
+		return FormatterFunc.super.apply(unix, file);
+	}
+
+	@Override
+	public List<Lint> lint(String content, File file) throws Exception {
+		return FormatterFunc.super.lint(content, file);
+	}
+
+	@Override
+	public String toString() {
+		return "PalantirJavaFormatFormatterFunc{formatter=" + formatter + '}';
+	}
+
+	private static void applyFormatJavadoc(JavaFormatterOptions.Builder builder) {
+		// The formatJavadoc option is available since Palantir 2.36.0
+		// To support older versions for now, attempt to invoke the builder method via reflection.
+		try {
+			Method formatJavadoc = JavaFormatterOptions.Builder.class.getMethod("formatJavadoc", boolean.class);
+			formatJavadoc.invoke(builder, true);
+		} catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
+			throw new IllegalStateException("Cannot enable formatJavadoc option, make sure you are using Palantir with version 2.36.0 or later", e);
+		}
+	}
+
+	@Override
+	public String getName() {
+		return toString();
+	}
+
+	@Nullable @Override
+	public String format(String rawUnix, File file) throws Exception {
+		return apply(rawUnix);
+	}
+
+	@Override
+	public void close() throws Exception {
+
+	}
+}

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/JavaExtension.java

@@ -40,6 +40,7 @@
 import com.diffplug.spotless.java.GoogleJavaFormatStep;
 import com.diffplug.spotless.java.ImportOrderStep;
 import com.diffplug.spotless.java.PalantirJavaFormatStep;
+import com.diffplug.spotless.java.RemoveUnusedDeclarationsStep;
 import com.diffplug.spotless.java.RemoveUnusedImportsStep;
 import com.diffplug.spotless.java.RemoveWildcardImportsStep;
 
@@ -156,6 +157,10 @@ public void removeWildcardImports() {
 		addStep(RemoveWildcardImportsStep.create());
 	}
 
+	public void removeUnusedDeclarations() {
+		addStep(RemoveUnusedDeclarationsStep.create());
+	}
+
 	/** Uses the <a href="https://github.com/google/google-java-format">google-java-format</a> jar to format source code. */
 	public GoogleJavaFormatConfig googleJavaFormat() {
 		return googleJavaFormat(GoogleJavaFormatStep.defaultVersion());