Support Checkstyle UnusedImports (#5389)

* Support Checkstyle UnusedImports

* add additional test case

---------

Co-authored-by: Sergii Melnyk <smelnik@playtika.com>
Co-authored-by: Merlin Bögershausen <merlin.boegershausen@rwth-aachen.de>

Author: 3 people

rewrite-java/src/main/java/org/openrewrite/java/style/Checkstyle.java

@@ -54,7 +54,8 @@ private Checkstyle() {
                         operatorWrapStyle(),
                         typecastParenPadStyle(),
                         unnecessaryParentheses(),
-                        customImportOrderStyle()
+                        customImportOrderStyle(),
+                        unusedImportsStyle()
                 ));
     }
 
@@ -155,4 +156,8 @@ public static CustomImportOrderStyle customImportOrderStyle() {
                 new CustomImportOrderStyle.GroupWithDepth(CustomImportOrderStyle.CustomImportOrderGroup.THIRD_PARTY_PACKAGE, null)),
                 true, false, "^$", "^(java|javax)\\.", ".*");
     }
+
+    private static UnusedImportsStyle unusedImportsStyle() {
+        return new UnusedImportsStyle(false);
+    }
 }

rewrite-java/src/main/java/org/openrewrite/java/style/CheckstyleConfigLoader.java

@@ -78,7 +78,8 @@ public static Checkstyle loadCheckstyleConfig(InputStream checkstyleConf, Map<St
                                 operatorWrapStyle(conf),
                                 typecastParenPadStyle(conf),
                                 unnecessaryParentheses(conf),
-                                customImportOrderStyle(conf))
+                                customImportOrderStyle(conf),
+                                unusedImportsStyles(conf))
                         .filter(Objects::nonNull)
                         .flatMap(Set::stream)
                         .collect(toSet()));
@@ -532,6 +533,16 @@ public static Checkstyle loadCheckstyleConfig(InputStream checkstyleConf, Map<St
                 .collect(Collectors.toSet());
     }
 
+    private static @Nullable Set<UnusedImportsStyle> unusedImportsStyles(Map<String, List<Module>> conf) {
+        List<Module> moduleList = conf.get("UnusedImports");
+        if (moduleList == null) {
+            return null;
+        }
+        return moduleList.stream()
+            .map(module -> new UnusedImportsStyle(parseBoolean(module.properties.get("processJavadoc"))))
+            .collect(toSet());
+    }
+
     protected static class Module {
         private final String name;
         private final Map<String, String> properties;

rewrite-java/src/main/java/org/openrewrite/java/style/UnusedImportsStyle.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2025 the original author or authors.
+ * <p>
+ * 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
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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 org.openrewrite.java.style;
+
+import lombok.Value;
+import lombok.With;
+import org.openrewrite.java.JavaStyle;
+
+@Value
+@With
+public class UnusedImportsStyle implements JavaStyle {
+
+    /**
+     * Control whether to process Javadoc comments.
+     */
+    boolean processJavadoc;
+}

rewrite-java/src/test/java/org/openrewrite/java/style/CheckstyleConfigLoaderTest.java

@@ -363,4 +363,65 @@ void customImportOrderStyle() throws CheckstyleException {
           new CustomImportOrderStyle.GroupWithDepth(CustomImportOrderStyle.CustomImportOrderGroup.SPECIAL_IMPORTS, null),
           new CustomImportOrderStyle.GroupWithDepth(CustomImportOrderStyle.CustomImportOrderGroup.STATIC, null));
     }
+
+    @Test
+    void unusedImportsWithJavadocProcessing() throws CheckstyleException {
+        var checkstyle = loadCheckstyleConfig("""
+            <!DOCTYPE module PUBLIC
+                "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
+                "https://checkstyle.org/dtds/configuration_1_2.dtd">
+            <module name="Checker">
+                <module name="TreeWalker">
+                    <module name="UnusedImports">
+                        <property name="processJavadoc" value="true"/>
+                    </module>
+                </module>
+            </module>
+        """, emptyMap());
+
+        assertThat(checkstyle.getStyles()).hasSize(1).allSatisfy(style -> {
+            assertThat(style).isInstanceOf(UnusedImportsStyle.class);
+            assertThat(((UnusedImportsStyle) style).isProcessJavadoc()).isTrue();
+        });
+    }
+
+    @Test
+    void unusedImportsWithoutExpliciteJavadocProcessing() throws CheckstyleException {
+        var checkstyle = loadCheckstyleConfig("""
+            <!DOCTYPE module PUBLIC
+                "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
+                "https://checkstyle.org/dtds/configuration_1_2.dtd">
+            <module name="Checker">
+                <module name="TreeWalker">
+                    <module name="UnusedImports">
+                        <property name="processJavadoc" value="false"/>
+                    </module>
+                </module>
+            </module>
+        """, emptyMap());
+
+        assertThat(checkstyle.getStyles()).hasSize(1).allSatisfy(style -> {
+            assertThat(style).isInstanceOf(UnusedImportsStyle.class);
+            assertThat(((UnusedImportsStyle) style).isProcessJavadoc()).isFalse();
+        });
+    }
+
+    @Test
+    void unusedImportsWithoutJavadocProcessing() throws CheckstyleException {
+        var checkstyle = loadCheckstyleConfig("""
+            <!DOCTYPE module PUBLIC
+                "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
+                "https://checkstyle.org/dtds/configuration_1_2.dtd">
+            <module name="Checker">
+                <module name="TreeWalker">
+                    <module name="UnusedImports"/>
+                </module>
+            </module>
+        """, emptyMap());
+
+        assertThat(checkstyle.getStyles()).hasSize(1).allSatisfy(style -> {
+            assertThat(style).isInstanceOf(UnusedImportsStyle.class);
+            assertThat(((UnusedImportsStyle) style).isProcessJavadoc()).isFalse();
+        });
+    }
 }