Add suppression support to UnusedPropertyRule

pom.xml

@@ -17,6 +17,7 @@
         <skipChecks>${skipTests}</skipChecks>
 
         <pmd.version>7.22.0</pmd.version>
+        <!--suppress MavenModelInspection -->
         <junit.version>6.0.3</junit.version>
     </properties>
 

src/main/java/com/solubris/enforcer/UnusedPropertyRule.java

@@ -7,10 +7,15 @@
 
 import javax.inject.Inject;
 import javax.inject.Named;
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 import java.util.concurrent.atomic.LongAdder;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -24,23 +29,37 @@
  * Ensures that version properties are used.
  *
  * <p>This catches the typical scenario where a dependency is removed, but the property left orphaned.
+ *
+ * <p>Suppression: add a comment on the line before the property, e.g. {@code <!-- suppress UnusedProperty -->}
  */
 @Named("unusedPropertyRule")
 public class UnusedPropertyRule extends AbstractEnforcerRule {
     private static final Pattern PROPERTY_PATTERN = Pattern.compile("\\$\\{([^}]+)\\}");
+    private static final Pattern SUPPRESS_COMMENT = Pattern.compile("<!--\\s*suppress\\s+UnusedProperty\\s*-->", Pattern.CASE_INSENSITIVE);
+    private static final Pattern PROPERTY_ELEMENT = Pattern.compile("<([a-zA-Z0-9.-]+)>");
 
     private final Model originalModel;
     private final Model effectiveModel;
+    private final Set<String> suppressedProperties;
 
     @SuppressWarnings("unused")
     @Inject
     public UnusedPropertyRule(MavenSession session) {
-        this(ModelScanner.modelFrom(session), session.getCurrentProject().getModel());
+        this(
+                ModelScanner.modelFrom(session),
+                session.getCurrentProject().getModel(),
+                parseSuppressions(session.getCurrentProject().getFile())
+        );
     }
 
     protected UnusedPropertyRule(Model originalModel, Model effectiveModel) {
+        this(originalModel, effectiveModel, Collections.emptySet());
+    }
+
+    protected UnusedPropertyRule(Model originalModel, Model effectiveModel, Set<String> suppressedProperties) {
         this.originalModel = originalModel;
         this.effectiveModel = effectiveModel;
+        this.suppressedProperties = suppressedProperties != null ? suppressedProperties : Collections.emptySet();
     }
 
     @Override
@@ -68,6 +87,7 @@ protected Stream<String> scanProperties() {
 
         return originalModel.getProperties().entrySet().stream()
                 .filter(UnusedPropertyRule::isVersionProperty) // only check properties that look like versions
+                .filter(e -> !suppressedProperties.contains(e.getKey().toString()))
                 .map(e -> {
                     String propName = e.getKey().toString();
                     String propValue = e.getValue() != null ? e.getValue().toString() : "";
@@ -76,6 +96,43 @@ protected Stream<String> scanProperties() {
                 }).filter(Objects::nonNull);
     }
 
+    /**
+     * Parses the pom file for suppression comments on the line before property elements.
+     * Format: {@code <!-- suppress UnusedProperty -->} on the line immediately before the property.
+     */
+    static Set<String> parseSuppressions(File pomFile) {
+        if (pomFile == null || !pomFile.isFile()) {
+            return Collections.emptySet();
+        }
+        try {
+            List<String> lines = Files.readAllLines(pomFile.toPath());
+            Set<String> suppressed = new HashSet<>();
+            boolean inProperties = false;
+            for (int i = 0; i < lines.size(); i++) {
+                String line = lines.get(i);
+                if (line.contains("<properties>")) {
+                    inProperties = true;
+                    continue;
+                }
+                if (inProperties && line.contains("</properties>")) {
+                    break;
+                }
+                if (inProperties && i > 0) {
+                    var matcher = PROPERTY_ELEMENT.matcher(line);
+                    if (matcher.find() && matcher.start() == line.indexOf("<")) {
+                        String prevLine = lines.get(i - 1);
+                        if (SUPPRESS_COMMENT.matcher(prevLine).find()) {
+                            suppressed.add(matcher.group(1));
+                        }
+                    }
+                }
+            }
+            return suppressed;
+        } catch (IOException e) {
+            return Collections.emptySet();
+        }
+    }
+
     private static boolean isVersionProperty(Map.Entry<Object, Object> e) {
         return e.getKey().toString().endsWith(".version");
     }

src/test/java/com/solubris/enforcer/UnusedPropertyRuleTest.java

@@ -9,7 +9,12 @@
 import org.apache.maven.model.PluginManagement;
 import org.apache.maven.model.Reporting;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Set;
 import java.util.stream.Stream;
 
 import static com.solubris.enforcer.ModelStubber.dependencyOf;
@@ -203,6 +208,36 @@ void executePassesWhenAllPropertiesUsed() {
         assertThatNoException().isThrownBy(rule::execute);
     }
 
+    @Test
+    void suppressedUnusedPropertyPasses() {
+        originalModel.addProperty("kept-for-compat.version", "1.0.0");
+        UnusedPropertyRule ruleWithSuppression = new UnusedPropertyRule(
+                originalModel, effectiveModel, Set.of("kept-for-compat.version"));
+        ruleWithSuppression.setLog(mock(EnforcerLogger.class));
+
+        Stream<String> violations = ruleWithSuppression.scanProperties();
+
+        assertThat(violations).isEmpty();
+    }
+
+    @Test
+    void parseSuppressions_readsCommentFromPom(@TempDir Path tempDir) throws IOException {
+        Path pom = tempDir.resolve("pom.xml");
+        Files.writeString(pom, """
+            <project>
+                <properties>
+                    <used.version>1.0</used.version>
+                    <!-- suppress UnusedProperty -->
+                    <suppressed.version>2.0</suppressed.version>
+                </properties>
+            </project>
+            """);
+
+        Set<String> suppressed = UnusedPropertyRule.parseSuppressions(pom.toFile());
+
+        assertThat(suppressed).containsExactly("suppressed.version");
+    }
+
     @Test
     void versionPropertyUsedByPluginDependencyPasses() {
         originalModel.addProperty("api.version", "3.0.0");