Issue #11604: allows 3rd parties to expand module identification

src/main/java/com/puppycrawl/tools/checkstyle/utils/ModuleReflectionUtil.java

@@ -24,6 +24,7 @@
 import java.lang.reflect.Modifier;
 import java.util.Collection;
 import java.util.Set;
+import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
 import com.google.common.reflect.ClassPath;
@@ -41,10 +42,43 @@
  */
 public final class ModuleReflectionUtil {
 
+    /** Default identification predicate. */
+    private static final Predicate<Class<?>> DEFAULT_IDENTIFICATION_PREDICATE = clazz -> {
+        return isCheckstyleTreeWalkerCheck(clazz)
+                || isFileSetModule(clazz)
+                || isFilterModule(clazz)
+                || isFileFilterModule(clazz)
+                || isTreeWalkerFilterModule(clazz)
+                || isAuditListener(clazz)
+                || isRootModule(clazz);
+    };
+
+    /** Current identification predicate. */
+    private static Predicate<Class<?>> identificationPredicate = DEFAULT_IDENTIFICATION_PREDICATE;
+
     /** Prevent instantiation. */
     private ModuleReflectionUtil() {
     }
 
+    /**
+     * Allows Checkstyle to understand more modules to work with it via a
+     * predicate. This creates a chain of predicates for identification
+     * purposes. If a prior predicate fails to identify a module, it will
+     * continue next on the chain until all say the class cannot be identified.
+     *
+     * @param newPredicate The provided predicate that will return {@code true}
+     *        if the class given to it is identified as a type of module,
+     *        otherwise {@code false} if it does not.
+     */
+    public static void addNewModuleIdentification(Predicate<Class<?>> newPredicate) {
+        identificationPredicate = newPredicate.or(identificationPredicate);
+    }
+
+    /** Resets the identification process Checkstyle uses to know if a class is a module. */
+    public static void resetIdentification() {
+        identificationPredicate = DEFAULT_IDENTIFICATION_PREDICATE;
+    }
+
     /**
      * Gets checkstyle's modules (directly, not recursively) in the given packages.
      *
@@ -74,13 +108,7 @@ public static Set<Class<?>> getCheckstyleModules(
      */
     public static boolean isCheckstyleModule(Class<?> clazz) {
         return isValidCheckstyleClass(clazz)
-            && (isCheckstyleTreeWalkerCheck(clazz)
-                    || isFileSetModule(clazz)
-                    || isFilterModule(clazz)
-                    || isFileFilterModule(clazz)
-                    || isTreeWalkerFilterModule(clazz)
-                    || isAuditListener(clazz)
-                    || isRootModule(clazz));
+            && identificationPredicate.test(clazz);
     }
 
     /**

src/test/java/com/puppycrawl/tools/checkstyle/utils/ModuleReflectionUtilTest.java

@@ -179,6 +179,29 @@ public void testKeepEclipseHappy() {
             .isEqualTo(1);
     }
 
+    @Test
+    public void testIdentification() {
+        assertWithMessage("Should return false when invalid class is passed by default")
+            .that(ModuleReflectionUtil
+                .isCheckstyleModule(InvalidWithDefaultConstructorClass.class))
+            .isFalse();
+
+        ModuleReflectionUtil.addNewModuleIdentification(
+                clazz -> clazz == InvalidWithDefaultConstructorClass.class);
+
+        assertWithMessage("Should return true with a new identification")
+            .that(ModuleReflectionUtil
+                .isCheckstyleModule(InvalidWithDefaultConstructorClass.class))
+            .isTrue();
+
+        ModuleReflectionUtil.resetIdentification();
+
+        assertWithMessage("Should return false when identification is reset")
+            .that(ModuleReflectionUtil
+                .isCheckstyleModule(InvalidWithDefaultConstructorClass.class))
+            .isFalse();
+    }
+
     private static class ValidCheckstyleClass extends AutomaticBean {
 
         // empty, use default constructor
@@ -380,4 +403,12 @@ protected void finishLocalSetup() {
 
     }
 
+    private static class InvalidWithDefaultConstructorClass extends AutomaticBean {
+        @Override
+        protected void finishLocalSetup() {
+            // dummy method
+        }
+
+    }
+
 }