Fix CSA kotlin issue

Author: Laurens-W

src/main/java/org/openrewrite/staticanalysis/CovariantEquals.java

@@ -65,7 +65,16 @@ public TreeVisitor<?, ExecutionContext> getVisitor() {
             @Override
             public J.MethodDeclaration visitMethodDeclaration(J.MethodDeclaration method, ExecutionContext ctx) {
                 J.MethodDeclaration m = super.visitMethodDeclaration(method, ctx);
-                J.ClassDeclaration enclosingClass = getCursor().dropParentUntil(p -> p instanceof J.ClassDeclaration).getValue();
+
+                // Find the enclosing type declaration - could be class, interface, enum, etc.
+                // For Kotlin, methods might be top-level (no class parent at all)
+                Object parent = getCursor().getParent(J.ClassDeclaration.class);
+                if (parent == null) {
+                    // Not in a J.ClassDeclaration - could be interface, enum, or Kotlin structure
+                    return m;
+                }
+
+                J.ClassDeclaration enclosingClass = (J.ClassDeclaration) parent;
 
                 /*
                  * Looking for "public boolean equals(EnclosingClassType)" as the method signature match.

src/test/java/org/openrewrite/staticanalysis/kotlin/CovariantEqualsTest.java

@@ -0,0 +1,175 @@
+/*
+ * Copyright 2024 the original author or authors.
+ * <p>
+ * Licensed under the Moderne Source Available License (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://docs.moderne.io/licensing/moderne-source-available-license
+ * <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.staticanalysis.kotlin;
+
+import org.junit.jupiter.api.Test;
+import org.openrewrite.Issue;
+import org.openrewrite.staticanalysis.CovariantEquals;
+import org.openrewrite.test.RecipeSpec;
+import org.openrewrite.test.RewriteTest;
+
+import static org.openrewrite.kotlin.Assertions.kotlin;
+
+class CovariantEqualsTest implements RewriteTest {
+
+    @Override
+    public void defaults(RecipeSpec spec) {
+        spec.recipe(new CovariantEquals());
+    }
+
+    @Test
+    void topLevelFunctionDoesNotCrash() {
+        // This test verifies that the recipe doesn't crash when encountering a top-level Kotlin function
+        // Top-level functions don't have a class parent, which was causing the dropParentUntil error
+        rewriteRun(
+          kotlin(
+            """
+              // Top-level equals function - should not cause a crash
+              fun equals(other: String): Boolean {
+                  return false
+              }
+
+              fun main() {
+                  println("Test")
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinClassWithCovariantEquals() {
+        // Test that Kotlin classes with covariant equals are left unchanged
+        // (Kotlin has its own mechanisms for handling equals)
+        rewriteRun(
+          kotlin(
+            """
+              class Test {
+                  var n: Int = 0
+
+                  fun equals(other: Test): Boolean {
+                      return n == other.n
+                  }
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinDataClassUnchanged() {
+        // Data classes have compiler-generated equals methods
+        rewriteRun(
+          kotlin(
+            """
+              data class Person(val name: String, val age: Int)
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinInterfaceWithEquals() {
+        // Test that interfaces with equals methods don't cause crashes
+        rewriteRun(
+          kotlin(
+            """
+              interface TestInterface {
+                  fun equals(other: TestInterface): Boolean
+              }
+
+              class TestImpl : TestInterface {
+                  override fun equals(other: TestInterface): Boolean {
+                      return true
+                  }
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinObjectDeclaration() {
+        // Test that object declarations (singletons) don't cause crashes
+        rewriteRun(
+          kotlin(
+            """
+              object Singleton {
+                  fun equals(other: Singleton): Boolean {
+                      return true
+                  }
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinEnumWithEquals() {
+        // Test that enum classes with equals methods don't cause crashes
+        rewriteRun(
+          kotlin(
+            """
+              enum class Color {
+                  RED, GREEN, BLUE;
+
+                  fun equals(other: Color): Boolean {
+                      return this == other
+                  }
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinNestedClassWithEquals() {
+        // Test nested classes with equals methods
+        rewriteRun(
+          kotlin(
+            """
+              class Outer {
+                  class Inner {
+                      var value: Int = 0
+
+                      fun equals(other: Inner): Boolean {
+                          return value == other.value
+                      }
+                  }
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void kotlinCompanionObjectWithEquals() {
+        // Test companion objects with equals methods
+        rewriteRun(
+          kotlin(
+            """
+              class MyClass {
+                  companion object {
+                      fun equals(other: MyClass): Boolean {
+                          return false
+                      }
+                  }
+              }
+              """
+          )
+        );
+    }
+}