Fix regression in reflection on looking up equals/hashCode/toString in interface

Caused by 4266e50be8 and 8ccbbf71ec. Previously it worked because we
used hardcoded signatures of equals/hashCode/toString and always looked
them up in java.lang.Object

 #KT-25404 Fixed

compiler/testData/codegen/box/reflection/mapping/methodsFromObject.kt

@@ -0,0 +1,37 @@
+// TARGET_BACKEND: JVM
+// WITH_REFLECT
+
+import kotlin.reflect.KClass
+import kotlin.reflect.full.memberFunctions
+import kotlin.reflect.jvm.javaMethod
+import kotlin.test.assertEquals
+
+annotation class A
+interface I
+class C
+
+interface MyCustomMembers {
+    fun equals(): Boolean
+    fun hashCode(hehe: Int): Int
+    fun toString(hehe: String): Any
+}
+
+interface MyCloneable : Cloneable
+
+fun KClass<*>.functions() = memberFunctions.map { it.javaMethod!!.name }.sorted()
+
+fun box(): String {
+    assertEquals(listOf("equals", "hashCode", "toString"), A::class.functions())
+    assertEquals(listOf("equals", "hashCode", "toString"), I::class.functions())
+    assertEquals(listOf("equals", "hashCode", "toString"), C::class.functions())
+
+    assertEquals(
+        listOf("equals", "equals", "hashCode", "hashCode", "toString", "toString"),
+        MyCustomMembers::class.functions()
+    )
+
+    // TODO: KT-22923
+    // assertEquals(listOf("clone", "equals", "hashCode", "toString"), MyCloneable::class.functions())
+
+    return "OK"
+}

compiler/tests-ir-jvm/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -17633,6 +17633,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/reflection/mapping/memberProperty.kt");
             }
 
+            @TestMetadata("methodsFromObject.kt")
+            public void testMethodsFromObject() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/mapping/methodsFromObject.kt");
+            }
+
             @TestMetadata("openSuspendFun.kt")
             public void testOpenSuspendFun() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/mapping/openSuspendFun.kt");

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -17633,6 +17633,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/reflection/mapping/memberProperty.kt");
             }
 
+            @TestMetadata("methodsFromObject.kt")
+            public void testMethodsFromObject() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/mapping/methodsFromObject.kt");
+            }
+
             @TestMetadata("openSuspendFun.kt")
             public void testOpenSuspendFun() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/mapping/openSuspendFun.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -17633,6 +17633,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/reflection/mapping/memberProperty.kt");
             }
 
+            @TestMetadata("methodsFromObject.kt")
+            public void testMethodsFromObject() throws Exception {
+                runTest("compiler/testData/codegen/box/reflection/mapping/methodsFromObject.kt");
+            }
+
             @TestMetadata("openSuspendFun.kt")
             public void testOpenSuspendFun() throws Exception {
                 runTest("compiler/testData/codegen/box/reflection/mapping/openSuspendFun.kt");

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KDeclarationContainerImpl.kt

@@ -168,9 +168,16 @@ internal abstract class KDeclarationContainerImpl : ClassBasedDeclarationContain
     private fun Class<*>.lookupMethod(name: String, parameterTypes: List<Class<*>>, returnType: Class<*>, isPublic: Boolean): Method? {
         val parametersArray = parameterTypes.toTypedArray()
 
-        // If we're looking for a public method, just use Java reflection's getMethod/getMethods
+        // If we're looking for a public method, use Java reflection's getMethod/getMethods first
         if (isPublic) {
-            return tryGetMethod(name, parametersArray, returnType, declared = false)
+            val result = tryGetMethod(name, parametersArray, returnType, declared = false)
+            if (result != null) return result
+
+            // Methods from java.lang.Object cannot be found in the interface via Class.getMethod/getDeclaredMethod
+            if (isInterface) {
+                val fromObject = Any::class.java.lookupMethod(name, parameterTypes, returnType, isPublic)
+                if (fromObject != null) return fromObject
+            }
         }
 
         // If we're looking for a non-public method, it might be located not only in this class, but also in any of its superclasses