[EE-IR] Add "different classloader" check to synthetic accessor lowering

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/ReflectiveAccess.kt

@@ -74,7 +74,7 @@ internal class ReflectiveAccessLowering(
 
     // Wrapper for the logic from SyntheticAccessorLowering
     private fun IrSymbol.isAccessible(withSuper: Boolean = false): Boolean {
-        return isAccessible(context, currentScope, inlineScopeResolver, withSuper, null)
+        return isAccessible(context, currentScope, inlineScopeResolver, withSuper, null, fromOtherClassLoader = true)
     }
 
     // Fragments are transformed in a post-order traversal: children first,

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/SyntheticAccessorLowering.kt

@@ -55,6 +55,7 @@ internal class SyntheticAccessorLowering(val context: JvmBackendContext) : FileL
             currentScope: ScopeWithIr?,
             inlineScopeResolver: IrInlineScopeResolver,
             withSuper: Boolean, thisObjReference: IrClassSymbol?,
+            fromOtherClassLoader: Boolean = false
         ): Boolean {
             /// We assume that IR code that reaches us has been checked for correctness at the frontend.
             /// This function needs to single out those cases where Java accessibility rules differ from Kotlin's.
@@ -92,8 +93,9 @@ internal class SyntheticAccessorLowering(val context: JvmBackendContext) : FileL
             return when {
                 jvmVisibility == 0 /* package only */ -> samePackage
                 jvmVisibility == Opcodes.ACC_PRIVATE -> ownerClass == scopeClassOrPackage
-                // JVM `protected`, unlike Kotlin `protected`, permits accesses from the same package.
-                !withSuper && samePackage -> true
+                // JVM `protected`, unlike Kotlin `protected`, permits accesses from the same package,
+                // provided the call is not across class loader boundaries.
+                !withSuper && samePackage && !fromOtherClassLoader -> true
                 // Super calls and cross-package protected accesses are both only possible from a subclass of the declaration
                 // owner. Also, the target of a non-static call must be assignable to the current class. This is a verification
                 // constraint: https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.10.1.8