JVM IR: Fix compilation of inline functions in anonymous objects...

...in class members. The corresponding classes end up nested in the
class initializer of the surrounding class and we need to take this into
account when creating instances of ClassCodegen.

This fixes KT-40332 on the JVM IR backend.

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ClassCodegen.kt

@@ -226,7 +226,16 @@ abstract class ClassCodegen protected constructor(
         fun getOrCreate(
             irClass: IrClass,
             context: JvmBackendContext,
-            parentFunction: IrFunction? = null,
+            // The `parentFunction` is only set for classes nested inside of functions. This is usually safe, since there is no
+            // way to refer to (inline) members of such a class from outside of the function unless the function in question is
+            // itself declared as inline. In that case, the function will be compiled before we can refer to the nested class.
+            //
+            // The one exception to this rule are anonymous objects defined as members of a class. These are nested inside of the
+            // class initializer, but can be referred to from anywhere within the scope of the class. That's why we have to ensure
+            // that all references to classes inside of <clinit> have a non-null `parentFunction`.
+            parentFunction: IrFunction? = irClass.parent.safeAs<IrFunction>()?.takeIf {
+                it.origin == JvmLoweredDeclarationOrigin.CLASS_STATIC_INITIALIZER
+            },
         ): ClassCodegen =
             context.classCodegens.getOrPut(irClass) {
                 context.createCodegen(irClass, context, parentFunction) ?: DescriptorBasedClassCodegen(irClass, context, parentFunction)