Fix for KT-6383: Can't access a private static member of class object

#KT-6383 Fixed

compiler/backend/src/org/jetbrains/jet/codegen/PlatformStaticGenerator.kt

@@ -30,11 +30,10 @@ class PlatformStaticGenerator(
         val state: GenerationState
 ) : Function2<ImplementationBodyCodegen, ClassBuilder, Unit> {
 
-    override fun invoke(p1: ImplementationBodyCodegen, p2: ClassBuilder) {
+    override fun invoke(codegen: ImplementationBodyCodegen, classBuilder: ClassBuilder) {
         val typeMapper = state.getTypeMapper()
-        val callable = typeMapper.mapToCallableMethod(descriptor, false, p1.getContext())
-        val asmMethod = callable.getAsmMethod()
-        val methodVisitor = p2.newMethod(
+        val asmMethod = typeMapper.mapSignature(descriptor).getAsmMethod()
+        val methodVisitor = classBuilder.newMethod(
                 Synthetic(declarationOrigin.element, descriptor),
                 Opcodes.ACC_STATIC or AsmUtil.getMethodAsmFlags(descriptor, OwnerKind.IMPLEMENTATION),
                 asmMethod.getName()!!,
@@ -55,7 +54,13 @@ class PlatformStaticGenerator(
                 iv.load(index, paramType);
                 index += paramType.getSize();
             }
-            callable.invokeWithoutAssertions(iv)
+
+            val syntheticOrOriginalMethod = typeMapper.mapToCallableMethod(
+                    codegen.getContext().accessibleFunctionDescriptor(descriptor),
+                    false,
+                    codegen.getContext()
+            )
+            syntheticOrOriginalMethod.invokeWithoutAssertions(iv)
             iv.areturn(asmMethod.getReturnType());
             methodVisitor.visitEnd();
         }

compiler/testData/codegen/boxWithStdlib/platformStatic/syntheticAccessor.kt

@@ -0,0 +1,17 @@
+import kotlin.platform.*
+
+class C {
+    class object {
+        private platformStatic fun foo(): String {
+            return "OK"
+        }
+    }
+
+    fun bar(): String {
+        return foo()
+    }
+}
+
+fun box(): String {
+    return C().bar()
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxWithStdlibCodegenTestGenerated.java

@@ -1763,6 +1763,12 @@ public class BlackBoxWithStdlibCodegenTestGenerated extends AbstractBlackBoxCode
             String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/boxWithStdlib/platformStatic/simple.kt");
             doTestWithStdlib(fileName);
         }
+
+        @TestMetadata("syntheticAccessor.kt")
+        public void testSyntheticAccessor() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/boxWithStdlib/platformStatic/syntheticAccessor.kt");
+            doTestWithStdlib(fileName);
+        }
     }
 
     @TestMetadata("compiler/testData/codegen/boxWithStdlib/platformTypes")