KT-11645 generate backing field for 'private const val' in part implementation class

compiler/backend/src/org/jetbrains/kotlin/codegen/PropertyCodegen.java

@@ -142,9 +142,10 @@ public class PropertyCodegen {
 
         Annotations propertyAnnotations = annotationSplitter.getAnnotationsForTarget(AnnotationUseSiteTarget.PROPERTY);
 
-        // Fields and '$annotations' methods for const properties are generated in the multi-file facade
-        boolean isBackingFieldOwner =
-                descriptor.isConst() ? !(context instanceof MultifileClassPartContext) : CodegenContextUtil.isImplClassOwner(context);
+        // Fields and '$annotations' methods for non-private const properties are generated in the multi-file facade
+        boolean isBackingFieldOwner = descriptor.isConst() && !Visibilities.isPrivate(descriptor.getVisibility())
+                                      ? !(context instanceof MultifileClassPartContext)
+                                      : CodegenContextUtil.isImplClassOwner(context);
 
         if (isBackingFieldOwner) {
             Annotations fieldAnnotations = annotationSplitter.getAnnotationsForTarget(AnnotationUseSiteTarget.FIELD);

compiler/testData/codegen/box/multifileClasses/privateConstVal.kt

@@ -0,0 +1,23 @@
+// WITH_RUNTIME
+// FILE: foo.kt
+@file:JvmName("Util")
+@file:JvmMultifileClass
+package test
+
+private const val x = "O"
+
+fun foo() = x
+
+// FILE: bar.kt
+@file:JvmName("Util")
+@file:JvmMultifileClass
+package test
+
+private const val x = "K"
+
+fun bar() = x
+
+// FILE: test.kt
+package test
+
+fun box(): String = foo() + bar()

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

@@ -8482,6 +8482,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             doTest(fileName);
         }
 
+        @TestMetadata("privateConstVal.kt")
+        public void testPrivateConstVal() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/multifileClasses/privateConstVal.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("samePartNameDifferentFacades.kt")
         public void testSamePartNameDifferentFacades() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/multifileClasses/samePartNameDifferentFacades.kt");