Fix light class exception on empty multifile facade

Fix generating multifile facade with all members private (in bytecode)
leading to delegate not being generated for corresponding light class

 #KT-20966 Fixed

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

@@ -1,47 +0,0 @@
-/*
- * Copyright 2010-2015 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.codegen;
-
-import kotlin.jvm.functions.Function0;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.kotlin.storage.LockBasedStorageManager;
-import org.jetbrains.kotlin.storage.NotNullLazyValue;
-
-public class ClassBuilderOnDemand extends DelegatingClassBuilder {
-    private final NotNullLazyValue<ClassBuilder> classBuilder;
-
-    public ClassBuilderOnDemand(@NotNull Function0<ClassBuilder> createClassBuilder) {
-        this.classBuilder = LockBasedStorageManager.NO_LOCKS.createLazyValue(createClassBuilder);
-    }
-
-    @Override
-    @NotNull
-    protected ClassBuilder getDelegate() {
-        return classBuilder.invoke();
-    }
-
-    @Override
-    public void done() {
-        if (isComputed()) {
-            classBuilder.invoke().done();
-        }
-    }
-
-    public boolean isComputed() {
-        return classBuilder.isComputed();
-    }
-}

compiler/backend/src/org/jetbrains/kotlin/codegen/ClassBuilderOnDemand.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.codegen
+
+import org.jetbrains.kotlin.storage.LockBasedStorageManager
+
+class ClassBuilderOnDemand(createClassBuilder: () -> ClassBuilder) : DelegatingClassBuilder() {
+    private val classBuilder = LockBasedStorageManager.NO_LOCKS.createLazyValue(createClassBuilder)
+
+    val isComputed: Boolean
+        get() = classBuilder.isComputed()
+
+    override fun getDelegate() = classBuilder()
+
+    fun ensureGenerated() {
+        classBuilder()
+    }
+
+    override fun done() {
+        if (isComputed) {
+            classBuilder().done()
+        }
+    }
+}

compiler/backend/src/org/jetbrains/kotlin/codegen/MultifileClassCodegen.kt

@@ -317,7 +317,10 @@ class MultifileClassCodegenImpl(
     }
 
     private fun writeKotlinMultifileFacadeAnnotationIfNeeded() {
-        if (!state.classBuilderMode.generateMetadata) return
+        if (!state.classBuilderMode.generateMetadata) {
+            classBuilder.ensureGenerated()
+            return
+        }
         if (files.any { it.isScript() }) return
 
         val extraFlags = if (shouldGeneratePartHierarchy) JvmAnnotationNames.METADATA_MULTIFILE_PARTS_INHERIT_FLAG else 0