Calls to non-@JvmStatic protected members of companion objects from subclasses are now errors (unsupported yet)

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/ProtectedInSuperClassCompanionCallChecker.kt

@@ -0,0 +1,51 @@
+/*
+ * 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.resolve.jvm.checkers
+
+import org.jetbrains.kotlin.descriptors.CallableDescriptor
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.Visibilities
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+import org.jetbrains.kotlin.resolve.annotations.hasJvmStaticAnnotation
+import org.jetbrains.kotlin.resolve.calls.checkers.CallChecker
+import org.jetbrains.kotlin.resolve.calls.context.BasicCallResolutionContext
+import org.jetbrains.kotlin.resolve.calls.model.ResolvedCall
+import org.jetbrains.kotlin.resolve.descriptorUtil.parentsWithSelf
+import org.jetbrains.kotlin.resolve.jvm.diagnostics.ErrorsJvm
+
+class ProtectedInSuperClassCompanionCallChecker : CallChecker {
+
+    override fun <F : CallableDescriptor> check(resolvedCall: ResolvedCall<F>, context: BasicCallResolutionContext) {
+        val targetDescriptor = resolvedCall.resultingDescriptor.original
+        // Protected non-JVM static
+        if (targetDescriptor.visibility != Visibilities.PROTECTED) return
+        if (targetDescriptor.hasJvmStaticAnnotation()) return
+        val containerDescriptor = targetDescriptor.containingDeclaration
+        // Declared in companion object
+        if (containerDescriptor is ClassDescriptor && containerDescriptor.isCompanionObject) {
+            val companionDescriptor = containerDescriptor
+            val companionOwnerDescriptor = companionDescriptor.containingDeclaration as? ClassDescriptor ?: return
+            val parentClassDescriptors = context.scope.ownerDescriptor.parentsWithSelf.filterIsInstance<ClassDescriptor>()
+            // Called from within a derived class
+            if (!parentClassDescriptors.any { DescriptorUtils.isSubclass(it, companionOwnerDescriptor) }) return
+            // Called not within the same companion object or its owner class
+            if (companionDescriptor !in parentClassDescriptors && companionOwnerDescriptor !in parentClassDescriptors) {
+                context.trace.report(ErrorsJvm.SUBCLASS_CANT_CALL_COMPANION_PROTECTED_NON_STATIC.on(resolvedCall.call.callElement));
+            }
+        }
+    }
+}

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/DefaultErrorMessagesJvm.java

@@ -81,6 +81,7 @@ public class DefaultErrorMessagesJvm implements DefaultErrorMessages.Extension {
                 "Expected type does not accept nulls in {0}, but the value may be null in {1}", Renderers.TO_STRING, Renderers.TO_STRING);
 
         MAP.put(ErrorsJvm.INTERFACE_CANT_CALL_DEFAULT_METHOD_VIA_SUPER, "Interfaces can't call Java default methods via super");
+        MAP.put(ErrorsJvm.SUBCLASS_CANT_CALL_COMPANION_PROTECTED_NON_STATIC, "Using non-JVM static members protected in the superclass companion is unsupported yet");
 
         MAP.put(ErrorsJvm.WHEN_ENUM_CAN_BE_NULL_IN_JAVA, "Enum argument can be null in Java, but exhaustive when contains no null branch");
 

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/ErrorsJvm.java

@@ -68,6 +68,7 @@ public interface ErrorsJvm {
     DiagnosticFactory1<KtAnnotationEntry, FqName> ANNOTATION_IS_NOT_APPLICABLE_TO_MULTIFILE_CLASSES = DiagnosticFactory1.create(ERROR);
 
     DiagnosticFactory0<KtElement> INTERFACE_CANT_CALL_DEFAULT_METHOD_VIA_SUPER = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<KtElement> SUBCLASS_CANT_CALL_COMPANION_PROTECTED_NON_STATIC = DiagnosticFactory0.create(ERROR);
 
     DiagnosticFactory0<KtElement> NO_REFLECTION_IN_CLASS_PATH = DiagnosticFactory0.create(WARNING);
 

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/platform/JvmPlatformConfigurator.kt

@@ -46,7 +46,8 @@ public object JvmPlatformConfigurator : PlatformConfigurator(
                 NeedSyntheticChecker(),
                 JavaAnnotationCallChecker(),
                 TraitDefaultMethodCallChecker(),
-                JavaClassOnCompanionChecker()
+                JavaClassOnCompanionChecker(),
+                ProtectedInSuperClassCompanionCallChecker()
         ),
 
         additionalTypeCheckers = listOf(