warning for access to private top-level declarations from another file

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -71,6 +71,7 @@ public interface Errors {
     DiagnosticFactory3<JetSimpleNameExpression, DeclarationDescriptor, Visibility, DeclarationDescriptor> INVISIBLE_REFERENCE =
             DiagnosticFactory3.create(ERROR);
     DiagnosticFactory3<PsiElement, DeclarationDescriptor, Visibility, DeclarationDescriptor> INVISIBLE_MEMBER = DiagnosticFactory3.create(ERROR, CALL_ELEMENT);
+    DiagnosticFactory3<PsiElement, DeclarationDescriptor, Visibility, JetFile> ACCESS_TO_PRIVATE_TOP_LEVEL_FROM_ANOTHER_FILE = DiagnosticFactory3.create(WARNING, CALL_ELEMENT);
 
     DiagnosticFactory1<JetElement, Collection<ClassDescriptor>> PLATFORM_CLASS_MAPPED_TO_KOTLIN = DiagnosticFactory1.create(WARNING);
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -624,6 +624,7 @@ public class DefaultErrorMessages {
         MAP.put(NON_LOCAL_RETURN_NOT_ALLOWED, "Can''t inline ''{0}'' here: it may contain non-local returns. Annotate parameter declaration ''{0}'' with ''inlineOptions(ONLY_LOCAL_RETURN)''", ELEMENT_TEXT, SHORT_NAMES_IN_TYPES, SHORT_NAMES_IN_TYPES);
         MAP.put(INLINE_CALL_CYCLE, "The ''{0}'' invocation is a part of inline cycle", NAME);
         MAP.put(NON_LOCAL_RETURN_IN_DISABLED_INLINE, "Non-local returns are not allowed with inlining disabled");
+        MAP.put(ACCESS_TO_PRIVATE_TOP_LEVEL_FROM_ANOTHER_FILE, "Access to private top-level declarations from another file will soon be forbidden: ''{0}'' is ''{1}'' in ''{2}''", NAME, TO_STRING, RENDER_FILE);
 
         MAP.setImmutable();
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/Renderers.kt

@@ -27,6 +27,7 @@ import org.jetbrains.kotlin.diagnostics.rendering.TabledDescriptorRenderer.newTa
 import org.jetbrains.kotlin.diagnostics.rendering.TabledDescriptorRenderer.newText
 import org.jetbrains.kotlin.psi.JetClass
 import org.jetbrains.kotlin.psi.JetClassOrObject
+import org.jetbrains.kotlin.psi.JetFile
 import org.jetbrains.kotlin.psi.JetNamedDeclaration
 import org.jetbrains.kotlin.renderer.DescriptorRenderer
 import org.jetbrains.kotlin.renderer.Renderer
@@ -87,6 +88,8 @@ public object Renderers {
 
     public val RENDER_TYPE: Renderer<JetType> = Renderer { DescriptorRenderer.FQ_NAMES_IN_TYPES.renderType(it) }
 
+    public val RENDER_FILE: Renderer<JetFile> = Renderer { it.name }
+
     public val RENDER_POSITION_VARIANCE: Renderer<Variance> = Renderer {
         variance: Variance ->
         when (variance) {

compiler/frontend/src/org/jetbrains/kotlin/resolve/TargetPlatform.kt

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.resolve
 import org.jetbrains.kotlin.container.StorageComponentContainer
 import org.jetbrains.kotlin.container.useInstance
 import org.jetbrains.kotlin.resolve.calls.checkers.*
+import org.jetbrains.kotlin.resolve.validation.AccessToPrivateTopLevelSymbolValidator
 import org.jetbrains.kotlin.resolve.validation.DeprecatedSymbolValidator
 import org.jetbrains.kotlin.resolve.validation.SymbolUsageValidator
 import org.jetbrains.kotlin.types.DynamicTypesSettings
@@ -40,7 +41,7 @@ public abstract class TargetPlatform(
 private val DEFAULT_DECLARATION_CHECKERS = listOf(DataClassAnnotationChecker())
 private val DEFAULT_CALL_CHECKERS = listOf(CapturingInClosureChecker(), InlineCheckerWrapper(), ReifiedTypeParameterSubstitutionChecker())
 private val DEFAULT_TYPE_CHECKERS = emptyList<AdditionalTypeChecker>()
-private val DEFAULT_VALIDATORS = listOf(DeprecatedSymbolValidator())
+private val DEFAULT_VALIDATORS = listOf(DeprecatedSymbolValidator(), AccessToPrivateTopLevelSymbolValidator())
 
 
 public open class PlatformConfigurator(

compiler/frontend/src/org/jetbrains/kotlin/resolve/validation/AccessToPrivateTopLevelSymbolValidator.kt

@@ -0,0 +1,66 @@
+/*
+ * 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.validation
+
+import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.psi.JetElement
+import org.jetbrains.kotlin.psi.JetFile
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.BindingTrace
+import org.jetbrains.kotlin.resolve.DescriptorToSourceUtils
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+
+public class AccessToPrivateTopLevelSymbolValidator : SymbolUsageValidator {
+    override fun validateCall(targetDescriptor: CallableDescriptor, trace: BindingTrace, element: PsiElement) {
+        val descriptor =
+            if (DescriptorUtils.isTopLevelDeclaration(targetDescriptor)) targetDescriptor
+            else DescriptorUtils.getContainingClass(targetDescriptor)
+
+        descriptor?.let {
+            reportIfNeeded(it, trace, element)
+        }
+    }
+
+    override fun validateTypeUsage(targetDescriptor: ClassifierDescriptor, trace: BindingTrace, element: PsiElement) =
+            reportIfNeeded(targetDescriptor, trace, element)
+
+    private fun reportIfNeeded(descriptor: DeclarationDescriptor, trace: BindingTrace, element: PsiElement) {
+        if (descriptor !is DeclarationDescriptorWithVisibility ||
+            descriptor.visibility != Visibilities.PRIVATE ||
+            !DescriptorUtils.isTopLevelDeclaration(descriptor)) return
+
+        if (descriptor is PropertySetterDescriptor && descriptor.correspondingProperty.visibility == Visibilities.PRIVATE) return
+
+        if (element !is JetElement) return
+
+        DescriptorToSourceUtils.getContainingFile(descriptor)?.let {
+            val jetFile = element.containingFile as? JetFile ?: return
+
+            val currentPackageViewDescriptor = trace.bindingContext.get(BindingContext.FILE_TO_PACKAGE_FRAGMENT, jetFile)
+            if (currentPackageViewDescriptor != null && !DescriptorUtils.areInSameModule(currentPackageViewDescriptor, descriptor)) return
+
+            val packageFqName = DescriptorUtils.getParentOfType(descriptor, PackageFragmentDescriptor::class.java)?.fqName
+            if (packageFqName != currentPackageViewDescriptor?.fqName) return
+
+            if (jetFile != it) {
+                trace.report(Errors.ACCESS_TO_PRIVATE_TOP_LEVEL_FROM_ANOTHER_FILE.on(element, descriptor, descriptor.visibility, it))
+            }
+        }
+    }
+}