Synthesized 'copy' in data classes cannot override anything since 1.3

Synthesized 'copy' introduces default values for parameters, which is
prohibited for regular overrides.
Report warning in language version 1.2-, error in 1.3+.

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

@@ -394,6 +394,10 @@ public interface Errors {
 
     DiagnosticFactory2<PsiElement, CallableMemberDescriptor, DeclarationDescriptor> DATA_CLASS_OVERRIDE_CONFLICT =
             DiagnosticFactory2.create(ERROR);
+    DiagnosticFactory2<PsiElement, CallableMemberDescriptor, DeclarationDescriptor> DATA_CLASS_OVERRIDE_DEFAULT_VALUES_WARNING =
+            DiagnosticFactory2.create(WARNING);
+    DiagnosticFactory2<PsiElement, CallableMemberDescriptor, DeclarationDescriptor> DATA_CLASS_OVERRIDE_DEFAULT_VALUES_ERROR =
+            DiagnosticFactory2.create(ERROR);
 
     DiagnosticFactory1<KtDeclaration, CallableMemberDescriptor> CANNOT_INFER_VISIBILITY =
             DiagnosticFactory1.create(ERROR, DECLARATION_SIGNATURE_OR_DEFAULT);

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

@@ -290,6 +290,8 @@ public class DefaultErrorMessages {
         MAP.put(VIRTUAL_MEMBER_HIDDEN, "''{0}'' hides member of supertype ''{2}'' and needs ''override'' modifier", NAME, NAME, NAME);
 
         MAP.put(DATA_CLASS_OVERRIDE_CONFLICT, "Function ''{0}'' generated for the data class conflicts with member of supertype ''{1}''", NAME, NAME);
+        MAP.put(DATA_CLASS_OVERRIDE_DEFAULT_VALUES_WARNING, "Function ''{0}'' generated for the data class has default values for parameters, and conflicts with member of supertype ''{1}''", NAME, NAME);
+        MAP.put(DATA_CLASS_OVERRIDE_DEFAULT_VALUES_ERROR, "Function ''{0}'' generated for the data class has default values for parameters, and conflicts with member of supertype ''{1}''", NAME, NAME);
 
         MAP.put(CANNOT_OVERRIDE_INVISIBLE_MEMBER, "''{0}'' has no access to ''{1}'', so it cannot override it", FQ_NAMES_IN_TYPES,
                 FQ_NAMES_IN_TYPES);

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

@@ -22,6 +22,8 @@ import com.intellij.psi.PsiElement
 import com.intellij.util.SmartList
 import com.intellij.util.containers.ContainerUtil
 import com.intellij.util.containers.SmartHashSet
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.config.LanguageVersionSettings
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor.Kind.DELEGATION
 import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor.Kind.FAKE_OVERRIDE
@@ -41,7 +43,8 @@ import java.util.*
 
 class OverrideResolver(
         private val trace: BindingTrace,
-        private val overridesBackwardCompatibilityHelper: OverridesBackwardCompatibilityHelper
+        private val overridesBackwardCompatibilityHelper: OverridesBackwardCompatibilityHelper,
+        private val languageVersionSettings: LanguageVersionSettings
 ) {
 
     fun check(c: TopDownAnalysisContext) {
@@ -244,6 +247,9 @@ class OverrideResolver(
             if (DataClassDescriptorResolver.isComponentLike(declared.name)) {
                 checkOverrideForComponentFunction(declared)
             }
+            else if (declared.name == DataClassDescriptorResolver.COPY_METHOD_NAME) {
+                checkOverrideForCopyFunction(declared)
+            }
             return
         }
 
@@ -341,6 +347,20 @@ class OverrideResolver(
         })
     }
 
+    private fun checkOverrideForCopyFunction(copyFunction: CallableMemberDescriptor) {
+        val overridden = copyFunction.overriddenDescriptors.firstOrNull()
+        if (overridden != null) {
+            val baseClassifier = overridden.containingDeclaration
+            val dataModifier = findDataModifierForDataClass(copyFunction.containingDeclaration)
+            if (languageVersionSettings.supportsFeature(LanguageFeature.ProhibitDataClassesOverridingCopy)) {
+                trace.report(DATA_CLASS_OVERRIDE_DEFAULT_VALUES_ERROR.on(dataModifier, copyFunction, baseClassifier))
+            }
+            else {
+                trace.report(DATA_CLASS_OVERRIDE_DEFAULT_VALUES_WARNING.on(dataModifier, copyFunction, baseClassifier))
+            }
+        }
+    }
+
     private fun checkParameterOverridesForAllClasses(c: TopDownAnalysisContext) {
         for (classDescriptor in c.declaredClasses.values) {
             for (member in DescriptorUtils.getAllDescriptors(classDescriptor.defaultType.memberScope)) {