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)) {

compiler/testData/codegen/box/dataClasses/copy/kt12708.kt

@@ -1,3 +1,5 @@
+// LANGUAGE_VERSION: 1.1
+
 fun box(): String {
     val a: A = B(1)
     a.copy(1)

compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyNoDefaults.kt

@@ -0,0 +1,9 @@
+// !LANGUAGE: +ProhibitDataClassesOverridingCopy
+
+interface WithCopy<T> {
+    fun copy(str: T): WithCopy<T>
+}
+
+<!DATA_CLASS_OVERRIDE_DEFAULT_VALUES_ERROR!>data<!> class <!CONFLICTING_JVM_DECLARATIONS, CONFLICTING_JVM_DECLARATIONS!>Test(val str: String)<!> : WithCopy<String> {
+    <!CONFLICTING_OVERLOADS!>override fun copy(str: String)<!> = Test(str)
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyNoDefaults.txt

@@ -0,0 +1,19 @@
+package
+
+public final data class Test : WithCopy<kotlin.String> {
+    public constructor Test(/*0*/ str: kotlin.String)
+    public final val str: kotlin.String
+    public final operator /*synthesized*/ fun component1(): kotlin.String
+    public open override /*1*/ fun copy(/*0*/ str: kotlin.String): Test
+    public final override /*1*/ /*synthesized*/ fun copy(/*0*/ str: kotlin.String = ...): Test
+    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
+}
+
+public interface WithCopy</*0*/ T> {
+    public abstract fun copy(/*0*/ str: T): WithCopy<T>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyWithDefaults.kt

@@ -0,0 +1,9 @@
+// !LANGUAGE: +ProhibitDataClassesOverridingCopy
+
+interface WithCopy<T> {
+    fun copy(str: T): WithCopy<T>
+}
+
+<!DATA_CLASS_OVERRIDE_DEFAULT_VALUES_ERROR!>data<!> class <!CONFLICTING_JVM_DECLARATIONS, CONFLICTING_JVM_DECLARATIONS, CONFLICTING_JVM_DECLARATIONS!>Test(val str: String)<!> : WithCopy<String> {
+    <!CONFLICTING_OVERLOADS!>override fun copy(str: String = <!DEFAULT_VALUE_NOT_ALLOWED_IN_OVERRIDE!>this.str<!>)<!> = Test(str)
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyWithDefaults.txt

@@ -0,0 +1,19 @@
+package
+
+public final data class Test : WithCopy<kotlin.String> {
+    public constructor Test(/*0*/ str: kotlin.String)
+    public final val str: kotlin.String
+    public final operator /*synthesized*/ fun component1(): kotlin.String
+    public open override /*1*/ fun copy(/*0*/ str: kotlin.String = ...): Test
+    public final override /*1*/ /*synthesized*/ fun copy(/*0*/ str: kotlin.String = ...): Test
+    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
+}
+
+public interface WithCopy</*0*/ T> {
+    public abstract fun copy(/*0*/ str: T): WithCopy<T>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassNotOverridingCopy.kt

@@ -0,0 +1,9 @@
+// !LANGUAGE: +ProhibitDataClassesOverridingCopy
+
+interface WithCopy<T> {
+    fun copy(str: T): WithCopy<T>
+}
+
+data class Test(val str: String, val int: Int) : WithCopy<String> {
+    override fun copy(str: String) = copy(str, int)
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassNotOverridingCopy.txt

@@ -0,0 +1,21 @@
+package
+
+public final data class Test : WithCopy<kotlin.String> {
+    public constructor Test(/*0*/ str: kotlin.String, /*1*/ int: kotlin.Int)
+    public final val int: kotlin.Int
+    public final val str: kotlin.String
+    public final operator /*synthesized*/ fun component1(): kotlin.String
+    public final operator /*synthesized*/ fun component2(): kotlin.Int
+    public open override /*1*/ fun copy(/*0*/ str: kotlin.String): Test
+    public final /*synthesized*/ fun copy(/*0*/ str: kotlin.String = ..., /*1*/ int: kotlin.Int = ...): Test
+    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
+}
+
+public interface WithCopy</*0*/ T> {
+    public abstract fun copy(/*0*/ str: T): WithCopy<T>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv12.kt

@@ -0,0 +1,7 @@
+// !LANGUAGE: -ProhibitDataClassesOverridingCopy
+
+interface WithCopy<T> {
+    fun copy(str: T): WithCopy<T>
+}
+
+<!DATA_CLASS_OVERRIDE_DEFAULT_VALUES_WARNING!>data<!> class Test(val str: String): WithCopy<String>

compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv12.txt

@@ -0,0 +1,18 @@
+package
+
+public final data class Test : WithCopy<kotlin.String> {
+    public constructor Test(/*0*/ str: kotlin.String)
+    public final val str: kotlin.String
+    public final operator /*synthesized*/ fun component1(): kotlin.String
+    public final override /*1*/ /*synthesized*/ fun copy(/*0*/ str: kotlin.String = ...): Test
+    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
+}
+
+public interface WithCopy</*0*/ T> {
+    public abstract fun copy(/*0*/ str: T): WithCopy<T>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv13.kt

@@ -0,0 +1,7 @@
+// !LANGUAGE: +ProhibitDataClassesOverridingCopy
+
+interface WithCopy<T> {
+    fun copy(str: T): WithCopy<T>
+}
+
+<!DATA_CLASS_OVERRIDE_DEFAULT_VALUES_ERROR!>data<!> class Test(val str: String): WithCopy<String>

compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv13.txt

@@ -0,0 +1,18 @@
+package
+
+public final data class Test : WithCopy<kotlin.String> {
+    public constructor Test(/*0*/ str: kotlin.String)
+    public final val str: kotlin.String
+    public final operator /*synthesized*/ fun component1(): kotlin.String
+    public final override /*1*/ /*synthesized*/ fun copy(/*0*/ str: kotlin.String = ...): Test
+    public open override /*1*/ /*synthesized*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*synthesized*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*synthesized*/ fun toString(): kotlin.String
+}
+
+public interface WithCopy</*0*/ T> {
+    public abstract fun copy(/*0*/ str: T): WithCopy<T>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -4828,12 +4828,42 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("dataClassExplicitlyOverridingCopyNoDefaults.kt")
+            public void testDataClassExplicitlyOverridingCopyNoDefaults() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyNoDefaults.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("dataClassExplicitlyOverridingCopyWithDefaults.kt")
+            public void testDataClassExplicitlyOverridingCopyWithDefaults() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyWithDefaults.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("dataClassNoName.kt")
             public void testDataClassNoName() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassNoName.kt");
                 doTest(fileName);
             }
 
+            @TestMetadata("dataClassNotOverridingCopy.kt")
+            public void testDataClassNotOverridingCopy() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassNotOverridingCopy.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("dataClassOverridingCopy_lv12.kt")
+            public void testDataClassOverridingCopy_lv12() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv12.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("dataClassOverridingCopy_lv13.kt")
+            public void testDataClassOverridingCopy_lv13() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv13.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("dataClassVarargParam.kt")
             public void testDataClassVarargParam() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassVarargParam.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -4828,12 +4828,42 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 doTest(fileName);
             }
 
+            @TestMetadata("dataClassExplicitlyOverridingCopyNoDefaults.kt")
+            public void testDataClassExplicitlyOverridingCopyNoDefaults() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyNoDefaults.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("dataClassExplicitlyOverridingCopyWithDefaults.kt")
+            public void testDataClassExplicitlyOverridingCopyWithDefaults() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassExplicitlyOverridingCopyWithDefaults.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("dataClassNoName.kt")
             public void testDataClassNoName() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassNoName.kt");
                 doTest(fileName);
             }
 
+            @TestMetadata("dataClassNotOverridingCopy.kt")
+            public void testDataClassNotOverridingCopy() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassNotOverridingCopy.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("dataClassOverridingCopy_lv12.kt")
+            public void testDataClassOverridingCopy_lv12() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv12.kt");
+                doTest(fileName);
+            }
+
+            @TestMetadata("dataClassOverridingCopy_lv13.kt")
+            public void testDataClassOverridingCopy_lv13() throws Exception {
+                String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassOverridingCopy_lv13.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("dataClassVarargParam.kt")
             public void testDataClassVarargParam() throws Exception {
                 String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassVarargParam.kt");

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -65,6 +65,7 @@ enum class LanguageFeature(
 
     RestrictionOfValReassignmentViaBackingField(KOTLIN_1_3),
     NestedClassesInEnumEntryShouldBeInner(KOTLIN_1_3),
+    ProhibitDataClassesOverridingCopy(KOTLIN_1_3),
     RestrictionOfWrongAnnotationsWithUseSiteTargetsOnTypes(KOTLIN_1_3),
 
     // Experimental features