Deprecations: data class should now have at least one primary constructor parameter, parameters should be val / var and not vararg.

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

@@ -382,6 +382,10 @@ public interface Errors {
     DiagnosticFactory2<JetClassOrObject, Collection<? extends CallableMemberDescriptor>, Integer> DIFFERENT_NAMES_FOR_THE_SAME_PARAMETER_IN_SUPERTYPES =
             DiagnosticFactory2.create(WARNING, DECLARATION_NAME);
 
+    DiagnosticFactory0<PsiElement> DATA_CLASS_WITHOUT_PARAMETERS = DiagnosticFactory0.create(WARNING);
+    DiagnosticFactory0<JetParameter> DATA_CLASS_VARARG_PARAMETER = DiagnosticFactory0.create(WARNING);
+    DiagnosticFactory0<JetParameter> DATA_CLASS_NOT_PROPERTY_PARAMETER = DiagnosticFactory0.create(WARNING);
+
     ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
     // Errors/warnings inside code blocks

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

@@ -622,6 +622,10 @@ public class DefaultErrorMessages {
                     "Names of the parameter #{1} conflict in the following members of supertypes: ''{0}''. " +
                     "This may cause problems when calling this function with named arguments.", commaSeparated(FQ_NAMES_IN_TYPES), TO_STRING);
 
+        MAP.put(DATA_CLASS_WITHOUT_PARAMETERS, "Data class without primary constructor parameters are deprecated");
+        MAP.put(DATA_CLASS_VARARG_PARAMETER, "Primary constructor vararg parameters are deprecated for data classes");
+        MAP.put(DATA_CLASS_NOT_PROPERTY_PARAMETER, "Primary constructor parameters without val / var are deprecated for data classes");
+
         MAP.put(AMBIGUOUS_ANONYMOUS_TYPE_INFERRED, "Right-hand side has anonymous type. Please specify type explicitly", TO_STRING);
 
         MAP.put(EXTENSION_IN_CLASS_REFERENCE_NOT_ALLOWED,

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

@@ -36,6 +36,19 @@ public class DataClassAnnotationChecker : DeclarationChecker {
             if (descriptor.getUnsubstitutedPrimaryConstructor() == null && descriptor.getConstructors().isNotEmpty()) {
                 diagnosticHolder.report(Errors.PRIMARY_CONSTRUCTOR_REQUIRED_FOR_DATA_CLASS.on(declaration.getNameIdentifier()));
             }
+            val primaryConstructor = declaration.getPrimaryConstructor()
+            val parameters = primaryConstructor?.valueParameters ?: emptyList()
+            if (parameters.isEmpty()) {
+                diagnosticHolder.report(Errors.DATA_CLASS_WITHOUT_PARAMETERS.on(declaration.nameIdentifier!!))
+            }
+            for (parameter in parameters) {
+                if (parameter.isVarArg) {
+                    diagnosticHolder.report(Errors.DATA_CLASS_VARARG_PARAMETER.on(parameter))
+                }
+                if (!parameter.hasValOrVar()) {
+                    diagnosticHolder.report(Errors.DATA_CLASS_NOT_PROPERTY_PARAMETER.on(parameter))
+                }
+            }
         }
     }
 }

compiler/testData/diagnostics/tests/annotations/options/target.kt

@@ -1,5 +1,4 @@
 @Target(AnnotationTarget.CLASS)
 annotation class base
 
-@base data class My
+@base data class My(val x: Int)
-

compiler/testData/diagnostics/tests/annotations/options/target.txt

@@ -1,8 +1,10 @@
 package
 
 @base() @kotlin.data() public final class My {
-    public constructor My()
+    public constructor My(/*0*/ x: kotlin.Int)
-    public final /*synthesized*/ fun copy(): My
+    public final val x: kotlin.Int
+    public final /*synthesized*/ fun component1(): kotlin.Int
+    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int = ...): My
     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/bothParamsAreNotProperties.kt

@@ -1,6 +0,0 @@
-data class A(<!UNUSED_PARAMETER!>x<!>: Int, <!UNUSED_PARAMETER!>y<!>: String)
-
-fun foo(a: A) {
-    a.<!UNRESOLVED_REFERENCE!>component1<!>()
-    a.<!UNRESOLVED_REFERENCE!>component2<!>()
-}

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

@@ -1,11 +0,0 @@
-package
-
-public fun foo(/*0*/ a: A): kotlin.Unit
-
-@kotlin.data() public final class A {
-    public constructor A(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String)
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String): A
-    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/dataClassVarargParam.kt

@@ -0,0 +1,3 @@
+data class My(val x: Int, <!DATA_CLASS_VARARG_PARAMETER!>vararg val y: String<!>)
+
+data class Your(<!DATA_CLASS_VARARG_PARAMETER, DATA_CLASS_NOT_PROPERTY_PARAMETER!>vararg <!UNUSED_PARAMETER!>z<!>: String<!>)

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

@@ -0,0 +1,21 @@
+package
+
+@kotlin.data() public final class My {
+    public constructor My(/*0*/ x: kotlin.Int, /*1*/ vararg y: kotlin.String /*kotlin.Array<out kotlin.String>*/)
+    public final val x: kotlin.Int
+    public final val y: kotlin.Array<out kotlin.String>
+    public final /*synthesized*/ fun component1(): kotlin.Int
+    public final /*synthesized*/ fun component2(): kotlin.Array<out kotlin.String>
+    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int = ..., /*1*/ vararg y: kotlin.String /*kotlin.Array<out kotlin.String>*/ = ...): My
+    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
+}
+
+@kotlin.data() public final class Your {
+    public constructor Your(/*0*/ vararg z: kotlin.String /*kotlin.Array<out kotlin.String>*/)
+    public final /*synthesized*/ fun copy(/*0*/ vararg z: kotlin.String /*kotlin.Array<out kotlin.String>*/): Your
+    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/dataInheritance.kt

@@ -6,6 +6,6 @@ open class NotAllowed
 
 class Derived: Base(42)
 
-<!DATA_CLASS_OVERRIDE_CONFLICT!>data<!> class Nasty(x: Int, val y: Int): <!DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES!>Base<!>(x)
+<!DATA_CLASS_OVERRIDE_CONFLICT!>data<!> class Nasty(val z: Int, val y: Int): <!DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES!>Base<!>(z)
 
 data class Complex(val y: Int): Allowed, <!DATA_CLASS_CANNOT_HAVE_CLASS_SUPERTYPES!>NotAllowed<!>()

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

@@ -37,12 +37,14 @@ public final class Derived : Base {
 }
 
 @kotlin.data() public final class Nasty : Base {
-    public constructor Nasty(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.Int)
+    public constructor Nasty(/*0*/ z: kotlin.Int, /*1*/ y: kotlin.Int)
     public final override /*1*/ /*fake_override*/ val x: kotlin.Int
     public final val y: kotlin.Int
+    public final val z: kotlin.Int
     public final override /*1*/ /*synthesized*/ fun component1(): kotlin.Int
+    public final /*synthesized*/ fun component2(): kotlin.Int
     public final override /*1*/ /*fake_override*/ fun copy(/*0*/ x: kotlin.Int = ...): Base
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.Int = ...): Nasty
+    public final /*synthesized*/ fun copy(/*0*/ z: kotlin.Int = ..., /*1*/ y: kotlin.Int = ...): Nasty
     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/emptyConstructor.kt

@@ -1,4 +1,4 @@
-data class A()
+data class <!DATA_CLASS_WITHOUT_PARAMETERS!>A<!>()
 
 fun foo(a: A) {
     a.<!UNRESOLVED_REFERENCE!>component1<!>()

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

@@ -1,8 +0,0 @@
-// !CHECK_TYPE
-
-data class A(val x: Int, <!UNUSED_PARAMETER!>y<!>: String)
-
-fun foo(a: A) {
-    checkSubtype<Int>(a.component1())
-    a.<!UNRESOLVED_REFERENCE!>component2<!>()
-}

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

@@ -1,13 +0,0 @@
-package
-
-public fun foo(/*0*/ a: A): kotlin.Unit
-
-@kotlin.data() public final class A {
-    public constructor A(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String)
-    public final val x: kotlin.Int
-    public final /*synthesized*/ fun component1(): kotlin.Int
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int = ..., /*1*/ y: kotlin.String): A
-    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/firstParamIsVar.kt

@@ -1,8 +0,0 @@
-// !CHECK_TYPE
-
-data class A(var x: Int, <!UNUSED_PARAMETER!>y<!>: String)
-
-fun foo(a: A) {
-    checkSubtype<Int>(a.component1())
-    a.<!UNRESOLVED_REFERENCE!>component2<!>()
-}

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

@@ -1,13 +0,0 @@
-package
-
-public fun foo(/*0*/ a: A): kotlin.Unit
-
-@kotlin.data() public final class A {
-    public constructor A(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String)
-    public final var x: kotlin.Int
-    public final /*synthesized*/ fun component1(): kotlin.Int
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int = ..., /*1*/ y: kotlin.String): A
-    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/noConstructor.kt

@@ -1,4 +1,4 @@
-data class A
+data class <!DATA_CLASS_WITHOUT_PARAMETERS!>A<!>
 
 fun foo(a: A) {
     a.<!UNRESOLVED_REFERENCE!>component1<!>()

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

@@ -1,10 +0,0 @@
-data class A(foo: String, val bar: Int, other: Long) {
-    val foo = foo
-    val other = other
-}
-
-fun test(a: A) {
-    a.component1()
-    a.<!UNRESOLVED_REFERENCE!>component2<!>()
-    a.<!UNRESOLVED_REFERENCE!>component3<!>()
-}

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

@@ -1,15 +0,0 @@
-package
-
-public fun test(/*0*/ a: A): kotlin.Unit
-
-@kotlin.data() public final class A {
-    public constructor A(/*0*/ foo: kotlin.String, /*1*/ bar: kotlin.Int, /*2*/ other: kotlin.Long)
-    public final val bar: kotlin.Int
-    public final val foo: kotlin.String
-    public final val other: kotlin.Long
-    public final /*synthesized*/ fun component1(): kotlin.Int
-    public final /*synthesized*/ fun copy(/*0*/ foo: kotlin.String, /*1*/ bar: kotlin.Int = ..., /*2*/ other: kotlin.Long): A
-    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/secondParamIsVal.kt

@@ -1,8 +0,0 @@
-// !CHECK_TYPE
-
-data class A(<!UNUSED_PARAMETER!>x<!>: Int, val y: String)
-
-fun foo(a: A) {
-    checkSubtype<String>(a.component1())
-    a.<!UNRESOLVED_REFERENCE!>component2<!>()
-}

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

@@ -1,13 +0,0 @@
-package
-
-public fun foo(/*0*/ a: A): kotlin.Unit
-
-@kotlin.data() public final class A {
-    public constructor A(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String)
-    public final val y: kotlin.String
-    public final /*synthesized*/ fun component1(): kotlin.String
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String = ...): A
-    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/secondParamIsVar.kt

@@ -1,8 +0,0 @@
-// !CHECK_TYPE
-
-data class A(<!UNUSED_PARAMETER!>x<!>: Int, var y: String)
-
-fun foo(a: A) {
-    checkSubtype<String>(a.component1())
-    a.<!UNRESOLVED_REFERENCE!>component2<!>()
-}

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

@@ -1,13 +0,0 @@
-package
-
-public fun foo(/*0*/ a: A): kotlin.Unit
-
-@kotlin.data() public final class A {
-    public constructor A(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String)
-    public final var y: kotlin.String
-    public final /*synthesized*/ fun component1(): kotlin.String
-    public final /*synthesized*/ fun copy(/*0*/ x: kotlin.Int, /*1*/ y: kotlin.String = ...): A
-    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/enum/enumWithAnnotationKeyword.kt

@@ -1,3 +1,3 @@
-data <!WRONG_MODIFIER_TARGET!>annotation<!> enum class E {
+<!WRONG_MODIFIER_TARGET!>annotation<!> enum class E {
     D
 }

compiler/testData/diagnostics/tests/enum/enumWithAnnotationKeyword.txt

@@ -1,12 +1,11 @@
 package
 
-@kotlin.data() @kotlin.annotation.annotation() public final enum class E : kotlin.Enum<E> {
+@kotlin.annotation.annotation() public final enum class E : kotlin.Enum<E> {
     enum entry D
 
     private constructor E()
     protected final override /*1*/ /*fake_override*/ fun clone(): kotlin.Any
     public final override /*1*/ /*fake_override*/ fun compareTo(/*0*/ other: E): kotlin.Int
-    public final /*synthesized*/ fun copy(): E
     public final override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public final override /*1*/ /*fake_override*/ fun name(): kotlin.String

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

@@ -3,10 +3,10 @@ data class A1(val x: String) {
     constructor(): this("")
 }
 
-data class A2() {
+data class A2(val y: String, val z: Int) {
-    constructor(x: String): this()
+    constructor(x: String): this(x, 0)
 }
 
-data class <!PRIMARY_CONSTRUCTOR_REQUIRED_FOR_DATA_CLASS!>A3<!> {
+data class <!PRIMARY_CONSTRUCTOR_REQUIRED_FOR_DATA_CLASS, DATA_CLASS_WITHOUT_PARAMETERS!>A3<!> {
     constructor()
 }

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

@@ -12,9 +12,13 @@ package
 }
 
 @kotlin.data() public final class A2 {
-    public constructor A2()
     public constructor A2(/*0*/ x: kotlin.String)
-    public final /*synthesized*/ fun copy(): A2
+    public constructor A2(/*0*/ y: kotlin.String, /*1*/ z: kotlin.Int)
+    public final val y: kotlin.String
+    public final val z: kotlin.Int
+    public final /*synthesized*/ fun component1(): kotlin.String
+    public final /*synthesized*/ fun component2(): kotlin.Int
+    public final /*synthesized*/ fun copy(/*0*/ y: kotlin.String = ..., /*1*/ z: kotlin.Int = ...): A2
     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/JetDiagnosticsTestGenerated.java

@@ -3294,12 +3294,6 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/diagnostics/tests/dataClasses"), Pattern.compile("^(.+)\\.kt$"), true);
             }
 
-            @TestMetadata("bothParamsAreNotProperties.kt")
-            public void testBothParamsAreNotProperties() throws Exception {
-                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/bothParamsAreNotProperties.kt");
-                doTest(fileName);
-            }
-
             @TestMetadata("componentFunctionInSubClass.kt")
             public void testComponentFunctionInSubClass() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/componentFunctionInSubClass.kt");
@@ -3330,6 +3324,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
+            @TestMetadata("dataClassVarargParam.kt")
+            public void testDataClassVarargParam() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataClassVarargParam.kt");
+                doTest(fileName);
+            }
+
             @TestMetadata("dataInheritance.kt")
             public void testDataInheritance() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/dataInheritance.kt");
@@ -3342,18 +3342,6 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
-            @TestMetadata("firstParamIsVal.kt")
-            public void testFirstParamIsVal() throws Exception {
-                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/firstParamIsVal.kt");
-                doTest(fileName);
-            }
-
-            @TestMetadata("firstParamIsVar.kt")
-            public void testFirstParamIsVar() throws Exception {
-                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/firstParamIsVar.kt");
-                doTest(fileName);
-            }
-
             @TestMetadata("implementTraitWhichHasComponent1.kt")
             public void testImplementTraitWhichHasComponent1() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/implementTraitWhichHasComponent1.kt");
@@ -3402,12 +3390,6 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
-            @TestMetadata("paramNameSameToField.kt")
-            public void testParamNameSameToField() throws Exception {
-                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/paramNameSameToField.kt");
-                doTest(fileName);
-            }
-
             @TestMetadata("repeatedProperties.kt")
             public void testRepeatedProperties() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/repeatedProperties.kt");
@@ -3420,18 +3402,6 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                 doTest(fileName);
             }
 
-            @TestMetadata("secondParamIsVal.kt")
-            public void testSecondParamIsVal() throws Exception {
-                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/secondParamIsVal.kt");
-                doTest(fileName);
-            }
-
-            @TestMetadata("secondParamIsVar.kt")
-            public void testSecondParamIsVar() throws Exception {
-                String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/secondParamIsVar.kt");
-                doTest(fileName);
-            }
-
             @TestMetadata("twoValParams.kt")
             public void testTwoValParams() throws Exception {
                 String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/dataClasses/twoValParams.kt");

idea/testData/checker/rendering/TypeInferenceError.kt

@@ -8,4 +8,4 @@ fun foo() {
 //extract from library
 fun <K, V> hashMap(<warning>p</warning>: Pair<K, V>): MutableMap<K, V> {<error>}</error>
 fun <K, V> K.to(<warning>v</warning>: V): Pair<K, V> {<error>}</error>
-data class Pair<K, V> {}
+class Pair<K, V> {}