deprecate required classes for traits

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

@@ -188,6 +188,8 @@ public interface Errors {
 
     DiagnosticFactory0<JetDelegatorByExpressionSpecifier> DELEGATION_IN_TRAIT = DiagnosticFactory0.create(ERROR);
 
+    DiagnosticFactory0<PsiElement> TRAIT_WITH_SUPERCLASS = DiagnosticFactory0.create(WARNING);
+
     DiagnosticFactory2<JetNamedDeclaration, ClassDescriptor, ClassDescriptor> UNMET_TRAIT_REQUIREMENT =
             DiagnosticFactory2.create(ERROR, PositioningStrategies.DECLARATION_NAME);
 

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

@@ -385,6 +385,7 @@ public class DefaultErrorMessages {
         MAP.put(SUPERTYPE_INITIALIZED_IN_TRAIT, "Traits cannot initialize supertypes");
         MAP.put(CLASS_IN_SUPERTYPE_FOR_ENUM, "Enum class cannot inherit from classes");
         MAP.put(CONSTRUCTOR_IN_TRAIT, "A trait may not have a constructor");
+        MAP.put(TRAIT_WITH_SUPERCLASS, "Specifying a required base class for trait implementations is deprecated");
         MAP.put(SUPERTYPE_APPEARS_TWICE, "A supertype appears twice");
         MAP.put(FINAL_SUPERTYPE, "This type is final, so it cannot be inherited from");
         MAP.put(SINGLETON_IN_SUPERTYPE, "Cannot inherit from a singleton");

compiler/frontend/src/org/jetbrains/kotlin/resolve/BodyResolver.java

@@ -416,6 +416,10 @@ public class BodyResolver {
                     if (supertypeOwner.getKind() == ClassKind.ENUM_CLASS) {
                         trace.report(CLASS_IN_SUPERTYPE_FOR_ENUM.on(typeReference));
                     }
+                    else if (supertypeOwner.getKind() == ClassKind.TRAIT &&
+                             !classAppeared && !TypesPackage.isDynamic(supertype) /* avoid duplicate diagnostics */) {
+                        trace.report(TRAIT_WITH_SUPERCLASS.on(typeReference));
+                    }
                     if (classAppeared) {
                         trace.report(MANY_CLASSES_IN_SUPERTYPE_LIST.on(typeReference));
                     }

compiler/testData/diagnostics/tests/DiamondFunction.kt

@@ -1,8 +1,8 @@
-open class Base() {
+trait Base {
     fun f() = 1
 }
     
-open class Left() : Base()
+open class Left() : Base
 
 trait Right : Base
 

compiler/testData/diagnostics/tests/DiamondFunction.txt

@@ -1,9 +1,8 @@
 package
 
-internal open class Base {
+internal trait Base {
-    public constructor Base()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final fun f(): kotlin.Int
+    internal open fun f(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -11,7 +10,7 @@ internal open class Base {
 internal final class Diamond : Left, Right {
     public constructor Diamond()
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final override /*2*/ /*fake_override*/ fun f(): kotlin.Int
+    internal open override /*2*/ /*fake_override*/ fun f(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -19,14 +18,14 @@ internal final class Diamond : Left, Right {
 internal open class Left : Base {
     public constructor Left()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final override /*1*/ /*fake_override*/ fun f(): kotlin.Int
+    internal open override /*1*/ /*fake_override*/ fun f(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 internal trait Right : Base {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final override /*1*/ /*fake_override*/ fun f(): kotlin.Int
+    internal open override /*1*/ /*fake_override*/ fun f(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }

compiler/testData/diagnostics/tests/DiamondFunctionGeneric.kt

@@ -1,8 +1,8 @@
-open class Base<P>() {
+trait Base<P> {
     fun f() = 1
 }
     
-open class Left<P>() : Base<P>()
+open class Left<P>() : Base<P>
 
 trait Right<P> : Base<P>
 

compiler/testData/diagnostics/tests/DiamondFunctionGeneric.txt

@@ -1,9 +1,8 @@
 package
 
-internal open class Base</*0*/ P> {
+internal trait Base</*0*/ P> {
-    public constructor Base</*0*/ P>()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final fun f(): kotlin.Int
+    internal open fun f(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -11,7 +10,7 @@ internal open class Base</*0*/ P> {
 internal final class Diamond</*0*/ P> : Left<P>, Right<P> {
     public constructor Diamond</*0*/ P>()
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final override /*2*/ /*fake_override*/ fun f(): kotlin.Int
+    internal open override /*2*/ /*fake_override*/ fun f(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -19,14 +18,14 @@ internal final class Diamond</*0*/ P> : Left<P>, Right<P> {
 internal open class Left</*0*/ P> : Base<P> {
     public constructor Left</*0*/ P>()
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final override /*1*/ /*fake_override*/ fun f(): kotlin.Int
+    internal open override /*1*/ /*fake_override*/ fun f(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 internal trait Right</*0*/ P> : Base<P> {
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    internal final override /*1*/ /*fake_override*/ fun f(): kotlin.Int
+    internal open override /*1*/ /*fake_override*/ fun f(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }

compiler/testData/diagnostics/tests/DiamondProperty.kt

@@ -1,9 +1,10 @@
-
+trait Base {
-open class Base() {
+    var v : Int
-    var v : Int = 0
+        get() = 1
+        set(v) {}
 }
     
-open class Left() : Base()
+open class Left() : Base
 
 trait Right : Base
 

compiler/testData/diagnostics/tests/DiamondProperty.txt

@@ -1,8 +1,7 @@
 package
 
-internal open class Base {
+internal trait Base {
-    public constructor Base()
+    internal open var v: kotlin.Int
-    internal final var v: kotlin.Int
     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
@@ -10,7 +9,7 @@ internal open class Base {
 
 internal final class Diamond : Left, Right {
     public constructor Diamond()
-    internal final override /*2*/ /*fake_override*/ var v: kotlin.Int
+    internal open override /*2*/ /*fake_override*/ var v: kotlin.Int
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
@@ -18,14 +17,14 @@ internal final class Diamond : Left, Right {
 
 internal open class Left : Base {
     public constructor Left()
-    internal final override /*1*/ /*fake_override*/ var v: kotlin.Int
+    internal open override /*1*/ /*fake_override*/ var v: kotlin.Int
     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
 }
 
 internal trait Right : Base {
-    internal final override /*1*/ /*fake_override*/ var v: kotlin.Int
+    internal open override /*1*/ /*fake_override*/ var v: kotlin.Int
     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/SupertypeListChecks.kt

@@ -24,17 +24,17 @@ trait T2<T> {}
 trait Test<!CONSTRUCTOR_IN_TRAIT!>()<!> {
 }
 
-trait Test1 : C2<!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!> {}
+trait Test1 : <!TRAIT_WITH_SUPERCLASS!>C2<!><!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!> {}
 
-trait Test2 : C2 {}
+trait Test2 : <!TRAIT_WITH_SUPERCLASS!>C2<!> {}
 
-trait Test3 : C2, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>C3<!> {}
+trait Test3 : <!TRAIT_WITH_SUPERCLASS!>C2<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>C3<!> {}
 
 trait Test4 : T1 {}
 
 trait Test5 : T1, <!SUPERTYPE_APPEARS_TWICE!>T1<!> {}
 
-trait Test6 : <!FINAL_SUPERTYPE!>C1<!> {}
+trait Test6 : <!TRAIT_WITH_SUPERCLASS, FINAL_SUPERTYPE!>C1<!> {}
 
 class CTest1() : OC1() {}
 

compiler/testData/diagnostics/tests/TraitOverrideObjectMethods.kt

@@ -1,4 +1,4 @@
-trait MyTrait: <!PLATFORM_CLASS_MAPPED_TO_KOTLIN!>Object<!> {
+trait MyTrait: <!PLATFORM_CLASS_MAPPED_TO_KOTLIN, TRAIT_WITH_SUPERCLASS!>Object<!> {
     override fun toString(): String
     public override fun finalize()
     public <!OVERRIDING_FINAL_MEMBER!>override<!> fun wait()

compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/require.kt

@@ -2,6 +2,6 @@ open class C {
     val x = 1
 }
 
-trait Tr : C {
+trait Tr : <!TRAIT_WITH_SUPERCLASS!>C<!> {
     <!ACCIDENTAL_OVERRIDE!>fun getX()<!> = 1
 }

compiler/testData/diagnostics/tests/nullableTypes/redundantNullableInSupertype.kt

@@ -1,4 +1,5 @@
-trait X: Any<!NULLABLE_SUPERTYPE!>?<!><!REDUNDANT_NULLABLE!>?<!> {
+trait A
+trait X: A<!NULLABLE_SUPERTYPE!>?<!><!REDUNDANT_NULLABLE!>?<!> {
 
 }
 

compiler/testData/diagnostics/tests/nullableTypes/redundantNullableInSupertype.txt

@@ -2,7 +2,13 @@ package
 
 internal fun </*0*/ T> interaction(/*0*/ t: T): kotlin.Unit
 
-internal trait X {
+internal trait 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
+}
+
+internal trait X : 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/override/kt1862.kt

@@ -6,6 +6,6 @@ open class Bbb() : Aaa() {
     override fun foo() = 2
 }
 
-trait Ccc : Aaa
+trait Ccc : <!TRAIT_WITH_SUPERCLASS!>Aaa<!>
 
 class Ddd() : Bbb(), Ccc

compiler/testData/diagnostics/tests/regressions/kt307.kt

@@ -4,7 +4,7 @@ open class AL {
     fun get(i : Int) : Any? = i
 }
 
-trait ALE<T> : AL {
+trait ALE<T> : <!TRAIT_WITH_SUPERCLASS!>AL<!> {
 fun getOrNull(index: Int, value: T) : T {
 return <!UNCHECKED_CAST!>get(index) as? T<!> ?: value
 }

compiler/testData/diagnostics/tests/thisAndSuper/notAccessibleSuperInTrait.kt

@@ -2,7 +2,7 @@ open class A {
     open fun foo() {}
 }
 
-trait ATrait : A {
+trait ATrait : <!TRAIT_WITH_SUPERCLASS!>A<!> {
 
     override fun foo() {
         <!SUPERCLASS_NOT_ACCESSIBLE_FROM_TRAIT!>super<A><!>.foo()

compiler/testData/diagnostics/tests/traitWithRequired/abstractClass.kt

@@ -1,6 +1,6 @@
 open class Required
 
-trait Trait : Required
+trait Trait : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 abstract <!UNMET_TRAIT_REQUIREMENT!>class Abstract<!> : Trait
 

compiler/testData/diagnostics/tests/traitWithRequired/anonymousObjectExtendsTraitWithRequired.kt

@@ -1,6 +1,6 @@
 open class Required
 
-trait A : Required
+trait A : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 val a = <!UNMET_TRAIT_REQUIREMENT!>object<!> : A {}
 val b: A = object : A, Required() {}

compiler/testData/diagnostics/tests/traitWithRequired/differentGenericArguments.kt

@@ -1,8 +1,8 @@
 open class Generic<T>
 
-trait A : Generic<Int>
+trait A : <!TRAIT_WITH_SUPERCLASS!>Generic<Int><!>
 
-trait B : Generic<String>
+trait B : <!TRAIT_WITH_SUPERCLASS!>Generic<String><!>
 
 <!UNMET_TRAIT_REQUIREMENT, UNMET_TRAIT_REQUIREMENT!>class Y<!> : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B<!>
 class Z : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B, Generic<Int>()<!>

compiler/testData/diagnostics/tests/traitWithRequired/kt3006.kt

@@ -1,7 +1,7 @@
 open class Base {
 }
 
-trait Derived: Base {
+trait Derived: <!TRAIT_WITH_SUPERCLASS!>Base<!> {
     fun foo() {
         f1(this@Derived)
     }

compiler/testData/diagnostics/tests/traitWithRequired/manyRequirementsDisallowed.kt

@@ -1,4 +1,4 @@
 open class A
 open class B
 
-trait C : A, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>B<!>
+trait C : <!TRAIT_WITH_SUPERCLASS!>A<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST!>B<!>

compiler/testData/diagnostics/tests/traitWithRequired/manyTraitsRequireSameClass.kt

@@ -1,12 +1,12 @@
 open class Required
 
-trait A : Required
+trait A : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait B : A, Required
+trait B : A, <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait C : Required
+trait C : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
-trait D : B, Required
+trait D : B, <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 <!UNMET_TRAIT_REQUIREMENT, UNMET_TRAIT_REQUIREMENT, UNMET_TRAIT_REQUIREMENT!>class W<!> : D
 class X : D, Required()

compiler/testData/diagnostics/tests/traitWithRequired/requirementFulfilledBySubclass.kt

@@ -1,6 +1,6 @@
 open class RequiredBase
 
-trait Trait : RequiredBase
+trait Trait : <!TRAIT_WITH_SUPERCLASS!>RequiredBase<!>
 
 open class RequiredDerived : RequiredBase()
 

compiler/testData/diagnostics/tests/traitWithRequired/traitExtendsTraitWithRequired.kt

@@ -1,6 +1,6 @@
 open class Required(val value: String)
 
-trait First : Required
+trait First : <!TRAIT_WITH_SUPERCLASS!>Required<!>
 
 trait Second : First
 

compiler/testData/diagnostics/tests/traitWithRequired/traitRequiresAny.kt

@@ -1,4 +1,4 @@
-trait AnyTrait : Any
+trait AnyTrait : <!TRAIT_WITH_SUPERCLASS!>Any<!>
 
 class Foo : AnyTrait
 

compiler/testData/diagnostics/tests/traitWithRequired/traitSupertypeList.kt

@@ -1,9 +1,9 @@
 open class bar()
 
-trait Foo<!CONSTRUCTOR_IN_TRAIT!>()<!> : bar<!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!> {
+trait Foo<!CONSTRUCTOR_IN_TRAIT!>()<!> : <!TRAIT_WITH_SUPERCLASS!>bar<!><!SUPERTYPE_INITIALIZED_IN_TRAIT!>()<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!>, <!MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!> {
 }
 
-trait Foo2 : bar, Foo {
+trait Foo2 : <!TRAIT_WITH_SUPERCLASS!>bar<!>, Foo {
 }
 
 open class Foo1() : bar(), <!SUPERTYPE_NOT_INITIALIZED, MANY_CLASSES_IN_SUPERTYPE_LIST, SUPERTYPE_APPEARS_TWICE!>bar<!>, Foo, <!SUPERTYPE_APPEARS_TWICE!>Foo<!><!NO_CONSTRUCTOR!>()<!> {}

compiler/testData/diagnostics/tests/traitWithRequired/uninheritableTraitDifferentGenericArguments.kt

@@ -1,7 +1,7 @@
 open class Generic<T>
 
-trait A : Generic<String>
+trait A : <!TRAIT_WITH_SUPERCLASS!>Generic<String><!>
 
-trait B : Generic<Int>
+trait B : <!TRAIT_WITH_SUPERCLASS!>Generic<Int><!>
 
 trait C : <!INCONSISTENT_TYPE_PARAMETER_VALUES!>A, B<!>

idea/testData/checker/SupertypeListChecks.kt

@@ -24,11 +24,11 @@ trait T2<T> {}
 trait Test<error>()</error> {
 }
 
-trait Test1 : C2<error>()</error> {}
+trait Test1 : <warning>C2</warning><error>()</error> {}
 
-trait Test2 : C2 {}
+trait Test2 : <warning>C2</warning> {}
 
-trait Test3 : C2, <error>C3</error> {}
+trait Test3 : <warning>C2</warning>, <error>C3</error> {}
 
 trait Test4 : T1 {}
 

idea/testData/checker/TraitSupertypeList.kt

@@ -1,9 +1,9 @@
 open class bar()
 
-trait Foo<error>()</error> : bar<error>()</error>, <error>bar</error>, <error>bar</error> {
+trait Foo<error>()</error> : <warning>bar</warning><error>()</error>, <error><error>bar</error></error>, <error><error>bar</error></error> {
 }
 
-trait Foo2 : bar, Foo {
+trait Foo2 : <warning>bar</warning>, Foo {
 }
 
 open class Foo1() : bar(), <error>bar</error>, Foo, <error>Foo</error><error>()</error> {}

idea/testData/checker/unmetTraitRequirements.kt

@@ -1,14 +1,14 @@
 open class Base {
 }
 
-trait Derived: Base {
+trait Derived: <warning>Base</warning> {
     fun foo() {
         f1(this@Derived)
     }
 }
 
-<error descr="[UNMET_TRAIT_REQUIREMENT] Super trait 'Derived' requires subclasses to extend 'Base'">class DerivedImpl</error>(): Derived {}
+<error>class DerivedImpl</error>(): Derived {}
-<error descr="[UNMET_TRAIT_REQUIREMENT] Super trait 'Derived' requires subclasses to extend 'Base'">object ObjectImpl</error>: Derived {}
+<error>object ObjectImpl</error>: Derived {}
 
 fun f1(b: Base) = b