KT-1934 & KT-10197:

Naive approximation for fake overriding signature:
use upper bound for flexible types.
Check delegation errors.

compiler/testData/diagnostics/tests/delegation/Delegation_ClashingFunctions.kt

@@ -10,9 +10,9 @@ interface Three {
     public fun foo(): String
 }
 
-<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class Test123<!>(val v1: One, val v2: Two, val v3: Three) : One by v1, Two by v2, Three by v3 { }
-<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class Test132<!>(val v1: One, val v2: Two, val v3: Three) : One by v1, Three by v3, Two by v2 { }
+<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test123<!>(val v1: One, val v2: Two, val v3: Three) : One by v1, Two by v2, Three by v3 { }
+<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test132<!>(val v1: One, val v2: Two, val v3: Three) : One by v1, Three by v3, Two by v2 { }
 <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class Test312<!>(val v1: One, val v2: Two, val v3: Three) : Three by v3, One by v1, Two by v2 { }
 <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class Test321<!>(val v1: One, val v2: Two, val v3: Three) : Three by v3, Two by v2, One by v1 { }
-<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class Test231<!>(val v1: One, val v2: Two, val v3: Three) : Two by v2, Three by v3, One by v1 { }
-<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class Test213<!>(val v1: One, val v2: Two, val v3: Three) : Two by v2, One by v1, Three by v3 { }
+<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test231<!>(val v1: One, val v2: Two, val v3: Three) : Two by v2, Three by v3, One by v1 { }
+<!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, MANY_IMPL_MEMBER_NOT_IMPLEMENTED, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test213<!>(val v1: One, val v2: Two, val v3: Three) : Two by v2, One by v1, Three by v3 { }

compiler/testData/diagnostics/tests/delegation/clashes/returnTypeMismatch.kt

@@ -0,0 +1,44 @@
+interface IStr {
+    fun foo(): String
+}
+
+class CStr : IStr {
+    override fun foo(): String = ""
+}
+
+interface IInt {
+    fun foo(): Int
+}
+
+class CInt : IInt {
+    override fun foo(): Int = 42
+}
+
+interface IGeneric<T> {
+    fun foo(): T
+}
+
+class CGeneric<T> : IGeneric<T> {
+    override fun foo(): T {
+        throw UnsupportedOperationException()
+    }
+}
+
+abstract <!RETURN_TYPE_MISMATCH_ON_INHERITANCE, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test1<!> : IStr by CStr(), IInt
+
+abstract <!RETURN_TYPE_MISMATCH_ON_INHERITANCE, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test2<!> : IStr, IInt by CInt()
+
+abstract <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED, RETURN_TYPE_MISMATCH_ON_INHERITANCE, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test3<!> : IStr by CStr(), IInt by CInt()
+
+abstract class Test4 : IStr by CStr(), IGeneric<String>
+
+abstract class Test5 : IStr by CStr(), IGeneric<Any>
+
+abstract <!RETURN_TYPE_MISMATCH_ON_INHERITANCE, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test6<!> : IStr by CStr(), IGeneric<Int>
+
+abstract class Test7 : IGeneric<String> by CGeneric<String>(), IStr
+
+abstract <!RETURN_TYPE_MISMATCH_ON_INHERITANCE, RETURN_TYPE_MISMATCH_ON_OVERRIDE_BY_DELEGATION!>class Test8<!> : IGeneric<String> by CGeneric<String>(), IInt
+
+// Can't test right now due to https://youtrack.jetbrains.com/issue/KT-10258
+// abstract class Test9 : IGeneric<String> by CGeneric<String>(), IGeneric<Int>

compiler/testData/diagnostics/tests/delegation/clashes/returnTypeMismatch.txt

@@ -0,0 +1,110 @@
+package
+
+public final class CGeneric</*0*/ T> : IGeneric<T> {
+    public constructor CGeneric</*0*/ T>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun foo(): T
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class CInt : IInt {
+    public constructor CInt()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun foo(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class CStr : IStr {
+    public constructor CStr()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun foo(): kotlin.String
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface IGeneric</*0*/ T> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): T
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface IInt {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface IStr {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.String
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test1 : IStr, IInt {
+    public constructor Test1()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test2 : IStr, IInt {
+    public constructor Test2()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test3 : IStr, IInt {
+    public constructor Test3()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test4 : IStr, IGeneric<kotlin.String> {
+    public constructor Test4()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test5 : IStr, IGeneric<kotlin.Any> {
+    public constructor Test5()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test6 : IStr, IGeneric<kotlin.Int> {
+    public constructor Test6()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test7 : IGeneric<kotlin.String>, IStr {
+    public constructor Test7()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class Test8 : IGeneric<kotlin.String>, IInt {
+    public constructor Test8()
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*2*/ /*delegation*/ fun foo(): kotlin.String
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/j+k/collectionOverrides/irrelevantImplMutableListKotlin.txt

@@ -13,7 +13,7 @@ public open class A : AImpl, kotlin.MutableList<kotlin.String!> {
     public final override /*2*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.String!): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public final override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String!
+    public final override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public final override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String!): kotlin.Int
     public final override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
@@ -25,7 +25,7 @@ public open class A : AImpl, kotlin.MutableList<kotlin.String!> {
     public final override /*2*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public final override /*2*/ /*fake_override*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.String
     public final override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
-    public final override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.String!
+    public final override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String): kotlin.String
     public final override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String!>
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -69,7 +69,7 @@ public final class X : A {
     public final override /*1*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.String!): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public final override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String!
+    public final override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.String
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public final override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.String!): kotlin.Int
     public final override /*1*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
@@ -81,7 +81,7 @@ public final class X : A {
     public final override /*1*/ /*fake_override*/ fun removeAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
     public final override /*1*/ /*fake_override*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.String
     public final override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.String!>): kotlin.Boolean
-    public final override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String!): kotlin.String!
+    public final override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.String): kotlin.String
     public final override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.String!>
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }

compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAt.txt

@@ -53,7 +53,7 @@ public abstract class B</*0*/ T> : kotlin.MutableList<T>, java.util.AbstractList
     public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: T!): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<T!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): T!
+    public abstract override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): T
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: T!): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
@@ -68,7 +68,7 @@ public abstract class B</*0*/ T> : kotlin.MutableList<T>, java.util.AbstractList
     public open override /*2*/ fun removeAt(/*0*/ index: kotlin.Int): T
     protected/*protected and package*/ open override /*1*/ /*fake_override*/ fun removeRange(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<T!>): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: T!): T!
+    public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: T): T
     public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<T!>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
     public open override /*1*/ /*fake_override*/ fun </*0*/ T : kotlin.Any!> toArray(/*0*/ p0: kotlin.Array<(out) T!>!): kotlin.Array<(out) T!>!

compiler/testData/diagnostics/tests/j+k/collectionOverrides/removeAtInt.txt

@@ -14,7 +14,7 @@ public abstract class A : B {
     public open override /*1*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.Int!): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
     public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.Int!
+    public abstract override /*1*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.Int!): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
@@ -29,7 +29,7 @@ public abstract class A : B {
     public open override /*1*/ fun removeAt(/*0*/ x: kotlin.Int): kotlin.Int
     protected/*protected and package*/ open override /*1*/ /*fake_override*/ fun removeRange(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int): kotlin.Unit
     public open override /*1*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
-    public open override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int!): kotlin.Int!
+    public open override /*1*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.Int!>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
     public open override /*1*/ /*fake_override*/ fun </*0*/ T : kotlin.Any!> toArray(/*0*/ p0: kotlin.Array<(out) T!>!): kotlin.Array<(out) T!>!
@@ -53,7 +53,7 @@ public abstract class B : kotlin.MutableList<kotlin.Int>, java.util.AbstractList
     public open override /*2*/ /*fake_override*/ fun contains(/*0*/ element: kotlin.Int!): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun containsAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.Int!
+    public abstract override /*2*/ /*fake_override*/ fun get(/*0*/ index: kotlin.Int): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun indexOf(/*0*/ element: kotlin.Int!): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun isEmpty(): kotlin.Boolean
@@ -68,7 +68,7 @@ public abstract class B : kotlin.MutableList<kotlin.Int>, java.util.AbstractList
     public open override /*2*/ fun removeAt(/*0*/ index: kotlin.Int): kotlin.Int
     protected/*protected and package*/ open override /*1*/ /*fake_override*/ fun removeRange(/*0*/ p0: kotlin.Int, /*1*/ p1: kotlin.Int): kotlin.Unit
     public open override /*2*/ /*fake_override*/ fun retainAll(/*0*/ elements: kotlin.Collection<kotlin.Int!>): kotlin.Boolean
-    public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int!): kotlin.Int!
+    public open override /*2*/ /*fake_override*/ fun set(/*0*/ index: kotlin.Int, /*1*/ element: kotlin.Int): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun subList(/*0*/ fromIndex: kotlin.Int, /*1*/ toIndex: kotlin.Int): kotlin.MutableList<kotlin.Int!>
     public open override /*1*/ /*fake_override*/ fun toArray(): kotlin.Array<(out) kotlin.Any!>!
     public open override /*1*/ /*fake_override*/ fun </*0*/ T : kotlin.Any!> toArray(/*0*/ p0: kotlin.Array<(out) T!>!): kotlin.Array<(out) T!>!

compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnType.kt

@@ -21,10 +21,7 @@ interface KDerived2a : K2, J
 interface KDerived2b : J, K2
 
 interface KDerived12a : K1, K2, J
-// public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String!
 
-<!RETURN_TYPE_MISMATCH_ON_INHERITANCE!>interface KDerived12b<!> : K1, J, K2 // TODO
-// public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String?
+interface KDerived12b : K1, J, K2
 
-interface KDerived12c : J, K1, K2
-// public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String
+interface KDerived12c : J, K1, K2

compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnType.txt

@@ -25,14 +25,14 @@ public interface K2 {
 
 public interface KDerived12a : K1, K2, J {
     public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String!
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
 }
 
 public interface KDerived12b : K1, J, K2 {
     public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String?
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.String
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
 }
@@ -46,7 +46,7 @@ public interface KDerived12c : J, K1, K2 {
 
 public interface KDerived1a : K1, J {
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(): kotlin.String!
+    public abstract override /*2*/ /*fake_override*/ fun foo(): kotlin.String
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }

compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeIn.kt

@@ -0,0 +1,63 @@
+// FILE: InOut.k
+interface In<in T>
+interface Out<out T>
+interface Inv<T>
+
+// FILE: J1.java
+public interface J1 {
+    In<String> foo();
+}
+
+// FILE: J2.java
+import org.jetbrains.annotations.*;
+
+public interface J2 {
+    @NotNull In<String> foo();
+}
+
+// FILE: J3.java
+import org.jetbrains.annotations.*;
+
+public interface J3 {
+    @Nullable In<String> foo();
+}
+
+// FILE: K.kt
+interface K1 {
+    fun foo(): In<String>
+}
+
+interface K2 {
+    fun foo(): In<String?>
+}
+
+// FIXME TestJ1K1 should have foo(): In<String!>, since In<String!> <: In<String>.
+interface TestJ1K1 : J1, K1
+interface TestK1J1 : K1, J1
+
+interface TestJ1K2 : J1, K2
+interface TestK2J1 : K2, J1
+
+interface TestJ2K1 : J2, K1
+interface TestK1J2 : K1, J2
+
+interface TestJ2K2 : J2, K2
+interface TestK2J2 : K2, J2
+
+interface TestJ3K1 : J3, K1
+interface TestK1J3 : K1, J3
+
+interface TestJ3K2 : J3, K2
+interface TestK2J3 : K2, J3
+
+interface TestJ1K1K2 : J1, K1, K2
+interface TestK1J1K2 : K1, J1, K2
+interface TestK1K2J1 : K1, K2, J1
+
+interface TestJ2K1K2 : J2, K1, K2
+interface TestK1J2K2 : K1, J2, K2
+interface TestK1K2J2 : K1, K2, J2
+
+interface TestJ3K1K2 : J3, K1, K2
+interface TestK1J3K2 : K1, J3, K2
+interface TestK1K2J3 : K1, K2, J3

compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeIn.txt

@@ -0,0 +1,205 @@
+package
+
+public /*synthesized*/ fun J1(/*0*/ function: () -> In<kotlin.String!>!): J1
+public /*synthesized*/ fun J2(/*0*/ function: () -> In<kotlin.String!>!): J2
+public /*synthesized*/ fun J3(/*0*/ function: () -> In<kotlin.String!>!): J3
+
+public interface In</*0*/ in 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
+}
+
+public interface Inv</*0*/ 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
+}
+
+public interface J1 {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): In<kotlin.String!>!
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface J2 {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    @org.jetbrains.annotations.NotNull() public abstract fun foo(): In<kotlin.String!>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface J3 {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    @org.jetbrains.annotations.Nullable() public abstract fun foo(): In<kotlin.String!>?
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface K1 {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): In<kotlin.String>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface K2 {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): In<kotlin.String?>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Out</*0*/ out 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
+}
+
+public interface TestJ1K1 : J1, K1 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ1K1K2 : J1, K1, K2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ1K2 : J1, K2 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ2K1 : J2, K1 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ2K1K2 : J2, K1, K2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ2K2 : J2, K2 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ3K1 : J3, K1 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ3K1K2 : J3, K1, K2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestJ3K2 : J3, K2 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1J1 : K1, J1 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1J1K2 : K1, J1, K2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1J2 : K1, J2 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    @org.jetbrains.annotations.NotNull() public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String!>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1J2K2 : K1, J2, K2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1J3 : K1, J3 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1J3K2 : K1, J3, K2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1K2J1 : K1, K2, J1 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1K2J2 : K1, K2, J2 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    @org.jetbrains.annotations.NotNull() public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String!>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK1K2J3 : K1, K2, J3 {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK2J1 : K2, J1 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK2J2 : K2, J2 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    @org.jetbrains.annotations.NotNull() public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String!>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface TestK2J3 : K2, J3 {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): In<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeList.kt

@@ -0,0 +1,37 @@
+// FILE: J.java
+public interface J {
+    java.util.List<String> foo();
+}
+
+// FILE: K.kt
+interface ILNS {
+    fun foo(): List<String?>
+}
+
+interface IMLS {
+    fun foo(): MutableList<String>
+}
+
+interface IMLNS {
+    fun foo(): MutableList<String?>
+}
+
+interface ILS {
+    fun foo(): List<String>
+}
+
+interface Test1 : ILNS, J
+interface Test2 : J, ILNS
+
+interface Test3 : IMLS, J
+interface Test4 : J, IMLS
+
+interface Test5 : ILNS, IMLS, J
+interface Test6 : ILNS, J, IMLS
+interface Test7 : J, ILNS, IMLS
+
+// ILS and IMLNS are incompatible
+
+<!RETURN_TYPE_MISMATCH_ON_INHERITANCE!>interface Test8<!> : J, IMLNS, ILS
+<!RETURN_TYPE_MISMATCH_ON_INHERITANCE!>interface Test9<!> : IMLNS, J, ILS
+<!RETURN_TYPE_MISMATCH_ON_INHERITANCE!>interface Test10<!> : IMLNS, ILS, J

compiler/testData/diagnostics/tests/override/clashesOnInheritance/flexibleReturnTypeList.txt

@@ -0,0 +1,108 @@
+package
+
+public /*synthesized*/ fun J(/*0*/ function: () -> kotlin.(Mutable)List<kotlin.String!>!): J
+
+public interface ILNS {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.List<kotlin.String?>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface ILS {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.List<kotlin.String>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface IMLNS {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.MutableList<kotlin.String?>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface IMLS {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface J {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.(Mutable)List<kotlin.String!>!
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test1 : ILNS, J {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): kotlin.List<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test10 : IMLNS, ILS, J {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test2 : J, ILNS {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): kotlin.List<kotlin.String?>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test3 : IMLS, J {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test4 : J, IMLS {
+    public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*2*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test5 : ILNS, IMLS, J {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test6 : ILNS, J, IMLS {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test7 : J, ILNS, IMLS {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test8 : J, IMLNS, ILS {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test9 : IMLNS, J, ILS {
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract override /*3*/ /*fake_override*/ fun foo(): kotlin.MutableList<kotlin.String?>
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/override/clashesOnInheritance/varTypeMismatch.kt

@@ -0,0 +1,29 @@
+open class A {
+    open var foo: Boolean = true
+}
+
+interface IA {
+    var foo: String
+}
+
+interface IAA {
+    var foo: Int
+}
+
+interface IGA<T> {
+    var foo: T
+}
+
+<!PROPERTY_TYPE_MISMATCH_ON_INHERITANCE!>class B1<!>: A(), IA
+
+<!PROPERTY_TYPE_MISMATCH_ON_INHERITANCE!>class B2<!>: A(), IA, IAA
+
+abstract <!PROPERTY_TYPE_MISMATCH_ON_INHERITANCE!>class B3<!>: IA, IAA
+
+class BS1: A(), IGA<Boolean>
+
+<!PROPERTY_TYPE_MISMATCH_ON_INHERITANCE!>class BS2<!>: A(), IGA<Any>
+
+<!PROPERTY_TYPE_MISMATCH_ON_INHERITANCE!>class BS3<!>: A(), IGA<String>
+
+<!PROPERTY_TYPE_MISMATCH_ON_INHERITANCE!>class BG1<!><T>: A(), IGA<T>

compiler/testData/diagnostics/tests/override/clashesOnInheritance/varTypeMismatch.txt

@@ -0,0 +1,86 @@
+package
+
+public open class A {
+    public constructor A()
+    public open var foo: kotlin.Boolean
+    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
+}
+
+public final class B1 : A, IA {
+    public constructor B1()
+    public open override /*2*/ /*fake_override*/ var foo: kotlin.Boolean
+    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
+}
+
+public final class B2 : A, IA, IAA {
+    public constructor B2()
+    public open override /*3*/ /*fake_override*/ var foo: kotlin.Boolean
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class B3 : IA, IAA {
+    public constructor B3()
+    public abstract override /*2*/ /*fake_override*/ var foo: kotlin.String
+    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
+}
+
+public final class BG1</*0*/ T> : A, IGA<T> {
+    public constructor BG1</*0*/ T>()
+    public open override /*2*/ /*fake_override*/ var foo: kotlin.Boolean
+    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
+}
+
+public final class BS1 : A, IGA<kotlin.Boolean> {
+    public constructor BS1()
+    public open override /*2*/ /*fake_override*/ var foo: kotlin.Boolean
+    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
+}
+
+public final class BS2 : A, IGA<kotlin.Any> {
+    public constructor BS2()
+    public open override /*2*/ /*fake_override*/ var foo: kotlin.Boolean
+    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
+}
+
+public final class BS3 : A, IGA<kotlin.String> {
+    public constructor BS3()
+    public open override /*2*/ /*fake_override*/ var foo: kotlin.Boolean
+    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
+}
+
+public interface IA {
+    public abstract var foo: kotlin.String
+    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
+}
+
+public interface IAA {
+    public abstract var foo: 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
+}
+
+public interface IGA</*0*/ T> {
+    public abstract var foo: 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/syntheticExtensions/javaProperties/KotlinOverridesJava.kt

@@ -24,7 +24,7 @@ fun foo(k: KotlinClass) {
     k.setSomething4("")
     k.something4 += ""
     k.setSomething4(<!NULL_FOR_NONNULL_TYPE!>null<!>)
-    k.something4 = null
+    k.something4 = <!NULL_FOR_NONNULL_TYPE!>null<!>
 
     useString(k.getSomething5())
     useString(k.something5)

compiler/testData/diagnostics/tests/syntheticExtensions/javaProperties/KotlinOverridesJava.txt

@@ -30,7 +30,7 @@ public abstract class KotlinClass : JavaClass, KotlinInterface, JavaInterface {
     public open override /*2*/ fun getSomething1(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun getSomething2(): kotlin.Int
     public open override /*1*/ fun getSomething3(): kotlin.String
-    public abstract override /*2*/ /*fake_override*/ fun getSomething4(): kotlin.String!
+    public abstract override /*2*/ /*fake_override*/ fun getSomething4(): kotlin.String
     public open override /*1*/ fun getSomething5(): kotlin.String
     public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ fun setSomething4(/*0*/ value: kotlin.String): kotlin.Unit

compiler/testData/diagnostics/testsWithJsStdLib/dynamicTypes/overrides.txt

@@ -26,7 +26,7 @@ public interface B : A {
 public interface C : A, A1 {
     public abstract override /*1*/ /*fake_override*/ fun dynamic(/*0*/ p: dynamic): dynamic
     public open override /*2*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
-    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ p: dynamic): dynamic
+    public abstract override /*2*/ /*fake_override*/ fun foo(/*0*/ p: P): R
     public open override /*2*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*2*/ /*fake_override*/ fun toString(): kotlin.String
 }