KT-1934 & KT-10197:

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

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
+}