Prohibit nested intersection types in return position

#KT-11490 Fixed

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

@@ -35,6 +35,7 @@ import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.SubstitutionUtils
 import org.jetbrains.kotlin.types.TypeUtils
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
+import org.jetbrains.kotlin.types.typeUtil.contains
 import org.jetbrains.kotlin.types.typeUtil.isNothing
 import java.util.*
 
@@ -707,7 +708,7 @@ class DeclarationsChecker(
                             (if (declaration is KtProperty) IMPLICIT_NOTHING_PROPERTY_TYPE else IMPLICIT_NOTHING_RETURN_TYPE).on(target)
                     )
                 }
-                if (it.constructor is IntersectionTypeConstructor) {
+                if (it.contains { type -> type.constructor is IntersectionTypeConstructor }) {
                     trace.report(IMPLICIT_INTERSECTION_TYPE.on(target, it))
                 }
             }

compiler/testData/diagnostics/tests/implicitNestedIntersection.kt

@@ -0,0 +1,9 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+interface In<in E>
+open class A : In<A>
+open class B : In<B>
+
+fun <T> select(x: T, y: T) = x
+
+fun <!IMPLICIT_INTERSECTION_TYPE!>foo2<!>() = select(A(), B()) // Type is In<A & B> is prohibited in return position

compiler/testData/diagnostics/tests/implicitNestedIntersection.txt

@@ -0,0 +1,24 @@
+package
+
+public fun foo2(): In<{A & B}>
+public fun </*0*/ T> select(/*0*/ x: T, /*1*/ y: T): T
+
+public open class A : In<A> {
+    public constructor 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
+}
+
+public open class B : In<B> {
+    public constructor B()
+    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 In</*0*/ in E> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

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

@@ -301,6 +301,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
             doTest(fileName);
         }
 
+        @TestMetadata("implicitNestedIntersection.kt")
+        public void testImplicitNestedIntersection() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/implicitNestedIntersection.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("implicitNothing.kt")
         public void testImplicitNothing() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/implicitNothing.kt");