Introduce UnsafeVariance annotation

core/builtins/src/kotlin/Annotations.kt

@@ -119,6 +119,14 @@ public annotation class HiddenDeclaration
 @MustBeDocumented
 private annotation class external
 
+/**
+ * Suppresses errors about variance conflict
+ */
+@Target(TYPE)
+@Retention(SOURCE)
+@MustBeDocumented
+public annotation class UnsafeVariance
+
 /**
  * Specifies that the corresponding type should be ignored during type inference.
  */

core/descriptors/src/org/jetbrains/kotlin/builtins/KotlinBuiltIns.java

@@ -151,6 +151,7 @@ public abstract class KotlinBuiltIns {
         public final FqName retention = annotationName("Retention");
         public final FqName repeatable = annotationName("Repeatable");
         public final FqName mustBeDocumented = annotationName("MustBeDocumented");
+        public final FqName unsafeVariance = fqName("UnsafeVariance");
 
         public final FqName mutableList = fqName("MutableList");
         public final FqName mutableSet = fqName("MutableSet");

core/descriptors/src/org/jetbrains/kotlin/descriptors/annotations/Annotations.kt

@@ -26,6 +26,8 @@ public interface Annotations : Iterable<AnnotationDescriptor> {
 
     public fun findAnnotation(fqName: FqName): AnnotationDescriptor?
 
+    public fun hasAnnotation(fqName: FqName) = findAnnotation(fqName) != null
+
     public fun findExternalAnnotation(fqName: FqName): AnnotationDescriptor?
 
     public fun getUseSiteTargetedAnnotations(): List<AnnotationWithTarget>