[FIR] Introduce UnsafeVariance attribute (see KT-41792)

compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/CompilerConeAttributes.kt

@@ -8,7 +8,6 @@ package org.jetbrains.kotlin.fir.types
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.utils.addToStdlib.runIf
 import kotlin.reflect.KClass
 
 object CompilerConeAttributes {
@@ -41,8 +40,19 @@ object CompilerConeAttributes {
 
         override val key: KClass<out ExtensionFunctionType> = ExtensionFunctionType::class
     }
+
+    object UnsafeVariance : ConeAttribute<UnsafeVariance>() {
+        val ANNOTATION_CLASS_ID = ClassId(FqName("kotlin"), Name.identifier("UnsafeVariance"))
+
+        override fun union(other: UnsafeVariance?): UnsafeVariance? = null
+        override fun intersect(other: UnsafeVariance?): UnsafeVariance? = null
+        override fun isSubtypeOf(other: UnsafeVariance?): Boolean = true
+
+        override val key: KClass<out UnsafeVariance> = UnsafeVariance::class
+    }
 }
 
 val ConeAttributes.exact: CompilerConeAttributes.Exact? by ConeAttributes.attributeAccessor<CompilerConeAttributes.Exact>()
 val ConeAttributes.noInfer: CompilerConeAttributes.NoInfer? by ConeAttributes.attributeAccessor<CompilerConeAttributes.NoInfer>()
 val ConeAttributes.extensionFunctionType: CompilerConeAttributes.ExtensionFunctionType? by ConeAttributes.attributeAccessor<CompilerConeAttributes.ExtensionFunctionType>()
+val ConeAttributes.unsafeVarianceType: CompilerConeAttributes.UnsafeVariance? by ConeAttributes.attributeAccessor<CompilerConeAttributes.UnsafeVariance>()

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/TypeUtils.kt

@@ -161,3 +161,13 @@ fun ConeKotlinType.isExtensionFunctionType(session: FirSession): Boolean {
 fun FirTypeRef.isExtensionFunctionType(session: FirSession): Boolean {
     return coneTypeSafe<ConeKotlinType>()?.isExtensionFunctionType(session) == true
 }
+
+fun ConeKotlinType.isUnsafeVarianceType(session: FirSession): Boolean {
+    val type = this.lowerBoundIfFlexible().fullyExpandedType(session)
+    return type.attributes.unsafeVarianceType != null
+}
+
+fun FirTypeRef.isUnsafeVarianceType(session: FirSession): Boolean {
+    return coneTypeSafe<ConeKotlinType>()?.isUnsafeVarianceType(session) == true
+}
+

compiler/fir/tree/src/org/jetbrains/kotlin/fir/types/FirTypeUtils.kt

@@ -96,6 +96,7 @@ fun List<FirAnnotationCall>.computeTypeAttributes(): ConeAttributes {
             CompilerConeAttributes.Exact.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.Exact
             CompilerConeAttributes.NoInfer.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.NoInfer
             CompilerConeAttributes.ExtensionFunctionType.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.ExtensionFunctionType
+            CompilerConeAttributes.UnsafeVariance.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.UnsafeVariance
         }
     }
     return ConeAttributes.create(attributes)