FIR: support custom annotation-based type attributes

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

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.types
+
+import org.jetbrains.kotlin.fir.expressions.FirAnnotationCall
+import org.jetbrains.kotlin.fir.render
+import kotlin.reflect.KClass
+
+class CustomAnnotationTypeAttribute(val annotations: List<FirAnnotationCall>) : ConeAttribute<CustomAnnotationTypeAttribute>() {
+    override fun union(other: CustomAnnotationTypeAttribute?): CustomAnnotationTypeAttribute? = null
+
+    override fun intersect(other: CustomAnnotationTypeAttribute?): CustomAnnotationTypeAttribute? = null
+
+    override fun isSubtypeOf(other: CustomAnnotationTypeAttribute?): Boolean = true
+
+    override fun toString(): String = annotations.joinToString(separator = " ") { it.render() }
+
+    override val key: KClass<out CustomAnnotationTypeAttribute>
+        get() = CustomAnnotationTypeAttribute::class
+}
+
+private val ConeAttributes.custom: CustomAnnotationTypeAttribute? by ConeAttributes.attributeAccessor<CustomAnnotationTypeAttribute>()
+
+val ConeAttributes.customAnnotations: List<FirAnnotationCall> get() = custom?.annotations.orEmpty()

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

@@ -95,6 +95,7 @@ fun List<FirAnnotationCall>.computeTypeAttributes(
 ): ConeAttributes {
     if (this.isEmpty()) return ConeAttributes.Empty
     val attributes = mutableListOf<ConeAttribute<*>>()
+    val customAnnotations = mutableListOf<FirAnnotationCall>()
     for (annotation in this) {
         val type = annotation.annotationTypeRef.coneTypeSafe<ConeClassLikeType>() ?: continue
         when (val classId = type.lookupTag.classId) {
@@ -102,9 +103,18 @@ fun List<FirAnnotationCall>.computeTypeAttributes(
             CompilerConeAttributes.NoInfer.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.NoInfer
             CompilerConeAttributes.ExtensionFunctionType.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.ExtensionFunctionType
             CompilerConeAttributes.UnsafeVariance.ANNOTATION_CLASS_ID -> attributes += CompilerConeAttributes.UnsafeVariance
-            else -> additionalProcessor.invoke(attributes, classId)
+            else -> {
+                if (classId.startsWith(StandardClassIds.BASE_KOTLIN_PACKAGE.shortName())) {
+                    // The check ^ is intended to leave only annotations which may be important for BE
+                    customAnnotations += annotation
+                }
+                additionalProcessor.invoke(attributes, classId)
+            }
         }
     }
+    if (customAnnotations.isNotEmpty()) {
+        attributes += CustomAnnotationTypeAttribute(customAnnotations)
+    }
     return ConeAttributes.create(attributes)
 }