[FIR] Combine type attributes in typealias expansion

^KT-48651 Fixed

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

@@ -17,6 +17,8 @@ object CompilerConeAttributes {
 
         override fun union(other: Exact?): Exact? = null
         override fun intersect(other: Exact?): Exact? = null
+        override fun add(other: Exact?): Exact = this
+
         override fun isSubtypeOf(other: Exact?): Boolean = true
 
         override val key: KClass<out Exact> = Exact::class
@@ -29,6 +31,7 @@ object CompilerConeAttributes {
 
         override fun union(other: NoInfer?): NoInfer? = null
         override fun intersect(other: NoInfer?): NoInfer? = null
+        override fun add(other: NoInfer?): NoInfer = this
         override fun isSubtypeOf(other: NoInfer?): Boolean = true
 
         override val key: KClass<out NoInfer> = NoInfer::class
@@ -41,6 +44,8 @@ object CompilerConeAttributes {
 
         override fun union(other: EnhancedNullability?): EnhancedNullability? = other
         override fun intersect(other: EnhancedNullability?): EnhancedNullability = this
+        override fun add(other: EnhancedNullability?): EnhancedNullability = this
+
         override fun isSubtypeOf(other: EnhancedNullability?): Boolean = true
 
         override val key: KClass<out EnhancedNullability> = EnhancedNullability::class
@@ -53,6 +58,8 @@ object CompilerConeAttributes {
 
         override fun union(other: ExtensionFunctionType?): ExtensionFunctionType? = other
         override fun intersect(other: ExtensionFunctionType?): ExtensionFunctionType = this
+        override fun add(other: ExtensionFunctionType?): ExtensionFunctionType = this
+
         override fun isSubtypeOf(other: ExtensionFunctionType?): Boolean = true
 
         override val key: KClass<out ExtensionFunctionType> = ExtensionFunctionType::class
@@ -65,6 +72,8 @@ object CompilerConeAttributes {
 
         override fun union(other: UnsafeVariance?): UnsafeVariance? = null
         override fun intersect(other: UnsafeVariance?): UnsafeVariance? = null
+        override fun add(other: UnsafeVariance?): UnsafeVariance = this
+
         override fun isSubtypeOf(other: UnsafeVariance?): Boolean = true
 
         override val key: KClass<out UnsafeVariance> = UnsafeVariance::class

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

@@ -15,6 +15,17 @@ import kotlin.reflect.KClass
 abstract class ConeAttribute<T : ConeAttribute<T>> : AnnotationMarker {
     abstract fun union(other: @UnsafeVariance T?): T?
     abstract fun intersect(other: @UnsafeVariance T?): T?
+
+    /*
+     * This function is used to decide how multiple attributes should be united in presence of typealiases:
+     * typealias B = @SomeAttribute(1) A
+     * typealias C = @SomeAttribute(2) B
+     *
+     * For determining attribute value of expanded type of C we should add @SomeAttribute(2) to @SomeAttribute(1)
+     *
+     * This function must be symmetrical: a.add(b) == b.add(a)
+     */
+    abstract fun add(other: @UnsafeVariance T?): T
     abstract fun isSubtypeOf(other: @UnsafeVariance T?): Boolean
 
     abstract override fun toString(): String
@@ -65,6 +76,10 @@ class ConeAttributes private constructor(attributes: List<ConeAttribute<*>>) : A
         return perform(other) { this.intersect(it) }
     }
 
+    fun add(other: ConeAttributes): ConeAttributes {
+        return perform(other) { this.add(it) }
+    }
+
     operator fun contains(attribute: ConeAttribute<*>): Boolean {
         val index = getId(attribute.key)
         return arrayMap[index] != null