[FIR/IR generator] Deduplicate interface/abstract class configuration

generators/tree-generator-common/build.gradle.kts

@@ -5,6 +5,8 @@ plugins {
 
 dependencies {
     api(project(":core:compiler.common"))
+
+    implementation(project(":generators"))
 }
 
 sourceSets {

generators/tree-generator-common/src/org/jetbrains/kotlin/generators/tree/InterfaceAndAbstractClassConfigurator.kt

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2010-2023 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.generators.tree
+
+import org.jetbrains.kotlin.generators.util.Node
+import org.jetbrains.kotlin.generators.util.solveGraphForClassVsInterface
+
+/**
+ * Decides which element in the tree must be an (abstract) class, and which must be an interface.
+ */
+abstract class InterfaceAndAbstractClassConfigurator {
+
+    private inner class NodeImpl(val element: ImplementationKindOwner) : Node {
+        override val parents: List<NodeImpl>
+            get() = element.allParents.map(::NodeImpl)
+
+        override val origin: NodeImpl
+            get() = if (element.origin == element) this else NodeImpl(element.origin)
+
+        override fun equals(other: Any?): Boolean = other is NodeImpl && element == other.element
+
+        override fun hashCode(): Int = element.hashCode()
+    }
+
+    protected open val ImplementationKindOwner.origin: ImplementationKindOwner
+        get() = this
+
+    /**
+     * The list of elements of the tree to infer their [ImplementationKind].
+     */
+    protected abstract val elements: List<ImplementationKindOwner>
+
+    /**
+     * If [element]'s kind was inferred as abstract class, allows to forcibly make that element a final class instead.
+     */
+    protected open fun shouldBeFinalClass(element: ImplementationKindOwner, allParents: Set<ImplementationKindOwner>): Boolean = false
+
+    private fun updateKinds(nodes: List<NodeImpl>, solution: List<Boolean>) {
+        val allParents = nodes.flatMapTo(mutableSetOf()) { element -> element.parents.map { it.origin.element } }
+
+        for (index in solution.indices) {
+            val isClass = solution[index]
+            val node = nodes[index].origin
+            val element = node.element
+            val existingKind = element.kind
+            if (isClass) {
+                require(existingKind != ImplementationKind.Interface) {
+                    "$element must NOT be an interface"
+                }
+                if (existingKind == null) {
+                    element.kind = if (shouldBeFinalClass(element, allParents))
+                        ImplementationKind.FinalClass
+                    else
+                        ImplementationKind.AbstractClass
+                }
+            } else {
+                element.kind = ImplementationKind.Interface
+            }
+        }
+    }
+
+    private fun updateSealedKinds(nodes: Collection<NodeImpl>) {
+        for (node in nodes) {
+            val element = node.element
+            if (element is AbstractElement<*, *>) {
+                if (element.isSealed) {
+                    element.kind = when (element.kind) {
+                        ImplementationKind.AbstractClass -> ImplementationKind.SealedClass
+                        ImplementationKind.Interface -> ImplementationKind.SealedInterface
+                        else -> error("element $element with kind ${element.kind} can not be sealed")
+                    }
+                }
+            }
+        }
+    }
+
+    fun configureInterfacesAndAbstractClasses() {
+        val nodes = this.elements.map(::NodeImpl)
+        val solution = solveGraphForClassVsInterface(
+            nodes,
+            nodes.filter { it.element.kind?.typeKind == TypeKind.Interface },
+            nodes.filter { it.element.kind?.typeKind == TypeKind.Class },
+        )
+        updateKinds(nodes, solution)
+        updateSealedKinds(nodes)
+    }
+}