[FIR] Add service for fir extension points

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/extensions/FirRegisteredExtension.kt

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2010-2020 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.extensions
+
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.FirSessionComponent
+import org.jetbrains.kotlin.fir.utils.ComponentArrayOwner
+import org.jetbrains.kotlin.fir.utils.ComponentTypeRegistry
+import org.jetbrains.kotlin.name.Name
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KClass
+import kotlin.reflect.KProperty
+
+abstract class FirExtensionPoint(val session: FirSession) {
+    abstract val name: FirExtensionPointName
+
+    fun interface Factory<P : FirExtensionPoint> {
+        fun create(session: FirSession): P
+    }
+}
+
+data class FirExtensionPointName(val name: Name) {
+    constructor(name: String) : this(Name.identifier(name))
+}
+
+@Suppress("EXPERIMENTAL_FEATURE_WARNING")
+inline class FirRegisteredExtension<P : FirExtensionPoint>(val extensions: List<P>)
+
+class FirExtensionPointService(
+    private val session: FirSession
+) : ComponentArrayOwner<FirExtensionPoint, FirRegisteredExtension<*>>(), FirSessionComponent {
+    companion object : ComponentTypeRegistry<FirExtensionPoint, FirRegisteredExtension<*>>() {
+        inline fun <reified K : FirExtensionPoint, V : FirRegisteredExtension<K>> registeredExtensions(): ReadOnlyProperty<FirExtensionPointService, List<K>> {
+            val accessor = generateAccessor<V, K>(K::class)
+            return object : ReadOnlyProperty<FirExtensionPointService, List<K>> {
+                override fun getValue(thisRef: FirExtensionPointService, property: KProperty<*>): List<K> {
+                    return accessor.getValue(thisRef, property).extensions
+                }
+            }
+        }
+    }
+
+    override val typeRegistry: ComponentTypeRegistry<FirExtensionPoint, FirRegisteredExtension<*>>
+        get() = Companion
+
+    fun <P : FirExtensionPoint> registerExtensions(extensionClass: KClass<P>, extensions: List<FirExtensionPoint.Factory<P>>) {
+        registerComponent(extensionClass, FirRegisteredExtension(extensions.map { it.create(session) }))
+    }
+}
+
+val FirSession.extensionPointService: FirExtensionPointService by FirSession.sessionComponentAccessor()