[FIR] Add extension with additional checkers

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/CheckersComponent.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.FirSessionComponent
 import org.jetbrains.kotlin.fir.analysis.checkers.declaration.*
 import org.jetbrains.kotlin.fir.analysis.checkers.expression.*
+import org.jetbrains.kotlin.fir.analysis.extensions.FirAdditionalCheckersExtension
 
 class CheckersComponent : FirSessionComponent {
     companion object {
@@ -33,6 +34,11 @@ class CheckersComponent : FirSessionComponent {
     fun register(checkers: ExpressionCheckers) {
         _expressionCheckers.register(checkers)
     }
+
+    fun register(checkers: FirAdditionalCheckersExtension) {
+        register(checkers.declarationCheckers)
+        register(checkers.expressionCheckers)
+    }
 }
 
 val FirSession.checkersComponent: CheckersComponent by FirSession.sessionComponentAccessor()

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/collectors/FirDiagnosticsCollector.kt

@@ -6,9 +6,13 @@
 package org.jetbrains.kotlin.fir.analysis.collectors
 
 import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.analysis.checkersComponent
+import org.jetbrains.kotlin.fir.analysis.extensions.additionalCheckers
+import org.jetbrains.kotlin.fir.extensions.extensionsService
 
 object FirDiagnosticsCollector {
     fun create(session: FirSession): AbstractDiagnosticCollector {
+        session.registerAdditionalCheckers()
         val collector = SimpleDiagnosticsCollector(session)
         collector.registerAllComponents()
         return collector
@@ -17,8 +21,13 @@ object FirDiagnosticsCollector {
     // Use in CLI compiler
     @Suppress("unused")
     fun createParallel(session: FirSession): AbstractDiagnosticCollector {
+        session.registerAdditionalCheckers()
         val collector = ParallelDiagnosticsCollector(session, numberOfThreads = 4)
         collector.registerAllComponents()
         return collector
     }
+
+    private fun FirSession.registerAdditionalCheckers() {
+        extensionsService.additionalCheckers.forEach(checkersComponent::register)
+    }
 }

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/extensions/FirAdditionalCheckersExtension.kt

@@ -0,0 +1,52 @@
+/*
+ * 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.analysis.extensions
+
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.analysis.checkers.declaration.DeclarationCheckers
+import org.jetbrains.kotlin.fir.analysis.checkers.expression.ExpressionCheckers
+import org.jetbrains.kotlin.fir.extensions.*
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KProperty
+
+abstract class FirAdditionalCheckersExtension(session: FirSession) : AbstractFirAdditionalCheckersExtension(session) {
+    companion object {
+        val NAME = FirExtensionPointName("ExtensionCheckers")
+    }
+
+    open val declarationCheckers: DeclarationCheckers = DeclarationCheckers.EMPTY
+    open val expressionCheckers: ExpressionCheckers = ExpressionCheckers.EMPTY
+
+    final override val name: FirExtensionPointName
+        get() = NAME
+
+    final override val directlyApplicableAnnotations: Set<AnnotationFqn>
+        get() = emptySet()
+
+    final override val childrenApplicableAnnotations: Set<AnnotationFqn>
+        get() = emptySet()
+
+    final override val metaAnnotations: Map<AnnotationFqn, MetaAnnotationMode>
+        get() = emptyMap()
+
+    final override val mode: Mode
+        get() = Mode.ALL
+}
+
+val FirExtensionsService.additionalCheckers: List<FirAdditionalCheckersExtension> by FirExtensionsService.additionalCheckers()
+
+private fun FirExtensionsService.Companion.additionalCheckers(): ReadOnlyProperty<FirExtensionsService, List<FirAdditionalCheckersExtension>> {
+    val accessor = generateAccessor<FirRegisteredExtension<AbstractFirAdditionalCheckersExtension>, AbstractFirAdditionalCheckersExtension>(
+        AbstractFirAdditionalCheckersExtension::class
+    )
+    return object : ReadOnlyProperty<FirExtensionsService, List<FirAdditionalCheckersExtension>> {
+        override fun getValue(thisRef: FirExtensionsService, property: KProperty<*>): List<FirAdditionalCheckersExtension> {
+            val extensions = accessor.getValue(thisRef, property)
+            @Suppress("UNCHECKED_CAST")
+            return extensions.extensionsWithAllMode as List<FirAdditionalCheckersExtension>
+        }
+    }
+}