Introduce FirModifierList

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirModifierList.kt

@@ -0,0 +1,38 @@
+/*
+ * 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
+
+import com.intellij.lang.ASTNode
+import com.intellij.lang.LighterASTNode
+import com.intellij.psi.tree.TokenSet
+import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
+import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.psi.KtModifierList
+
+sealed class FirModifierList {
+    abstract val modifiers: List<FirModifier<*>>
+}
+
+private val MODIFIER_KEYWORD_SET = TokenSet.orSet(KtTokens.SOFT_KEYWORDS, TokenSet.create(KtTokens.IN_KEYWORD, KtTokens.FUN_KEYWORD))
+
+class FirPsiModifierList(val modifierList: KtModifierList) : FirModifierList() {
+    override val modifiers: List<FirPsiModifier>
+        get() = modifierList.node.getChildren(MODIFIER_KEYWORD_SET).map { node ->
+            FirPsiModifier(node, node.elementType as KtModifierKeywordToken)
+        }
+
+}
+
+class FirLightModifierList(val modifierList: LighterASTNode) : FirModifierList() {
+    override val modifiers: List<FirLightModifier>
+        get() = TODO()
+}
+
+sealed class FirModifier<Node : Any>(val node: Node, val token: KtModifierKeywordToken)
+
+class FirPsiModifier(node: ASTNode, token: KtModifierKeywordToken) : FirModifier<ASTNode>(node, token)
+
+class FirLightModifier(node: LighterASTNode, token: KtModifierKeywordToken) : FirModifier<LighterASTNode>(node, token)

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirSourceElement.kt

@@ -7,8 +7,10 @@ package org.jetbrains.kotlin.fir
 
 import com.intellij.lang.LighterASTNode
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
+import org.jetbrains.kotlin.psi.KtModifierListOwner
 
-abstract class FirSourceElement
+sealed class FirSourceElement
 
 class FirPsiSourceElement(val psi: PsiElement) : FirSourceElement()
 class FirLightSourceElement(val element: LighterASTNode) : FirSourceElement()
@@ -24,3 +26,11 @@ inline fun PsiElement.toFirSourceElement(): FirPsiSourceElement = FirPsiSourceEl
 inline fun LighterASTNode.toFirSourceElement(): FirLightSourceElement = FirLightSourceElement(this)
 
 val FirSourceElement?.lightNode: LighterASTNode? get() = (this as? FirLightSourceElement)?.element
+
+fun FirSourceElement?.getModifierList(): FirModifierList? {
+    return when (this) {
+        is FirPsiSourceElement -> (psi as? KtModifierListOwner)?.modifierList?.let { FirPsiModifierList(it) }
+        is FirLightSourceElement -> FirLightModifierList(element)
+        null -> null
+    }
+}