From fc559ab0cd1fa275c30923c4bdb5b1d33ccb3488 Mon Sep 17 00:00:00 2001
From: Ilya Goncharov <ilya.goncharov@jetbrains.com>
Date: Tue, 2 Mar 2021 16:16:52 +0300
Subject: [PATCH] [JS IR] Unite varargs and non varargs before vararg

---
 .../backend/js/transformers/irToJs/jsAstUtils.kt  | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/jsAstUtils.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/jsAstUtils.kt
index f7c100e0aa1..f421d6d4cdf 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/jsAstUtils.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/jsAstUtils.kt
@@ -258,8 +258,21 @@ fun argumentsWithVarargAsSingleArray(
         concatElements.add(JsArrayLiteral(arraysForConcat))
     }
 
+    if (concatElements.isEmpty()) {
+        return JsArrayLiteral()
+    }
+
+    if (concatElements.all { it is JsArrayLiteral }) {
+        return concatElements
+            .fold(mutableListOf<JsExpression>()) { aggregatedArrayExpressions, arrayLiteral ->
+                arrayLiteral as JsArrayLiteral
+                aggregatedArrayExpressions.addAll(arrayLiteral.expressions)
+                aggregatedArrayExpressions
+            }
+            .let { JsArrayLiteral(it) }
+    }
+
     return when (concatElements.size) {
-        0 -> JsArrayLiteral()
         1 -> concatElements[0]
         else -> JsInvocation(
             JsNameRef("concat", concatElements.first()),