IrConstTransformer: handle vararg with spread elements properly

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/evaluate/IrConstTransformer.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.expressions.impl.IrVarargImpl
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 
@@ -60,18 +61,28 @@ class IrConstTransformer(irBuiltIns: IrBuiltIns) : IrElementTransformerVoid() {
             for (i in 0 until annotation.valueArgumentsCount) {
                 val arg = annotation.getValueArgument(i) ?: continue
                 when (arg) {
-                    is IrVararg -> arg.transformVarArg()
+                    is IrVararg -> annotation.putValueArgument(i, arg.transformVarArg())
                     else -> annotation.putValueArgument(i, arg.transformSingleArg(annotation.symbol.owner.valueParameters[i].type))
                 }
             }
         }
     }
 
-    private fun IrVararg.transformVarArg() {
-        for (i in this.elements.indices) {
-            val irVarargElement = this.elements[i] as? IrExpression ?: continue
-            this.putElement(i, irVarargElement.transformSingleArg(this.varargElementType))
+    private fun IrVararg.transformVarArg(): IrVararg {
+        if (elements.isEmpty()) return this
+        val newIrVararg = IrVarargImpl(this.startOffset, this.endOffset, this.type, this.varargElementType)
+        for (element in this.elements) {
+            when (element) {
+                is IrExpression -> newIrVararg.addElement(element.transformSingleArg(this.varargElementType))
+                is IrSpreadElement -> {
+                    when (val expression = element.expression) {
+                        is IrVararg -> expression.transformVarArg().elements.forEach { newIrVararg.addElement(it) }
+                        else -> newIrVararg.addElement(expression.transformSingleArg(this.varargElementType))
+                    }
+                }
+            }
         }
+        return newIrVararg
     }
 
     private fun IrExpression.transformSingleArg(expectedType: IrType): IrExpression {

compiler/testData/codegen/box/collectionLiterals/collectionLiteralsWithVarargs.kt

@@ -1,5 +1,4 @@
 // WITH_REFLECT
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM
 
 import java.util.Arrays

compiler/testData/ir/irText/declarations/annotations/spreadOperatorInAnnotationArguments.fir.txt

@@ -29,5 +29,5 @@ FILE fqName:<root> fileName:/spreadOperatorInAnnotationArguments.kt
       $this: VALUE_PARAMETER name:<this> type:kotlin.Any
   FUN name:test visibility:public modality:FINAL <> () returnType:kotlin.Unit
     annotations:
-      A(xs = [SPREAD_ELEMENT, SPREAD_ELEMENT])
+      A(xs = ['a', 'b'])
     BLOCK_BODY