FIR2IR: don't mutate basic FIR for invoke / next calls

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -889,28 +889,27 @@ class Fir2IrVisitor(
         val convertibleCall = if (functionCall.toResolvedCallableSymbol()?.fir is FirIntegerOperator) {
             functionCall.copy().transformSingle(integerApproximator, null)
         } else {
-            checkIfInvoke(functionCall)
+            functionCall.replaceCalleeReferenceWithOverridden()
         }
         return convertibleCall.toIrExpression(convertibleCall.typeRef)
             .applyCallArguments(convertibleCall).applyTypeArguments(convertibleCall).applyReceivers(convertibleCall)
     }
 
-    // Use the generic invoke method in Function classes, to match bridges generated by the backend.
-    private fun checkIfInvoke(functionCall: FirFunctionCall): FirFunctionCall {
-        if (functionCall !is FirFunctionCallImpl) {
-            return functionCall
-        }
-        val calleeReference = (functionCall.calleeReference as? FirResolvedNamedReference) ?: return functionCall
-        val resolvedSymbol = (calleeReference.resolvedSymbol as? FirNamedFunctionSymbol) ?: return functionCall
+    // Use the generic invoke & next methods to match bridges generated by the backend.
+    private fun FirFunctionCall.replaceCalleeReferenceWithOverridden(): FirFunctionCall {
+        val calleeReference = (calleeReference as? FirResolvedNamedReference) ?: return this
+        val resolvedSymbol = (calleeReference.resolvedSymbol as? FirNamedFunctionSymbol) ?: return this
+        val overriddenSymbol = resolvedSymbol.overriddenSymbol ?: return this
         if (resolvedSymbol.callableId.isInvoke() || resolvedSymbol.callableId.isIteratorNext()) {
-            functionCall.calleeReference =
-                buildResolvedNamedReference {
+            return copy(
+                calleeReference = buildResolvedNamedReference {
                     source = calleeReference.source
                     name = calleeReference.name
-                    this.resolvedSymbol = resolvedSymbol.overriddenSymbol!!
+                    this.resolvedSymbol = overriddenSymbol
                 }
+            )
         }
-        return functionCall
+        return this
     }
 
     override fun visitAnnotationCall(annotationCall: FirAnnotationCall, data: Any?): IrElement {