From 28598a211168f5f740fcb35bf84e4e336b86bb32 Mon Sep 17 00:00:00 2001
From: Laurent Perron <lperron@google.com>
Date: Fri, 4 Apr 2025 17:05:22 +0200
Subject: [PATCH] use arena in flatzinc

---
 ortools/flatzinc/cp_model_fz_solver.cc | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/ortools/flatzinc/cp_model_fz_solver.cc b/ortools/flatzinc/cp_model_fz_solver.cc
index 93f322c051..874cf5c788 100644
--- a/ortools/flatzinc/cp_model_fz_solver.cc
+++ b/ortools/flatzinc/cp_model_fz_solver.cc
@@ -17,6 +17,7 @@
 #include <cstdint>
 #include <functional>
 #include <limits>
+#include <memory>
 #include <string>
 #include <tuple>
 #include <utility>
@@ -30,6 +31,7 @@
 #include "absl/strings/match.h"
 #include "absl/strings/str_cat.h"
 #include "absl/types/span.h"
+#include "google/protobuf/arena.h"
 #include "google/protobuf/text_format.h"
 #include "ortools/base/iterator_adaptors.h"
 #include "ortools/flatzinc/checker.h"
@@ -64,6 +66,10 @@ int FalseLiteral(int var) { return -var - 1; }
 
 // Helper class to convert a flatzinc model to a CpModelProto.
 struct CpModelProtoWithMapping {
+  CpModelProtoWithMapping()
+      : arena(std::make_unique<google::protobuf::Arena>()),
+        proto(*google::protobuf::Arena::Create<CpModelProto>(arena.get())) {}
+
   // Returns a constant CpModelProto variable created on-demand.
   int LookupConstant(int64_t value);
 
@@ -135,7 +141,8 @@ struct CpModelProtoWithMapping {
       SolverLogger* logger);
 
   // The output proto.
-  CpModelProto proto;
+  std::unique_ptr<google::protobuf::Arena> arena;
+  CpModelProto& proto;
   SatParameters parameters;
 
   // Mapping from flatzinc variables to CpModelProto variables.