From 0de7c474959c47003abb941dc7a657d8e010b96b Mon Sep 17 00:00:00 2001
From: Jiaming Yuan <jm.yuan@outlook.com>
Date: Sat, 22 Jul 2023 08:39:21 +0800
Subject: [PATCH] Fix metric serialization. (#9405)

---
 src/learner.cc            |  8 ++++----
 tests/cpp/test_learner.cc | 28 ++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/src/learner.cc b/src/learner.cc
index 2f453ea30..b2d6baff0 100644
--- a/src/learner.cc
+++ b/src/learner.cc
@@ -583,8 +583,9 @@ class LearnerConfiguration : public Learner {
     auto& objective_fn = learner_parameters["objective"];
     obj_->SaveConfig(&objective_fn);
 
-    std::vector<Json> metrics(metrics_.size(), Json{Object{}});
+    std::vector<Json> metrics(metrics_.size());
     for (size_t i = 0; i < metrics_.size(); ++i) {
+      metrics[i] = Object{};
       metrics_[i]->SaveConfig(&metrics[i]);
     }
     learner_parameters["metrics"] = Array(std::move(metrics));
@@ -807,14 +808,13 @@ class LearnerConfiguration : public Learner {
 
   void ConfigureMetrics(Args const& args) {
     for (auto const& name : metric_names_) {
-      auto DupCheck = [&name](std::unique_ptr<Metric> const& m) {
-                        return m->Name() != name;
-                      };
+      auto DupCheck = [&name](std::unique_ptr<Metric> const& m) { return m->Name() != name; };
       if (std::all_of(metrics_.begin(), metrics_.end(), DupCheck)) {
         metrics_.emplace_back(std::unique_ptr<Metric>(Metric::Create(name, &ctx_)));
         mparam_.contain_eval_metrics = 1;
       }
     }
+
     for (auto& p_metric : metrics_) {
       p_metric->Configure(args);
     }
diff --git a/tests/cpp/test_learner.cc b/tests/cpp/test_learner.cc
index 2165c6c8d..3615f7587 100644
--- a/tests/cpp/test_learner.cc
+++ b/tests/cpp/test_learner.cc
@@ -215,6 +215,34 @@ TEST(Learner, JsonModelIO) {
   }
 }
 
+TEST(Learner, ConfigIO) {
+  bst_row_t n_samples = 128;
+  bst_feature_t n_features = 12;
+  std::shared_ptr<DMatrix> p_fmat{
+      RandomDataGenerator{n_samples, n_features, 0}.GenerateDMatrix(true, false, 2)};
+
+  auto serialised_model_tmp = std::string{};
+  std::string eval_res_0;
+  std::string eval_res_1;
+  {
+    std::unique_ptr<Learner> learner{Learner::Create({p_fmat})};
+    learner->SetParams(Args{{"eval_metric", "ndcg"}, {"eval_metric", "map"}});
+    learner->Configure();
+    learner->UpdateOneIter(0, p_fmat);
+    eval_res_0 = learner->EvalOneIter(0, {p_fmat}, {"Train"});
+    common::MemoryBufferStream fo(&serialised_model_tmp);
+    learner->Save(&fo);
+  }
+
+  {
+    common::MemoryBufferStream fi(&serialised_model_tmp);
+    std::unique_ptr<Learner> learner{Learner::Create({p_fmat})};
+    learner->Load(&fi);
+    eval_res_1 = learner->EvalOneIter(0, {p_fmat}, {"Train"});
+  }
+  ASSERT_EQ(eval_res_0, eval_res_1);
+}
+
 // Crashes the test runner if there are race condiditions.
 //
 // Build with additional cmake flags to enable thread sanitizer