From d2bc0f0f08d2b9e1040cc440dfce1a88281ff7c3 Mon Sep 17 00:00:00 2001
From: Philip Hyunsu Cho <chohyu01@cs.washington.edu>
Date: Fri, 6 May 2022 22:49:38 -0700
Subject: [PATCH] Allow loading old models from RDS (#7864)

---
 .../tests/testthat/test_model_compatibility.R  | 17 ++++++++---------
 src/learner.cc                                 |  8 +++++++-
 src/tree/updater_quantile_hist.h               | 18 +-----------------
 3 files changed, 16 insertions(+), 27 deletions(-)

diff --git a/R-package/tests/testthat/test_model_compatibility.R b/R-package/tests/testthat/test_model_compatibility.R
index 0f13bdc73..6a35ca4b3 100644
--- a/R-package/tests/testthat/test_model_compatibility.R
+++ b/R-package/tests/testthat/test_model_compatibility.R
@@ -77,6 +77,7 @@ test_that("Models from previous versions of XGBoost can be loaded", {
     model_xgb_ver <- m[2]
     name <- m[3]
     is_rds <- endsWith(model_file, '.rds')
+    is_json <- endsWith(model_file, '.json')
 
     cpp_warning <- capture.output({
       # Expect an R warning when a model is loaded from RDS and it was generated by version < 1.1.x
@@ -95,15 +96,13 @@ test_that("Models from previous versions of XGBoost can be loaded", {
         run_booster_check(booster, name)
       }
     })
-    if (compareVersion(model_xgb_ver, '1.0.0.0') < 0) {
-      # Expect a C++ warning when a model was generated in version < 1.0.x
-      m <- grepl(paste0('.*Loading model from XGBoost < 1\\.0\\.0, consider saving it again for ',
-                        'improved compatibility.*'), cpp_warning, perl = TRUE)
-      expect_true(length(m) > 0 && all(m))
-    } else if (is_rds && model_xgb_ver == '1.1.1.1') {
-      # Expect a C++ warning when a model is loaded from RDS and it was generated by version 1.1.x
-      m <- grepl(paste0('.*Attempted to load internal configuration for a model file that was ',
-                        'generated by a previous version of XGBoost.*'), cpp_warning, perl = TRUE)
+    cpp_warning <- paste0(cpp_warning, collapse = ' ')
+    if (is_rds && compareVersion(model_xgb_ver, '1.1.1.1') >= 0) {
+      # Expect a C++ warning when a model is loaded from RDS and it was generated by old XGBoost`
+      m <- grepl(paste0('.*If you are loading a serialized model ',
+                        '\\(like pickle in Python, RDS in R\\).*',
+                        'for more details about differences between ',
+                        'saving model and serializing.*'), cpp_warning, perl = TRUE)
       expect_true(length(m) > 0 && all(m))
     }
   })
diff --git a/src/learner.cc b/src/learner.cc
index 20b342b7b..568cfc680 100644
--- a/src/learner.cc
+++ b/src/learner.cc
@@ -406,8 +406,14 @@ class LearnerConfiguration : public Learner {
   }
 
   void LoadConfig(Json const& in) override {
+    // If configuration is loaded, ensure that the model came from the same version
     CHECK(IsA<Object>(in));
-    Version::Load(in);
+    auto origin_version = Version::Load(in);
+
+    if (!Version::Same(origin_version)) {
+      LOG(WARNING) << ModelMsg();
+      return;  // skip configuration if version is not matched
+    }
 
     auto const& learner_parameters = get<Object>(in["learner"]);
     FromJson(learner_parameters.at("learner_train_param"), &tparam_);
diff --git a/src/tree/updater_quantile_hist.h b/src/tree/updater_quantile_hist.h
index a0cf4906e..18b4d6682 100644
--- a/src/tree/updater_quantile_hist.h
+++ b/src/tree/updater_quantile_hist.h
@@ -249,23 +249,7 @@ class QuantileHistMaker: public TreeUpdater {
   void LoadConfig(Json const& in) override {
     auto const& config = get<Object const>(in);
     FromJson(config.at("train_param"), &this->param_);
-    try {
-      FromJson(config.at("cpu_hist_train_param"), &this->hist_maker_param_);
-    } catch (std::out_of_range&) {
-      // XGBoost model is from 1.1.x, so 'cpu_hist_train_param' is missing.
-      // We add this compatibility check because it's just recently that we (developers) began
-      // persuade R users away from using saveRDS() for model serialization. Hopefully, one day,
-      // everyone will be using xgb.save().
-      LOG(WARNING)
-        << "Attempted to load internal configuration for a model file that was generated "
-        << "by a previous version of XGBoost. A likely cause for this warning is that the model "
-        << "was saved with saveRDS() in R or pickle.dump() in Python. We strongly ADVISE AGAINST "
-        << "using saveRDS() or pickle.dump() so that the model remains accessible in current and "
-        << "upcoming XGBoost releases. Please use xgb.save() instead to preserve models for the "
-        << "long term. For more details and explanation, see "
-        << "https://xgboost.readthedocs.io/en/latest/tutorials/saving_model.html";
-      this->hist_maker_param_.UpdateAllowUnknown(Args{});
-    }
+    FromJson(config.at("cpu_hist_train_param"), &this->hist_maker_param_);
   }
   void SaveConfig(Json* p_out) const override {
     auto& out = *p_out;