Add a test to prepare for integer default_left

src/frontend/xgboost/xgboost_json.h

@@ -349,14 +349,18 @@ class RootHandler : public OutputHandler<std::unique_ptr<treelite::Model>> {
 class DelegatedHandler
     : public rapidjson::BaseReaderHandler<rapidjson::UTF8<>, DelegatedHandler>,
       public Delegator {
-
  public:
-  /*! \brief create DelegatedHandler with initial RootHandler on stack */
-  static std::shared_ptr<DelegatedHandler> create() {
+  /*! \brief create DelegatedHandler with empty stack */
+  static std::shared_ptr<DelegatedHandler> create_empty() {
     struct make_shared_enabler : public DelegatedHandler {};
-
     std::shared_ptr<DelegatedHandler> new_handler =
       std::make_shared<make_shared_enabler>();
+    return new_handler;
+  }
+
+  /*! \brief create DelegatedHandler with initial RootHandler on stack */
+  static std::shared_ptr<DelegatedHandler> create() {
+    std::shared_ptr<DelegatedHandler> new_handler = create_empty();
     new_handler->push_delegate(std::make_shared<RootHandler>(
       new_handler,
       new_handler->result));

tests/cpp/test_frontend.cc

@@ -7,10 +7,13 @@
 #include <gtest/gtest.h>
 #include <gmock/gmock.h>
 #include <rapidjson/document.h>
+#include <fmt/format.h>
 #include <treelite/tree.h>
 #include <treelite/frontend.h>
 #include "xgboost/xgboost_json.h"
 
+using namespace fmt::literals;
+
 namespace treelite {
 
 class MockDelegator : public details::Delegator {
@@ -367,6 +370,64 @@ TEST(RegTreeHandlerSuite, RegTreeHandler) {
   reader.Parse(input_stream, handler);
 }
 
+TEST(RegTreeHandlerSuite, DefaultLeft) {
+  class RegTreeHandlerWrapper : public details::BaseHandler {
+   public:
+    using BaseHandler::BaseHandler;
+    bool StartObject() override {
+      push_handler<details::RegTreeHandler, Tree<float, float>>(output);
+      return true;
+    }
+    Tree<float, float> output;
+  };
+  auto handler = details::DelegatedHandler::create_empty();
+  auto wrapped_handler = std::make_shared<RegTreeHandlerWrapper>(handler);
+  handler->push_delegate(wrapped_handler);
+  rapidjson::Reader reader;
+
+  auto gather_default_left_array = [](const Tree<float, float>& tree) {
+    std::vector<bool> default_left;
+    for (int nid = 0; nid < tree.num_nodes; ++nid) {
+      default_left.push_back(tree.DefaultLeft(nid));
+    }
+    return default_left;
+  };
+
+  // default_left array can be integers; Treelite should automatically cast
+  // the elements to booleans.
+  std::string json_str_fmt = R"JSON(
+  {{"base_weights": [1.0, 0.0, 2.0, -0.5, 0.5, 1.5, 2.5],
+    "default_left": [{default_left}],
+    "id": 0,
+    "left_children": [1, 3, 5, -1, -1, -1, -1],
+    "loss_changes": [4.0, 0.5, 0.5, 0.0, 0.0, 0.0, 0.0],
+    "parents": [2147483647, 0, 0, 1, 1, 2, 2],
+    "right_children": [2, 4, 6, -1, -1, -1, -1],
+    "split_conditions": [2.0, 1.0, 3.0, -0.5, 0.5, 1.5, 2.5],
+    "split_indices": [0, 0, 0, 0, 0, 0, 0],
+    "split_type": [0, 0, 0, 0, 0, 0, 0],
+    "sum_hessian": [4.0, 2.0, 2.0, 1.0, 1.0, 1.0, 1.0],
+    "tree_param": {{
+      "num_deleted": "0",
+      "num_feature": "1",
+      "num_nodes": "7",
+      "size_leaf_vector": "0"}}
+  }})JSON";
+  std::string json_str = fmt::format(json_str_fmt,
+                         "default_left"_a = fmt::join(std::vector<int>{1, 1, 1, 0, 0, 0, 0}, ", "));
+  auto input_stream = rapidjson::MemoryStream(json_str.c_str(), json_str.size());
+  ASSERT_TRUE(reader.Parse(input_stream, *handler));
+  std::vector<bool> expected_default_left{true, true, true, false, false, false, false};
+  ASSERT_EQ(gather_default_left_array(wrapped_handler->output), expected_default_left);
+
+  json_str = fmt::format(json_str_fmt,
+                         "default_left"_a = fmt::join(
+                           std::vector<bool>{true, true, true, false, false, false, false}, ", "));
+  input_stream = rapidjson::MemoryStream(json_str.c_str(), json_str.size());
+  ASSERT_TRUE(reader.Parse(input_stream, *handler));
+  ASSERT_EQ(gather_default_left_array(wrapped_handler->output), expected_default_left);
+}
+
 /******************************************************************************
  * GBTreeModelHandler
  * ***************************************************************************/