Support categorical split in tree model dump. (#7036)

include/xgboost/feature_map.h

@@ -1,5 +1,5 @@
 /*!
- * Copyright 2014 by Contributors
+ * Copyright 2014-2021 by Contributors
  * \file feature_map.h
  * \brief Feature map data structure to help visualization and model dump.
  * \author Tianqi Chen
@@ -26,7 +26,8 @@ class FeatureMap {
     kIndicator = 0,
     kQuantitive = 1,
     kInteger = 2,
-    kFloat = 3
+    kFloat = 3,
+    kCategorical = 4
   };
   /*!
    * \brief load feature map from input stream
@@ -82,6 +83,7 @@ class FeatureMap {
     if (!strcmp("q", tname)) return kQuantitive;
     if (!strcmp("int", tname)) return kInteger;
     if (!strcmp("float", tname)) return kFloat;
+    if (!strcmp("categorical", tname)) return kCategorical;
     LOG(FATAL) << "unknown feature type, use i for indicator and q for quantity";
     return kIndicator;
   }