MDEV-15978 Add Feature_system_versioning status variable

mysql-test/main/features.result

@@ -13,6 +13,7 @@ Feature_invisible_columns	0
 Feature_json	0
 Feature_locale	0
 Feature_subquery	0
+Feature_system_versioning	0
 Feature_timezone	0
 Feature_trigger	0
 Feature_window_functions	0

mysql-test/suite/versioning/r/sysvars.result

@@ -126,4 +126,7 @@ select * from t for system_time between '0-0-0' and current_timestamp(6);
 a
 2
 1
+show status like "Feature_system_versioning";
+Variable_name	Value
+Feature_system_versioning	2
 drop table t;

mysql-test/suite/versioning/t/sysvars.test

@@ -84,4 +84,6 @@ select * from t for system_time all;
 select * from t for system_time from '0-0-0' to current_timestamp(6);
 select * from t for system_time between '0-0-0' and current_timestamp(6);
 
+show status like "Feature_system_versioning";
+
 drop table t;

sql/mysqld.cc

@@ -8558,6 +8558,7 @@ SHOW_VAR status_vars[]= {
   {"Feature_json",             (char*) offsetof(STATUS_VAR, feature_json), SHOW_LONG_STATUS},
   {"Feature_locale",           (char*) offsetof(STATUS_VAR, feature_locale), SHOW_LONG_STATUS},
   {"Feature_subquery",         (char*) offsetof(STATUS_VAR, feature_subquery), SHOW_LONG_STATUS},
+  {"Feature_system_versioning",   (char*) offsetof(STATUS_VAR, feature_system_versioning), SHOW_LONG_STATUS},
   {"Feature_timezone",         (char*) offsetof(STATUS_VAR, feature_timezone), SHOW_LONG_STATUS},
   {"Feature_trigger",          (char*) offsetof(STATUS_VAR, feature_trigger), SHOW_LONG_STATUS},
   {"Feature_window_functions", (char*) offsetof(STATUS_VAR, feature_window_functions), SHOW_LONG_STATUS},

sql/sql_class.h

@@ -823,6 +823,7 @@ typedef struct system_status_var
   ulong feature_json;		    /* +1 when JSON function appears in the statement */
   ulong feature_locale;		    /* +1 when LOCALE is set */
   ulong feature_subquery;	    /* +1 when subqueries are used */
+  ulong feature_system_versioning;  /* +1 opening a table WITH SYSTEM VERSIONING */
   ulong feature_timezone;	    /* +1 when XPATH is used */
   ulong feature_trigger;	    /* +1 opening a table with triggers */
   ulong feature_xml;		    /* +1 when XPATH is used */

sql/table.cc

@@ -1777,6 +1777,7 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
     vers_can_native= plugin_hton(se_plugin)->flags & HTON_NATIVE_SYS_VERSIONING;
     row_start_field= row_start;
     row_end_field= row_end;
+    status_var_increment(thd->status_var.feature_system_versioning);
   } // if (system_period == NULL)
 
   for (i=0 ; i < share->fields; i++, strpos+=field_pack_length, field_ptr++)