MDEV-20842 Crash using versioning plugin functions after plugin was removed from server

Remove plugin functions via item_create_remove() at deinit time.

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

@@ -506,3 +506,9 @@ add period for system_time(`row_start`,`row_end`),
 modify x int after row_start,
 with system versioning;
 create or replace database test;
+#
+# MDEV-20842 Crash using versioning plugin functions after plugin was removed from server
+#
+uninstall plugin test_versioning;
+select trt_begin_ts(0);
+ERROR 42000: FUNCTION trt_begin_ts does not exist

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

@@ -529,5 +529,11 @@ alter table t add `row_start` bigint unsigned as row start,
               modify x int after row_start,
               with system versioning;
 
-
 create or replace database test;
+
+--echo #
+--echo # MDEV-20842 Crash using versioning plugin functions after plugin was removed from server
+--echo #
+uninstall plugin test_versioning;
+--error ER_SP_DOES_NOT_EXIST
+select trt_begin_ts(0);

plugin/versioning/versioning.cc

@@ -175,6 +175,7 @@ static int versioning_plugin_init(void *p __attribute__ ((unused)))
 static int versioning_plugin_deinit(void *p __attribute__ ((unused)))
 {
   DBUG_ENTER("versioning_plugin_deinit");
+  (void) item_create_remove(func_array);
   DBUG_RETURN(0);
 }
 

sql/item_create.cc

@@ -7465,6 +7465,21 @@ int item_create_append(Native_func_registry array[])
   DBUG_RETURN(0);
 }
 
+int item_create_remove(Native_func_registry array[])
+{
+  Native_func_registry *func;
+
+  DBUG_ENTER("item_create_remove");
+
+  for (func= array; func->builder != NULL; func++)
+  {
+    if (my_hash_delete(& native_functions_hash, (uchar*) func))
+      DBUG_RETURN(1);
+  }
+
+  DBUG_RETURN(0);
+}
+
 /*
   Empty the hash table for native functions.
   Note: this code is not thread safe, and is intended to be used at server

sql/item_create.h

@@ -214,6 +214,7 @@ struct Native_func_registry
 
 int item_create_init();
 int item_create_append(Native_func_registry array[]);
+int item_create_remove(Native_func_registry array[]);
 void item_create_cleanup();
 
 Item *create_func_dyncol_create(THD *thd, List<DYNCALL_CREATE_DEF> &list);