MDEV-5273 Prepared statement doesn't return metadata after prepare.

        Fix for SHOW GRANTS statement.

sql/sql_acl.cc

@@ -7740,6 +7740,16 @@ static int show_grants_callback(ACL_USER_BASE *role, void *data)
 }
 
 
+void mysql_show_grants_get_fields(THD *thd, List<Item> *fields,
+                                  const char *name)
+{
+  Item_string *field=new (thd->mem_root) Item_string_ascii(thd, "", 0);
+  field->name= (char *) name;
+  field->max_length=1024;
+  fields->push_back(field, thd->mem_root);
+}
+
+
 /*
   SHOW GRANTS;  Send grants for a user to the client
 
@@ -7805,15 +7815,14 @@ bool mysql_show_grants(THD *thd, LEX_USER *lex_user)
   }
   DBUG_ASSERT(rolename || username);
 
-  Item_string *field=new (thd->mem_root) Item_string_ascii(thd, "", 0);
   List<Item> field_list;
-  field->name=buff;
-  field->max_length=1024;
   if (!username)
     strxmov(buff,"Grants for ",rolename, NullS);
   else
     strxmov(buff,"Grants for ",username,"@",hostname, NullS);
-  field_list.push_back(field, thd->mem_root);
+
+  mysql_show_grants_get_fields(thd, &field_list, buff);
+
   if (protocol->send_result_set_metadata(&field_list,
                                          Protocol::SEND_NUM_ROWS |
                                          Protocol::SEND_EOF))

sql/sql_acl.h

@@ -241,6 +241,8 @@ ulong get_table_grant(THD *thd, TABLE_LIST *table);
 ulong get_column_grant(THD *thd, GRANT_INFO *grant,
                        const char *db_name, const char *table_name,
                        const char *field_name);
+void mysql_show_grants_get_fields(THD *thd, List<Item> *fields,
+                                  const char *name);
 bool mysql_show_grants(THD *thd, LEX_USER *user);
 int fill_schema_enabled_roles(THD *thd, TABLE_LIST *tables, COND *cond);
 int fill_schema_applicable_roles(THD *thd, TABLE_LIST *tables, COND *cond);

sql/sql_prepare.cc

@@ -1869,6 +1869,29 @@ static bool mysql_test_show_create_db(Prepared_statement *stmt)
 }
 
 
+/**
+  Validate and prepare for execution SHOW GRANTS statement.
+
+  @param stmt               prepared statement
+
+  @retval
+    FALSE             success
+  @retval
+    TRUE              error, error message is set in THD
+*/
+
+static bool mysql_test_show_grants(Prepared_statement *stmt)
+{
+  DBUG_ENTER("mysql_test_show_grants");
+  THD *thd= stmt->thd;
+  List<Item> fields;
+
+  mysql_show_grants_get_fields(thd, &fields, "Grants for");
+    
+  DBUG_RETURN(send_stmt_metadata(thd, stmt, &fields));
+}
+
+
 /**
   @brief Validate and prepare for execution CREATE VIEW statement
 
@@ -2216,6 +2239,13 @@ static bool check_prepared_statement(Prepared_statement *stmt)
       DBUG_RETURN(FALSE);
     }
     break;
+  case SQLCOM_SHOW_GRANTS:
+    if (!(res= mysql_test_show_grants(stmt)))
+    {
+      /* Statement and field info has already been sent */
+      DBUG_RETURN(FALSE);
+    }
+    break;
   case SQLCOM_CREATE_VIEW:
     if (lex->create_view_mode == VIEW_ALTER)
     {

tests/mysql_client_test.c

@@ -436,6 +436,13 @@ static void test_prepare_simple()
   DIE_UNLESS(mysql_stmt_field_count(stmt) == 2);
   mysql_stmt_close(stmt);
 
+  /* show grants */
+  strmov(query, "SHOW GRANTS");
+  stmt= mysql_simple_prepare(mysql, query);
+  check_stmt(stmt);
+  DIE_UNLESS(mysql_stmt_field_count(stmt) == 1);
+  mysql_stmt_close(stmt);
+
   /* now fetch the results ..*/
   rc= mysql_commit(mysql);
   myquery(rc);