MDEV-27306: SET STATEMENT optimizer_trace=1 Doesn't save the tracebb-10.6-mdev27306

In mysql_execute_command(), move optimizer trace initialization to be
after run_set_statement_if_requested() call.

Unfortunately, mysql_execute_command() code uses "goto error" a lot, and
this means optimizer trace code cannot use RAII objects. Work this around
by:
- Make Opt_trace_start a non-RAII object, add init() method.
- Move the code that writes the top-level object and array into
  Opt_trace_start::init().

1 files changed, 5 insertions, 6 deletions

diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index 2a48c8fb1ce..0886fc85151 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -3644,12 +3644,7 @@ mysql_execute_command(THD *thd, bool is_called_from_prepared_stmt)
 #ifdef HAVE_REPLICATION
   } /* endif unlikely slave */
 #endif
-  Opt_trace_start ots(thd, all_tables, lex->sql_command, &lex->var_list,
-                      thd->query(), thd->query_length(),
-                      thd->variables.character_set_client);
-
-  Json_writer_object trace_command(thd);
-  Json_writer_array trace_command_steps(thd, "steps");
+  Opt_trace_start ots(thd);
 
   /* store old value of binlog format */
   enum_binlog_format orig_binlog_format,orig_current_stmt_binlog_format;
@@ -3715,6 +3710,10 @@ mysql_execute_command(THD *thd, bool is_called_from_prepared_stmt)
   if (run_set_statement_if_requested(thd, lex))
     goto error;
 
+  /* After SET STATEMENT is done, we can initialize the Optimizer Trace: */
+  ots.init(thd, all_tables, lex->sql_command, &lex->var_list, thd->query(),
+           thd->query_length(), thd->variables.character_set_client);
+
   if (thd->lex->mi.connection_name.str == NULL)
       thd->lex->mi.connection_name= thd->variables.default_master_connection;