MySQL Bugs: #74159: prototype for SHOW_FUNC handler declared as return int but return value ignored?

Bug #74159	prototype for SHOW_FUNC handler declared as return int but return value ignored?
Submitted:	30 Sep 2014 15:53	Modified:	30 Sep 2014 16:24
Reporter:	Hartmut Holzgraefe	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Compiling	Severity:	S3 (Non-critical)
Version:	MySQL 5.6.20	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
The mysql_show_var_func typedef for SHOW_FUNC callback handlers is declared as returning "int", but at the two places where it gets called in SHOW STATUS handling its return value is completely ignored.

Also the documentation mentions that it should return int (by showing the typedef prototype) but doesn't mention what to return at all.

How to repeat:
Check ./include/mysql/plugin.h:

  typedef int (*mysql_show_var_func)(MYSQL_THD, struct st_mysql_show_var*, char *);

vs. sql/sql_show.cc

  /*
  if var->type is SHOW_FUNC, call the function.
  Repeat as necessary, if new var is again SHOW_FUNC
  */
  SHOW_VAR tmp;
  for (; list->type == SHOW_FUNC; list= &tmp)
    ((mysql_show_var_func)(list->value))(thd, &tmp, value);

and

  /*
    if var->type is SHOW_FUNC or SHOW_SIMPLE_FUNC, call the function.        
    Repeat as necessary, if new var is again one of the above
  */                                                                         
  for (var=variables; var->type == SHOW_FUNC ||                              
         var->type == SHOW_SIMPLE_FUNC; var= &tmp)                           
    ((mysql_show_var_func)(var->value))(thd, &tmp, buff);                    

Suggested fix:
The return value was probably meant to signal errors?

So implement actual error checking where mysql_show_var_func is called?

PS: maybe a general "MySQL Server: Plugin API" in addition to the more specific "MySQL Server: Storage Engine API" one would make sense? I wasn't really sure which category to choose for this one ...

I have carefully studies the code and I must agree with reporter. This is a minor bug, but still a bug. Either return the error or make a function void !!!!