[RFC] setting proper result codes

["Martin M. Hunt" <hunt at redhat dot com>]

Due to some changes made some time ago, most C functions are incorrectly setting error messages.  For example:

  Tcl_SetStringObj (result_ptr->obj_ptr, "type must be \"temp\" or \"normal\"", -1);

- or - 

  {
      char *err_buf;
      xasprintf (&err_buf, "Breakpoint #%d does not exist.", bpnum);
      Tcl_SetStringObj (result_ptr->obj_ptr, err_buf, -1);
      free(err_buf);
      return TCL_ERROR;
    }

The above examples do not actually cause an error message to be displayed.  
Using Tcl_SetObjResult() fixes this, but is a bit awkward.  For example, the first
example needs to be:

Tcl_SetObjResult (interp, Tcl_NewStringObj ("type must be \"temp\" or \"normal\"", -1));

The second example is even worse.  So I am proposing using the following for all error messages
in our C tcl functions:

void
set_result (Tcl_Interp *interp, const char *fmt,...)
{
  va_list args;
  char *buf;

  va_start (args, fmt);
  xvasprintf (&buf, fmt, args);
  va_end (args);
  Tcl_SetObjResult (interp, Tcl_NewStringObj (buf, -1));
  free(buf);
}

so in each function, you just do something like:
  set_result (interp, "the line number %d is invalid.", line_number);

This seems obvious. Am I understanding the problem fully?  Any objections or suggestions?

-- 
Martin Hunt
GDB Engineer
Red Hat, Inc.