A fix and a test case for Bug#9359 "Prepared statements take snapshot

 of system vars at PREPARE time": implement a special Item
to handle system variables. This item substitutes itself with 
a basic constant containing variable value at fix_fields.


mysql-test/r/ps.result:
  - test results fixed (Bug#9359).
mysql-test/t/ps.test:
  - add a test case for Bug#9359 "Prepared statements take snapshot
   of system vars at PREPARE time"
sql/item_func.cc:
  - implement Item_func_get_system_var: we should not evaluate system
  variables in the parser, but instead should create an item which 
  is evaluated to a constant at execute.
  - remove an unused function
sql/item_func.h:
  Add a new item, Item_func_get_system_var
sql/mysql_priv.h:
  Move necessary declarations to make set_var.h objects visible in 
  item_func.h
sql/set_var.cc:
  - we should not print to network from get_system_var: if it's called
  from prepared statement prepare, we get packets out of order when using
  the binary protocol. Instead report the error to be sent to the user later.
  This is a backport from 5.0.
sql/set_var.h:
  - declaration of enum_var_type moved to mysql_priv.h

1 files changed, 3 insertions, 11 deletions

diff --git a/sql/set_var.cc b/sql/set_var.cc
index b0fa61a12bc..f7700d18607 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -1551,15 +1551,7 @@ err:
 
 /*
   Return an Item for a variable.  Used with @@[global.]variable_name
-
   If type is not given, return local value if exists, else global
-
-  We have to use netprintf() instead of my_error() here as this is
-  called on the parsing stage.
-
-  TODO:
-    With prepared statements/stored procedures this has to be fixed
-    to create an item that gets the current value at fix_fields() stage.
 */
 
 Item *sys_var::item(THD *thd, enum_var_type var_type, LEX_STRING *base)
@@ -1568,8 +1560,8 @@ Item *sys_var::item(THD *thd, enum_var_type var_type, LEX_STRING *base)
   {
     if (var_type != OPT_DEFAULT)
     {
-      net_printf(thd, ER_INCORRECT_GLOBAL_LOCAL_VAR,
-		 name, var_type == OPT_GLOBAL ? "SESSION" : "GLOBAL");
+      my_error(ER_INCORRECT_GLOBAL_LOCAL_VAR, MYF(0),
+               name, var_type == OPT_GLOBAL ? "SESSION" : "GLOBAL");
       return 0;
     }
     /* As there was no local variable, return the global value */
@@ -1613,7 +1605,7 @@ Item *sys_var::item(THD *thd, enum_var_type var_type, LEX_STRING *base)
     return tmp;
   }
   default:
-    net_printf(thd, ER_VAR_CANT_BE_READ, name);
+    my_error(ER_VAR_CANT_BE_READ, MYF(0), name);
   }
   return 0;
 }