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, 23 insertions, 0 deletions

diff --git a/sql/item_func.h b/sql/item_func.h
index 6b6e5d4b8ec..5e36f9863bb 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -988,6 +988,29 @@ public:
 };
 
 
+/* A system variable */
+
+class Item_func_get_system_var :public Item_func
+{
+  sys_var *var;
+  enum_var_type var_type;
+  LEX_STRING component;
+public:
+  Item_func_get_system_var(sys_var *var_arg, enum_var_type var_type_arg,
+                           LEX_STRING *component_arg, const char *name_arg,
+                           size_t name_len_arg);
+  bool fix_fields(THD *thd, TABLE_LIST *tables, Item **ref);
+  /*
+    Stubs for pure virtual methods. Should never be called: this
+    item is always substituted with a constant in fix_fields().
+  */
+  double val()              { DBUG_ASSERT(0); return 0.0; }
+  longlong val_int()        { DBUG_ASSERT(0); return 0; }
+  String* val_str(String*)  { DBUG_ASSERT(0); return 0; }
+  void fix_length_and_dec() { DBUG_ASSERT(0); }
+};
+
+
 class Item_func_inet_aton : public Item_int_func
 {
 public: