Fix for bug #1500 "Server crash with mysql_prepare"

We treat Item_param whose value is not set as non-const.
This allows us to avoid use of Item_param's value (not yet existing) in 
those fix_fields and fix_length_and_dec that do calculations if their 
Items arguments are const. So we can call fix_fields for such items from
mysql_prepare safely.


sql/item.cc:
  Now Item_param is non-constant (const_item()==FALSE) until its value is set.
sql/item.h:
  Added Item::const_during_execution() method which indicates constants that will be known 
  during execution phase (but they may be not known during preparing phase for example parameters 
  of prep. statements.)
  Made Item_param non-constant until its is value set, so its value won't be requested during 
  prepare statement step.
sql/item_func.cc:
  Fulltext search AGAINST clause now allows prepared statement parameter as its argument.
  Removed duplicate used_tables_cache update in Item_func_match::fix_fields()
  (it is set during Item_func::fix_fields).
tests/client_test.c:
  Added test for bug #1500 "Server crash with mysql_prepare"

1 files changed, 19 insertions, 0 deletions

diff --git a/sql/item.h b/sql/item.h
index 8b35705f191..1e62e863ab7 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -173,7 +173,17 @@ public:
   virtual cond_result eq_cmp_result() const { return COND_OK; }
   inline uint float_length(uint decimals_par) const
   { return decimals != NOT_FIXED_DEC ? (DBL_DIG+2+decimals_par) : DBL_DIG+8;}
+  /* 
+    Returns true if this is constant (during query execution, i.e. its value
+    will not change until next fix_fields) and its value is known.
+  */
   virtual bool const_item() const { return used_tables() == 0; }
+  /* 
+    Returns true if this is constant but its value may be not known yet.
+    (Can be used for parameters of prep. stmts or of stored procedures.)
+  */
+  virtual bool const_during_execution() const 
+  { return (used_tables() & ~PARAM_TABLE_BIT) == 0; }
   virtual void print(String *str_arg) { str_arg->append(full_name()); }
   void print_item_w_name(String *);
   virtual void update_used_tables() {}
@@ -318,6 +328,7 @@ public:
 class Item_param :public Item
 {
 public:    
+  bool value_is_set;
   longlong int_value;
   double   real_value;
   TIME     ltime;
@@ -336,6 +347,7 @@ public:
     item_result_type = STRING_RESULT;
     item_is_time= false;
     long_data_supplied= false;
+    value_is_set= 0;
   }
   enum Type type() const { return item_type; }
   double val();
@@ -363,6 +375,13 @@ public:
   String *query_val_str(String *str);
   enum_field_types field_type() const { return MYSQL_TYPE_STRING; }
   Item *new_item() { return new Item_param(pos_in_query); }
+  /* 
+    If value for parameter was not set we treat it as non-const 
+    so noone will use parameters value in fix_fields still 
+    parameter is constant during execution.
+  */
+  virtual table_map used_tables() const
+  { return value_is_set ? (table_map)0 : PARAM_TABLE_BIT; }
   void print(String *str) { str->append('?'); }
 };