A fix for bug#4368 '"like" fails in PreparedStatement, crashes

server': the bug occurs when arguments of LIKE function are in 
differentcharacter sets. If these character sets are compatible, 
we create an item-converter. In prepared mode, this item
needs to be created in memory of current prepared statement.

mysql-test/r/ps.result

@@ -259,3 +259,14 @@ execute `
 1234
 1234
 set names default;
+create table t1 (a varchar(10)) charset=utf8;
+insert into t1 (a) values ('yahoo');
+set character_set_connection=latin1;
+prepare stmt from 'select a from t1 where a like ?';
+set @var='google';
+execute stmt using @var;
+a
+execute stmt using @var;
+a
+deallocate prepare stmt;
+drop table t1;

mysql-test/t/ps.test

@@ -261,3 +261,20 @@ execute `
 set names default;
 
 
+# 
+# BUG#4368 "select * from t1 where a like ?" crashes server if a is in utf8
+# and ? is in latin1
+# Check that Item converting latin1 to utf8 (for LIKE function) is created
+# in memory of prepared statement.
+#
+
+create table t1 (a varchar(10)) charset=utf8;
+insert into t1 (a) values ('yahoo');
+set character_set_connection=latin1;
+prepare stmt from 'select a from t1 where a like ?';
+set @var='google';
+execute stmt using @var;
+execute stmt using @var;
+deallocate prepare stmt;
+drop table t1;
+

sql/item_cmpfunc.cc

@@ -211,9 +211,20 @@ void Item_bool_func2::fix_length_and_dec()
       }
       else
       {
-	conv= new Item_func_conv_charset(args[weak],args[strong]->collation.collation);
+        THD *thd= current_thd;
+        /*
+          In case we're in statement prepare, create conversion item
+          in its memory: it will be reused on each execute.
+        */
+        Item_arena *arena= thd->current_arena, backup;
+        if (arena->is_stmt_prepare())
+          thd->set_n_backup_item_arena(arena, &backup);
+	conv= new Item_func_conv_charset(args[weak],
+                                         args[strong]->collation.collation);
+        if (arena->is_stmt_prepare())
+          thd->restore_backup_item_arena(arena, &backup);
         conv->collation.set(args[weak]->collation.derivation);
-        conv->fix_fields(current_thd, 0, &conv);
+        conv->fix_fields(thd, 0, &conv);
       }
       args[weak]= conv ? conv : args[weak];
     }