Bug#12371 executing prepared statement fails (illegal mix of collations)

item.cc:
item.h:
  Adding Item_param::safe_charset_converter,
  not to return collation mix error if
  parameter can be converted into operation
  character set.

ctype_utf8.result:
  adding test case
ctype_utf8.test:
  adding test case

mysql-test/r/ctype_utf8.result

@@ -993,6 +993,15 @@ select * from t1 where a like "%abc\d%";
 a
 abcd
 drop table t1;
+set names utf8;
+create table t1 (a char(3), b varchar(10));
+insert into t1 values ('bar','kostja');
+prepare my_stmt from "select * from t1 where a=?";
+set @a:='bar';
+execute my_stmt using @a;
+a	b
+bar	kostja
+drop table t1;
 CREATE TABLE t1 (
 a varchar(255) NOT NULL default '',
 KEY a (a)

mysql-test/t/ctype_utf8.test

@@ -831,6 +831,18 @@ select * from t1 where a like "%abc\d%";
 drop table t1;
 
 
+#
+# Bug #12371 executing prepared statement fails (illegal mix of collations)
+#
+set names utf8;
+create table t1 (a char(3), b varchar(10));
+insert into t1 values ('bar','kostja');
+prepare my_stmt from "select * from t1 where a=?";
+set @a:='bar';
+execute my_stmt using @a;
+drop table t1;
+
+
 #
 # Bug#9557 MyISAM utf8 table crash
 #

sql/item.cc

@@ -284,6 +284,26 @@ Item *Item_string::safe_charset_converter(CHARSET_INFO *tocs)
 }
 
 
+Item *Item_param::safe_charset_converter(CHARSET_INFO *tocs)
+{
+  if (const_item())
+  {
+    Item_string *conv;
+    uint conv_errors;
+    String tmp, cstr, *ostr= val_str(&tmp);
+    cstr.copy(ostr->ptr(), ostr->length(), ostr->charset(), tocs, &conv_errors);
+    if (conv_errors || !(conv= new Item_string(cstr.ptr(), cstr.length(),
+                                               cstr.charset(),
+                                               collation.derivation)))
+      return NULL;
+    conv->str_value.copy();
+    conv->str_value.shrink_to_length();
+    return conv;
+  }
+  return NULL;
+}
+
+
 bool Item_string::eq(const Item *item, bool binary_cmp) const
 {
   if (type() == item->type() && item->basic_const_item())

sql/item.h

@@ -617,6 +617,7 @@ public:
     basic_const_item returned TRUE.
   */
   Item *new_item();
+  Item *safe_charset_converter(CHARSET_INFO *tocs);
   /*
     Implement by-value equality evaluation if parameter value
     is set and is a basic constant (integer, real or string).