Bug #50096: CONCAT_WS inside procedure returning wrong data

Selecting of the CONCAT_WS(...<PS parameter>...) result into
a user variable may return wrong data.

Item_func_concat_ws::val_str contains a number of memory
allocation-saving optimization tricks. After the fix
for bug 46815 the control flow has been changed to a
branch that is commented as "This is quite uncommon!":
one of places where we are trying to concatenate
strings inplace. However, that "uncommon" place
didn't care about PS parameters, that have another
trick in Item_sp_variable::val_str(): they use the
intermediate Item_sp_variable::str_value field,
where they may store a reference to an external
argument's buffer.

The Item_func_concat_ws::val_str function has been
modified to take into account val_str functions
(such as Item_sp_variable::val_str) that return a
pointer to an internal Item member variable that
may reference to a buffer provided.

mysql-test/r/func_concat.result

 DROP TABLE IF EXISTS t1;
+DROP PROCEDURE IF EXISTS p1;
 CREATE TABLE t1 ( number INT NOT NULL, alpha CHAR(6) NOT NULL );
 INSERT INTO t1 VALUES (1413006,'idlfmv'),
 (1413065,'smpsfz'),(1413127,'sljrhx'),(1413304,'qerfnd');
@@ -119,4 +120,14 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	index	NULL	PRIMARY	102	NULL	3	Using index
 1	SIMPLE	t1	eq_ref	PRIMARY,a	PRIMARY	318	func,const,const	1	
 DROP TABLE t1, t2;
+#
+# Bug #50096: CONCAT_WS inside procedure returning wrong data
+#
+CREATE PROCEDURE p1(a varchar(255), b int, c int)
+SET @query = CONCAT_WS(",", a, b, c);
+CALL p1("abcde", "0", "1234");
+SELECT @query;
+@query
+abcde,0,1234
+DROP PROCEDURE p1;
 # End of 5.1 tests

mysql-test/t/func_concat.test

@@ -4,6 +4,7 @@
 
 --disable_warnings
 DROP TABLE IF EXISTS t1;
+DROP PROCEDURE IF EXISTS p1;
 --enable_warnings
 
 CREATE TABLE t1 ( number INT NOT NULL, alpha CHAR(6) NOT NULL );
@@ -111,4 +112,16 @@ EXPLAIN SELECT CONCAT('gui_', t2.a), t1.d FROM t2
 DROP TABLE t1, t2;
 
 
+--echo #
+--echo # Bug #50096: CONCAT_WS inside procedure returning wrong data
+--echo #
+
+CREATE PROCEDURE p1(a varchar(255), b int, c int)
+  SET @query = CONCAT_WS(",", a, b, c);
+
+CALL p1("abcde", "0", "1234");
+SELECT @query;
+
+DROP PROCEDURE p1;
+
 --echo # End of 5.1 tests

sql/item_strfunc.cc

@@ -677,8 +677,8 @@ String *Item_func_concat_ws::val_str(String *str)
 	     res->length() + sep_str->length() + res2->length())
     {
       /* We have room in str;  We can't get any errors here */
-      if (str == res2)
-      {						// This is quote uncommon!
+      if (str->ptr() == res2->ptr())
+      {						// This is quite uncommon!
 	str->replace(0,0,*sep_str);
 	str->replace(0,0,*res);
       }