Bug #3087 CONCAT_WS makes the server die in case of illegal mix of collations

mysql-test/r/func_str.result

@@ -339,6 +339,8 @@ select concat(_latin1'a',_latin2'a',_latin5'a');
 ERROR HY000: Illegal mix of collations (latin1_swedish_ci,COERCIBLE), (latin2_general_ci,COERCIBLE), (latin5_turkish_ci,COERCIBLE) for operation 'concat'
 select concat(_latin1'a',_latin2'a',_latin5'a',_latin7'a');
 ERROR HY000: Illegal mix of collations for operation 'concat'
+select concat_ws(_latin1'a',_latin2'a');
+ERROR HY000: Illegal mix of collations (latin1_swedish_ci,COERCIBLE) and (latin2_general_ci,COERCIBLE) for operation 'concat_ws'
 select FIELD('b','A','B');
 FIELD('b','A','B')
 2

mysql-test/t/func_str.test

@@ -195,6 +195,8 @@ select concat(_latin1'a',_latin2'a');
 select concat(_latin1'a',_latin2'a',_latin5'a');
 --error 1271
 select concat(_latin1'a',_latin2'a',_latin5'a',_latin7'a');
+--error 1267
+select concat_ws(_latin1'a',_latin2'a');
 
 #
 # Test FIELD() and collations

sql/item_strfunc.cc

@@ -628,9 +628,11 @@ void Item_func_concat_ws::fix_length_and_dec()
   max_length=separator->max_length*(arg_count-1);
   for (uint i=0 ; i < arg_count ; i++)
   {
+    DTCollation tmp(collation.collation, collation.derivation);
     max_length+=args[i]->max_length;
     if (collation.aggregate(args[i]->collation))
     {
+      collation.set(tmp); // Restore the previous value
       my_coll_agg_error(collation, args[i]->collation, func_name());
       break;
     }