cannot allocate a new String[] in the ::val_str() method

String inherits from Sql_alloc, so it's allocated on the thd's memroot,
this cannot be done per row.

Moved String[] allocation into the Item_func_sformat constructor
(not fix_fields(), because we want it on the same memroot where the item
is).

mysql-test/main/func_sformat.result

@@ -437,3 +437,15 @@ t1	CREATE TABLE `t1` (
   `x` varchar(8) CHARACTER SET ucs2 DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
+#
+# ps parameters
+#
+prepare s from 'select sformat("={:d}=", ?)';
+execute s using 100;
+sformat("={:d}=", ?)
+=100=
+execute s using 'abc';
+sformat("={:d}=", ?)
+NULL
+Warnings:
+Warning	4183	SFORMAT error: invalid type specifier

mysql-test/main/func_sformat.test

@@ -199,3 +199,11 @@ select hex(sformat(_ucs2 x'003D007B007D003D', _ucs2 x'0442043504410442'));
 create table t1 as select sformat(_ucs2 x'003D007B007D003D', _ucs2 x'0442043504410442') as x;
 show create table t1;
 drop table t1;
+
+
+echo #;
+echo # ps parameters;
+echo #;
+prepare s from 'select sformat("={:d}=", ?)';
+execute s using 100;
+execute s using 'abc';

sql/item_strfunc.cc

@@ -1306,9 +1306,22 @@ bool Item_func_replace::fix_length_and_dec()
   return FALSE;
 }
 
+/*
+  this is done in the constructor to be in the same memroot as
+  the item itself
+*/
+Item_func_sformat::Item_func_sformat(THD *thd, List<Item> &list)
+  : Item_str_func(thd, list)
+{
+  val_arg= new (thd->mem_root) String[arg_count];
+}
+
 
 bool Item_func_sformat::fix_length_and_dec()
 {
+  if (!val_arg)
+    return TRUE;
+
   ulonglong char_length= 0;
 
   uint flags= MY_COLL_ALLOW_SUPERSET_CONV |
@@ -1361,7 +1374,6 @@ String *Item_func_sformat::val_str(String *res)
   using                         ctx=     fmt::format_context;
   String                       *fmt_arg= NULL;
   String                       *parg=    NULL;
-  String                       *val_arg= NULL;
   fmt::format_args::format_arg *vargs=   NULL;
 
   null_value= true;
@@ -1371,12 +1383,6 @@ String *Item_func_sformat::val_str(String *res)
   if (!(vargs= new fmt::format_args::format_arg[arg_count - 1]))
     return NULL;
 
-  if (!(val_arg= new String[arg_count - 1]))
-  {
-    delete [] vargs;
-    return NULL;
-  }
-
   /* Creates the array of arguments for vformat */
   for (uint carg= 1; carg < arg_count; carg++)
   {
@@ -1393,7 +1399,6 @@ String *Item_func_sformat::val_str(String *res)
       if (!(parg= args[carg]->val_str(&val_arg[carg-1])))
       {
         delete [] vargs;
-        delete [] val_arg;
         return NULL;
       }
       if (parg->length() == 1)
@@ -1406,7 +1411,6 @@ String *Item_func_sformat::val_str(String *res)
     default:
       DBUG_ASSERT(0);
       delete [] vargs;
-      delete [] val_arg;
       return NULL;
     }
   }
@@ -1430,7 +1434,6 @@ String *Item_func_sformat::val_str(String *res)
     null_value= true;
   }
   delete [] vargs;
-  delete [] val_arg;
   return null_value ? NULL : res;
 }
 

sql/item_strfunc.h

@@ -588,9 +588,10 @@ public:
 
 class Item_func_sformat :public Item_str_func
 {
+  String *val_arg;
 public:
-  Item_func_sformat(THD *thd, List<Item> &list):
-    Item_str_func(thd, list) { }
+  Item_func_sformat(THD *thd, List<Item> &list);
+  ~Item_func_sformat() { delete [] val_arg; }
   String *val_str(String*) override;
   bool fix_length_and_dec() override;
   LEX_CSTRING func_name_cstring() const override