Remove the side effect of setting m_sp from Item_sp::init_result_field

Item_sp::init_result_field no longer takes sp_head* parameter. It
expects the m_sp member to be already set to something valid.

sql/item.cc

@@ -2915,21 +2915,14 @@ Item_sp::execute_impl(THD *thd, Item **args, uint arg_count)
 */
 
 bool
-Item_sp::init_result_field(THD *thd, sp_head *sp, uint max_length,
-                           uint maybe_null, bool *null_value, LEX_CSTRING *name)
+Item_sp::init_result_field(THD *thd, uint max_length, uint maybe_null,
+                           bool *null_value, LEX_CSTRING *name)
 {
   DBUG_ENTER("Item_sp::init_result_field");
 
-  DBUG_ASSERT(m_sp == NULL);
+  DBUG_ASSERT(m_sp != NULL);
   DBUG_ASSERT(sp_result_field == NULL);
 
-  if (!(m_sp= sp))
-  {
-    my_missing_function_error (m_name->m_name, ErrConvDQName(m_name).ptr());
-    context->process_error(thd);
-    DBUG_RETURN(TRUE);
-  }
-
   /*
      A Field needs to be attached to a Table.
      Below we "create" a dummy table by initializing

sql/item.h

@@ -4496,8 +4496,8 @@ class Item_sp
   bool sp_check_access(THD *thd);
   bool execute(THD *thd, bool *null_value, Item **args, uint arg_count);
   bool execute_impl(THD *thd, Item **args, uint arg_count);
-  bool init_result_field(THD *thd, sp_head *sp, uint max_length,
-                         uint maybe_null, bool *null_value, LEX_CSTRING *name);
+  bool init_result_field(THD *thd, uint max_length, uint maybe_null,
+                         bool *null_value, LEX_CSTRING *name);
 };
 
 class Item_ref :public Item_ident

sql/item_func.cc

@@ -6415,12 +6415,28 @@ Item_func_sp::fix_fields(THD *thd, Item **ref)
     }
   }
 
+
+  /* Custom aggregates are transformed into an Item_sum_sp. We can not do this
+     earlier as we have no way of knowing what kind of Item we should create
+     when parsing the query.
+
+     TODO(cvicentiu): See if this limitation can be lifted.
+  */
+
+  DBUG_ASSERT(m_sp == NULL);
+  if (!(m_sp= sp))
+  {
+    my_missing_function_error(m_name->m_name, ErrConvDQName(m_name).ptr());
+    context->process_error(thd);
+    DBUG_RETURN(TRUE);
+  }
+
   /*
-    We must call init_result_field before Item_func::fix_fields() 
+    We must call init_result_field before Item_func::fix_fields()
     to make m_sp and result_field members available to fix_length_and_dec(),
     which is called from Item_func::fix_fields().
   */
-  res= init_result_field(thd, sp, max_length, maybe_null, &null_value, &name);
+  res= init_result_field(thd, max_length, maybe_null, &null_value, &name);
 
   if (res)
     DBUG_RETURN(TRUE);