From 8fe1c105dfbe9da4b51ff3e92c64da5529736bd7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andreas=20Kl=C3=B6ckner?= <inform@tiker.net>
Date: Mon, 11 Oct 2021 13:31:15 -0500
Subject: [PATCH] Revert "remove deprecation of specifying the direction vector
 name"

This reverts commit eed67c28c1419bb1abd3ab898d9bd0e6edf010fc.
---
 sumpy/kernel.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sumpy/kernel.py b/sumpy/kernel.py
index 859b2dbde..1db8f11c7 100644
--- a/sumpy/kernel.py
+++ b/sumpy/kernel.py
@@ -1077,6 +1077,10 @@ class DirectionalDerivative(DerivativeBase):
     def __init__(self, inner_kernel, dir_vec_name=None):
         if dir_vec_name is None:
             dir_vec_name = self.directional_kind + "_derivative_dir"
+        else:
+            from warnings import warn
+            warn("specified the name of the direction vector",
+                    stacklevel=2)
 
         KernelWrapper.__init__(self, inner_kernel)
         self.dir_vec_name = dir_vec_name