From fe5f82fd99b6cc4bb5c92d5fbce5aaaef539375f Mon Sep 17 00:00:00 2001
From: Keshav Kini <keshav.kini@gmail.com>
Date: Thu, 10 Dec 2020 18:20:58 -0800
Subject: [PATCH] python36Packages.black: fix broken dependency

In PR #96456, black was upgraded from 19.10b0 to 20.8b1.  This new version of
black depends on the dataclasses module, but that was only introduced into the
standard library in Python 3.7; earlier versions of Python require the backport
package of the same name.  This commit addresses the missing dependency.
---
 pkgs/development/python-modules/black/default.nix | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pkgs/development/python-modules/black/default.nix b/pkgs/development/python-modules/black/default.nix
index f0a25dfb0b1..3346afbb4ab 100644
--- a/pkgs/development/python-modules/black/default.nix
+++ b/pkgs/development/python-modules/black/default.nix
@@ -5,6 +5,7 @@
 , appdirs
 , attrs
 , click
+, dataclasses
 , mypy-extensions
 , pathspec
 , regex
@@ -59,7 +60,7 @@ buildPythonPackage rec {
     toml
     typed-ast
     typing-extensions
-  ];
+  ] ++ lib.optional (pythonOlder "3.7") dataclasses;
 
   meta = with lib; {
     description = "The uncompromising Python code formatter";