bpython: substituteAll the path to which

This is used to detect the presence of xclip and other clipboard
handling tools.

Fixes https://github.com/NixOS/nixpkgs/issues/56941.

pkgs/development/python-modules/bpython/clipboard-make-which-substitutable.patch

@@ -0,0 +1,27 @@
+From 6f544a5bd43446859754cb80e012af933b843db9 Mon Sep 17 00:00:00 2001
+From: Florian Klink <flokli@flokli.de>
+Date: Wed, 3 Jun 2020 22:05:34 +0200
+Subject: [PATCH] clipboard: make which substitutable
+
+This is used to detect the presence of xclip and other clipboard
+handling tools.
+---
+ bpython/clipboard.py | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/bpython/clipboard.py b/bpython/clipboard.py
+index aee429b..f346429 100644
+--- a/bpython/clipboard.py
++++ b/bpython/clipboard.py
+@@ -58,7 +58,7 @@ class OSXClipboard(object):
+ 
+ def command_exists(command):
+     process = subprocess.Popen(
+-        ["which", command], stderr=subprocess.STDOUT, stdout=subprocess.PIPE
++        ["@which@", command], stderr=subprocess.STDOUT, stdout=subprocess.PIPE
+     )
+     process.communicate()
+ 
+-- 
+2.26.2
+

pkgs/development/python-modules/bpython/default.nix

@@ -1,4 +1,14 @@
-{ stdenv, buildPythonPackage, fetchPypi, pygments, greenlet, curtsies, urwid, requests, mock }:
+{ stdenv
+, buildPythonPackage
+, fetchPypi
+, curtsies
+, greenlet
+, mock
+, pygments
+, requests
+, substituteAll
+, urwid
+, which }:
 
 buildPythonPackage rec {
   pname = "bpython";
@@ -9,6 +19,11 @@ buildPythonPackage rec {
     sha256 = "1764ikgj24jjq46s50apwkydqvy5a13adb2nbszk8kbci6df0v27";
   };
 
+  patches = [ (substituteAll {
+    src = ./clipboard-make-which-substitutable.patch;
+    which = "${which}/bin/which";
+  })];
+
   propagatedBuildInputs = [ curtsies greenlet pygments requests urwid ];
 
   postInstall = ''