From c4437bd19401a7f9b62111dbebc7e94a585a82ee Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Wed, 8 Jul 2020 13:20:07 -0400
Subject: [PATCH] Package Future 0.18.2 for us

---
 nix/future.nix     | 35 +++++++++++++++++++++++++++++++++++
 nix/overlays.nix   |  5 +++++
 nix/tahoe-lafs.nix |  1 +
 3 files changed, 41 insertions(+)
 create mode 100644 nix/future.nix

diff --git a/nix/future.nix b/nix/future.nix
new file mode 100644
index 000000000..814b7c1b5
--- /dev/null
+++ b/nix/future.nix
@@ -0,0 +1,35 @@
+{ lib
+, buildPythonPackage
+, fetchPypi
+}:
+
+buildPythonPackage rec {
+  pname = "future";
+  version = "0.18.2";
+
+  src = fetchPypi {
+    inherit pname version;
+    sha256 = "sha256:0zakvfj87gy6mn1nba06sdha63rn4njm7bhh0wzyrxhcny8avgmi";
+  };
+
+  doCheck = false;
+
+  meta = {
+    description = "Clean single-source support for Python 3 and 2";
+    longDescription = ''
+      python-future is the missing compatibility layer between Python 2 and
+      Python 3. It allows you to use a single, clean Python 3.x-compatible
+      codebase to support both Python 2 and Python 3 with minimal overhead.
+
+      It provides future and past packages with backports and forward ports
+      of features from Python 3 and 2. It also comes with futurize and
+      pasteurize, customized 2to3-based scripts that helps you to convert
+      either Py2 or Py3 code easily to support both Python 2 and 3 in a
+      single clean Py3-style codebase, module by module.
+    '';
+    homepage = https://python-future.org;
+    downloadPage = https://github.com/PythonCharmers/python-future/releases;
+    license = with lib.licenses; [ mit ];
+    maintainers = with lib.maintainers; [ prikhi ];
+  };
+}
diff --git a/nix/overlays.nix b/nix/overlays.nix
index 2a9fe8e5e..7f19a8f1a 100644
--- a/nix/overlays.nix
+++ b/nix/overlays.nix
@@ -10,6 +10,11 @@ self: super: {
       # NixOS autobahn package has trollius as a dependency, although
       # it is optional. Trollius is unmaintained and fails on CI.
       autobahn = python-super.callPackage ./autobahn.nix { };
+
+      # Porting to Python 3 is greatly aided by the future package.  A
+      # slightly newer version than appears in nixos 19.09 is helpful.
+      future = python-super.callPackage ./future.nix { };
+
     };
   };
 }
diff --git a/nix/tahoe-lafs.nix b/nix/tahoe-lafs.nix
index cc0eea479..ae5c05f70 100644
--- a/nix/tahoe-lafs.nix
+++ b/nix/tahoe-lafs.nix
@@ -50,6 +50,7 @@ python.pkgs.buildPythonPackage rec {
     setuptoolsTrial pyasn1 zope_interface
     service-identity pyyaml magic-wormhole treq
     eliot autobahn cryptography setuptools
+    future
   ];
 
   checkInputs = with python.pkgs; [