Bad virtualenv patch breaking pipenv on Python 3.7.2

[matthew-piziak]

Issue description

Any pipenv command results in this:

Using base prefix '/nix/store/p6x8n1v3axgd48s8il2q97w6408bf67x-python3-3.7.2-env'
Traceback (most recent call last):
  File "/nix/store/clwdqf1zrhv3gcbrrca2cklrs0xkpj26-python3.7-virtualenv-16.4.1/bin/.virtualenv-wrapped", line 11, in <module>
    sys.exit(main())
  File "/nix/store/p6x8n1v3axgd48s8il2q97w6408bf67x-python3-3.7.2-env/lib/python3.7/site-packages/virtualenv.py", line 810, in main
    symlink=options.symlink,
  File "/nix/store/p6x8n1v3axgd48s8il2q97w6408bf67x-python3-3.7.2-env/lib/python3.7/site-packages/virtualenv.py", line 1088, in create_environment
    install_python(home_dir, lib_dir, inc_dir, bin_dir, site_packages=site_packages, clear=clear, symlink=symlink)
  File "/nix/store/p6x8n1v3axgd48s8il2q97w6408bf67x-python3-3.7.2-env/lib/python3.7/site-packages/virtualenv.py", line 1385, in install_python
    wrapper_path = join(prefix, "lib", py_version, "site-packages")
NameError: name 'py_version' is not defined

...which, I mean, yeah, it's not available as far as I can tell, but I think it's a bug resulting from an outdated patch here: https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/python-modules/virtualenv/virtualenv-change-prefix.patch

I hard-coded py_version in that file to the version that I needed, and now I can use pipenv again.

Steps to reproduce

On unstable, install pipenv and try to run pipenv install in an empty directory.

Technical details

• system: "x86_64-linux"
• host os: Linux 4.17.19, NixOS, 18.03.133402.cb0e20d6db9 (Impala)
• multi-user?: yes
• sandbox: no
• version: nix-env (Nix) 2.0.4
• channels(root): "nixpkgs-18.03.133402.cb0e20d6db9, unstable-19.09pre171786.34aa254f9eb"
• channels(matt): "unstable"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixpkgs

[rht]

My current workaround for patching configuration.nix (this is probably more verbose than it should be)

nixpkgs.config.packageOverrides = pkgs : rec {
      python37Packages = pkgs.python37Packages.override (oldAttrs: {
        overrides = self: super: {
          virtualenv = super.virtualenv.overrideAttrs ( z : rec {
            postPatch = ''
              substituteInPlace virtualenv.py --replace "py_version" "PY_VERSION"
            '';
          });
        };
      });

This uncovers more error after creating the virtualenv symlinks: Nvm, it works. I had to do more cleanup in addition to find $VENVPATH -type l delete before refreshing the venv.

Fatal Python error: initfsencoding: Unable to get the locale encoding
LookupError: no codec search functions registered: can't find encoding