[Python-modules-team] Bug#956144: virtualenv: caching of debian wheels breaks pip-installed virtualenv

[Anthony Sottile]

Package: virtualenv
Version: 20.0.16-1
Severity: normal
Tags: patch

Reproduction:

```bash
apt update && apt install -y --no-install-recommends virtualenv
virtualenv venv
venv/bin/pip install virtualenv
venv/bin/virtualenv venv2
venv2/bin/pip install astpretty
```

This was originally reported here: https://github.com/pre-commit/pre-commit/issues/1383

The root cause is virtualenv's appdata cache is poisoned by the debian patched
wheels which results in all invocations by unpatched virtualenv failing by
using debian's cache.  My proposal is to separate debian's cache from the
normal name to prevent this collision.  Here's a patch to the installed code
which fixes this issue:

```diff
--- /usr/lib/python3/dist-packages/virtualenv/seed/via_app_data/via_app_data.py.old	2020-04-07 19:41:09.613187290 +0000
+++ /usr/lib/python3/dist-packages/virtualenv/seed/via_app_data/via_app_data.py2020-04-07 19:41:17.601187290 +0000
@@ -18,7 +18,7 @@
     def __init__(self, options):
         super(FromAppData, self).__init__(options)
         self.symlinks = options.symlink_app_data
-        self.base_cache = self.app_data / "seed-app-data" / "v1.0.1"
+        self.base_cache = self.app_data / "seed-app-data" / "v1.0.1.debian"
 
     @classmethod
     def add_parser_arguments(cls, parser, interpreter, app_data):
```


-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.15.0-91-generic (SMP w/2 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE=C (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: unable to detect

Versions of packages virtualenv depends on:
ii  python3-virtualenv  20.0.16-1

virtualenv recommends no packages.

virtualenv suggests no packages.

-- no debconf information