tox: fix environment setup

Use the virtualenv's pip for installing dependencies, not the
code that is about to be tested.

commit 922f9a3f6dc4ac642492204808b4d5cc995aca66
Author: Benoit Pierre <[email protected]>
Date:   Wed Aug 9 02:47:39 2017 +0200

    tox/travis: fix and rework handling of un-vendored jobs

Author: benoit-pierre

.tox_helpers/runpip.py

@@ -0,0 +1,45 @@
+from glob import glob
+import distutils.sysconfig
+import os
+import shutil
+import subprocess
+import sys
+
+
+VIRTUAL_ENV = os.environ['VIRTUAL_ENV']
+TOX_PIP_DIR = os.path.join(VIRTUAL_ENV, 'pip')
+SITE_PACKAGES = distutils.sysconfig.get_python_lib()
+
+
+def pip(args):
+    # First things first, safeguard the environment
+    # original pip so it can be used for all calls.
+    if not os.path.exists(TOX_PIP_DIR):
+        os.mkdir(TOX_PIP_DIR)
+        # Remove executable/launchers.
+        for entry in glob(os.path.join(VIRTUAL_ENV, 'bin', 'pip*')):
+            os.unlink(entry)
+        # Relocate package and distribution info.
+        for src in (
+            os.path.join(SITE_PACKAGES, 'pip'),
+            glob(os.path.join(SITE_PACKAGES, 'pip-*.dist-info'))[0],
+        ):
+            shutil.move(src, TOX_PIP_DIR)
+        # Create a very simple launcher that
+        # can be used for Linux and Windows.
+        with open(os.path.join(TOX_PIP_DIR, 'pip.py'), 'w') as fp:
+            fp.write('from pip import main; main()\n')
+    # And use a temporary copy of that version
+    # so it can uninstall itself if needed.
+    temp_pip = TOX_PIP_DIR + '.tmp'
+    try:
+        shutil.copytree(TOX_PIP_DIR, temp_pip)
+        cmd = [sys.executable, os.path.join(temp_pip, 'pip.py')]
+        cmd.extend(args)
+        subprocess.check_call(cmd)
+    finally:
+        shutil.rmtree(temp_pip)
+
+
+if __name__ == '__main__':
+    pip(sys.argv[1:])

MANIFEST.in

@@ -19,6 +19,7 @@ recursive-include pip/_vendor *.pem
 recursive-include docs Makefile *.rst *.py *.bat
 
 prune .github
+prune .tox_helpers
 prune .travis
 prune docs/_build
 prune news

tox.ini

@@ -3,14 +3,20 @@ envlist =
     docs, packaging, lint-py2, lint-py3,
     py27, py33, py34, py35, py36, py37, pypy
 
+[helpers]
+# Wrapper for calls to pip that make sure the version being used is the
+# original virtualenv (stable) version, and not the code being tested.
+pip = python {toxinidir}/.tox_helpers/runpip.py
+
 [testenv]
 setenv =
     # This is required in order to get UTF-8 output inside of the subprocesses
     # that our tests use.
     LC_CTYPE = en_US.UTF-8
 deps = -r{toxinidir}/dev-requirements.txt
 commands = py.test --timeout 300 []
-install_command = python -m pip install {opts} {packages}
+install_command = {[helpers]pip} install {opts} {packages}
+list_dependencies_command = {[helpers]pip} freeze
 
 [testenv:docs]
 deps = sphinx == 1.6.1