Use a helper for ensure tox always runs a known-good pip version.

tools/tox_pip.py

@@ -0,0 +1,91 @@
+"""A simple wrapper to ensure tox always uses a known-good pip.
+"""
+
+import distutils.sysconfig
+import itertools
+import os
+import shutil
+import subprocess
+import sys
+from glob import glob
+from os.path import basename, exists, join
+
+VIRTUAL_ENV = os.environ["VIRTUAL_ENV"]
+SITE_PACKAGES = distutils.sysconfig.get_python_lib()
+
+TOX_PIP_DIR = join(VIRTUAL_ENV, "pip-backup")
+EXECUTABLE_BACKUP = join(TOX_PIP_DIR, "bin")
+PACKAGE_BACKUP = join(TOX_PIP_DIR, "package")
+
+
+# Logic for finding the right files
+def get_installed_files(where):
+    sources = join(where, "pip")
+    dist_infos = glob(join(where, "pip-*.dist-info"))
+    egg_stuff = glob(join(where, "pip*.egg-*"))
+
+    return filter(exists, itertools.chain([sources], dist_infos, egg_stuff))
+
+
+def get_binaries(where):
+    return glob(join(where, "bin", "pip*"))
+
+
+# Logic for moving the files around.
+def backup_as_known_good():
+    # Make the backup directory
+    os.mkdir(TOX_PIP_DIR)
+
+    # Copy executable/launchers.
+    os.mkdir(EXECUTABLE_BACKUP)
+    for entry in get_binaries(VIRTUAL_ENV):
+        shutil.copy2(entry, join(EXECUTABLE_BACKUP, basename(entry)))
+
+    # Copy package and distribution info.
+    os.mkdir(PACKAGE_BACKUP)
+    for path in get_installed_files(SITE_PACKAGES):
+        shutil.copytree(path, join(PACKAGE_BACKUP, basename(path)))
+
+
+def remove_existing_installation():
+    # Remove executables/launchers.
+    for entry in get_binaries(VIRTUAL_ENV):
+        os.unlink(entry)
+
+    # Remove package and distribution info.
+    for path in get_installed_files(SITE_PACKAGES):
+        if os.path.isfile(path):
+            os.unlink(path)
+        else:
+            shutil.rmtree(path)
+
+
+def install_known_good_pip():
+    # Copy executables/launchers.
+    for entry in get_binaries(TOX_PIP_DIR):
+        shutil.copy2(entry, join(VIRTUAL_ENV, "bin", basename(entry)))
+
+    # Move package and distribution info.
+    for path in get_installed_files(PACKAGE_BACKUP):
+        shutil.copytree(path, join(SITE_PACKAGES, basename(path)))
+
+
+def run(args):
+    # First things first, safeguard the environment original pip so it can be
+    # used for all calls.
+    if not exists(TOX_PIP_DIR):
+        backup_as_known_good()
+
+    remove_existing_installation()
+    install_known_good_pip()
+
+    # Run the command.
+    #   We just do a python -m pip here because this is a known good pip, which
+    #   is expected to work properly.
+    cmd = [sys.executable, "-m", "pip"]
+    cmd.extend(args)
+    subprocess.check_call(cmd)
+
+
+if __name__ == "__main__":
+    run(sys.argv[1:])

tox.ini

@@ -1,37 +1,46 @@
 [tox]
+skipsdist = True
 envlist =
     docs, packaging, lint-py2, lint-py3, mypy,
     py27, py34, py35, py36, py37, py38, pypy, pypy3
 
+[shorthands]
+pip = python {toxinidir}/tools/tox_pip.py
+
 [testenv]
+skip_install = True
+# Environment variables
 passenv = CI GIT_SSL_CAINFO
 setenv =
-    # This is required in order to get UTF-8 output inside of the subprocesses
-    # that our tests use.
+    # Required to get UTF-8 output inside of the subprocesses in tests.
     LC_CTYPE = en_US.UTF-8
+# Use tox_pip.py for when tox runs pip.
+install_command = {[shorthands]pip} install {opts} {packages}
+list_dependencies_command = {[shorthands]pip} freeze
+# The regular stuff
 deps = -r{toxinidir}/tools/tests-requirements.txt
-commands = pytest --timeout 300 []
-install_command = python -m pip install {opts} {packages}
-usedevelop = True
+commands =
+    {[shorthands]pip} install -e {toxinidir}
+    pytest --timeout 300 []
 
 [testenv:coverage-py3]
 basepython = python3
 commands = pytest --timeout 300 --cov=pip --cov-report=term-missing --cov-report=xml --cov-report=html tests/unit {posargs}
 
 [testenv:docs]
-# Don't skip install here since pip_sphinxext uses pip's internals.
 deps = -r{toxinidir}/tools/docs-requirements.txt
 basepython = python2.7
 commands =
+    # Our sphinx extension generates command information, using the installed version
+    {[shorthands]pip} install -e {toxinidir}
+
     sphinx-build -W -d {envtmpdir}/doctrees/html -b html docs/html docs/build/html
     # Having the conf.py in the docs/html is weird but needed because we
     # can not use a different configuration directory vs source directory on RTD
     # currently -- https://github.com/rtfd/readthedocs.org/issues/1543.
-    # That is why we have a "-c docs/html" in the next line.
     sphinx-build -W -d {envtmpdir}/doctrees/man -b man docs/man docs/build/man -c docs/html
 
 [testenv:packaging]
-skip_install = True
 deps =
     check-manifest
     readme_renderer
@@ -46,19 +55,16 @@ commands =
     isort --check-only --diff
 
 [testenv:lint-py2]
-skip_install = True
 basepython = python2
 deps = {[lint]deps}
 commands = {[lint]commands}
 
 [testenv:lint-py3]
-skip_install = True
 basepython = python3
 deps = {[lint]deps}
 commands = {[lint]commands}
 
 [testenv:mypy]
-skip_install = True
 basepython = python3
 deps = mypy
 commands =