pytest not found causing build to fail

[mikaelarguedas]

similar to osrf/docker_images#270

This seem to be due to an issue when different version of pytest and plugins are installed from both apt and pip .

Workaround: Installing colcon from pip and not from apt seems to work around the issue

Bug report

Required Info:

• Operating System:
  • Ubuntu bionic
• Installation type:
  • source and nightly archives
• Version or commit hash:
  • dashing-release
• DDS implementation:
  • N/A
• Client library (if applicable):
  • N/A

Steps to reproduce issue

docker run -it --rm ubuntu:bionic
mkdir -p ~/ros2_install
cd ~/ros2_install
apt -qq update && apt -qq upgrade -y && apt -qq install -y curl gnupg2 lsb-release
curl http://repo.ros2.org/repos.key | apt-key add -
sh -c 'echo "deb [arch=amd64,arm64] http://packages.ros.org/ros2/ubuntu `lsb_release -cs` main" > /etc/apt/sources.list.d/ros2-latest.list'
echo 'Etc/UTC' > /etc/timezone && \
    ln -s /usr/share/zoneinfo/Etc/UTC /etc/localtime
apt -qq update && apt install -y   build-essential   cmake   git   python3-colcon-common-extensions   python3-lark-parser   python3-lxml   python3-numpy   python3-pip   python-rosdep   python3-vcstool   wget
python3 -m pytest --version

This works and displays

This is pytest version 3.3.2, imported from /usr/lib/python3/dist-packages/pytest.py
setuptools registered plugins:
  pytest-cov-2.5.1 at /usr/lib/python3/dist-packages/pytest_cov/plugin.py

Installing pytest plugins from pip as per ROS2 documentation:

python3 -m pip install -U   argcomplete   flake8   flake8-blind-except   flake8-builtins   flake8-class-newline   flake8-comprehensions   flake8-deprecated   flake8-docstrings   flake8-import-order   flake8-quotes   pytest-repeat   pytest-rerunfailures
python3 -m pytest --version

This fails

Also installing pytest plugins that were in the xenial section and are now in the bionic section:

python3 -m pip install -U   pytest   pytest-cov   pytest-runner   setuptools
python3 -m pytest --version

This still fails

Removing colcon and unused dependencies fixes the issue

apt remove python3-colcon-common-extensions && apt autoremove
python3 -m pytest --version

Reinstalling colcon from pip, it still works

python3 -m pip install colcon-common-extensions
python3 -m pytest --version

Expected behavior

python3 -m pytest --version still works after installing colcon

Actual behavior

Error message

Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.6/dist-packages/pytest.py", line 102, in <module>
    raise SystemExit(pytest.main())
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 63, in main
    config = _prepareconfig(args, plugins)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 207, in _prepareconfig
    pluginmanager=pluginmanager, args=args
  File "/usr/local/lib/python3.6/dist-packages/pluggy/hooks.py", line 289, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/usr/local/lib/python3.6/dist-packages/pluggy/manager.py", line 87, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/usr/local/lib/python3.6/dist-packages/pluggy/manager.py", line 81, in <lambda>
    firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
  File "/usr/local/lib/python3.6/dist-packages/pluggy/callers.py", line 203, in _multicall
    gen.send(outcome)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/helpconfig.py", line 94, in pytest_cmdline_parse
    config = outcome.get_result()
  File "/usr/local/lib/python3.6/dist-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/usr/local/lib/python3.6/dist-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 687, in pytest_cmdline_parse
    self.parse(args)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 895, in parse
    self._preparse(args, addopts=addopts)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 836, in _preparse
    self._consider_importhook(args)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 784, in _consider_importhook
    self._mark_plugins_for_rewrite(hook)
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 806, in _mark_plugins_for_rewrite
    for name in _iter_rewritable_modules(package_files):
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 625, in _iter_rewritable_modules
    for fn in package_files:
  File "/usr/local/lib/python3.6/dist-packages/_pytest/config/__init__.py", line 803, in <genexpr>
    for file in dist.files
TypeError: 'NoneType' object is not iterable

Additional information

[dirk-thomas]

Duplicate of ros2/ros2_documentation#271.