ensure-pip: export ensure_pip_virtualenv_command

This makes ensure-pip export something that should be sensible for
users of pip: to put in their 'virtualenv_command' for their host.

The theory of operation is fairly simple; see if "python3 -m venv"
looks like it works, and set that as the command if it does.  If not,
set "virtualenv".  For sanity, we check if it works.

We pull in virtualenv in the Python 2 case, but for Python 3 we are
deliberately do not bring it as it is an unnecessary dependency.  If
jobs do require the actual `virtualenv` package, they should provision
it themselves ... except for Xenial, which, as described inline, has
issues.

Follow-on changes will convert existing zuul-jobs roles that install
tools into virtualenvs to use this argument.

Change-Id: Idad14c0e77eed5bf8df2c8f84f52fbdea2236a9f

roles/ensure-pip/tasks/Debian.yaml

@@ -3,6 +3,7 @@
     name:
       - python3-pip
       - python3-setuptools
+      - python3-venv
   become: yes
 
 - name: Install Python 2 pip

roles/ensure-pip/tasks/RedHat.yaml

@@ -34,6 +34,7 @@
     name:
       - python-pip
       - python-setuptools
+      - python-virtualenv
     state: present
   become: yes
   when: (ensure_pip_from_packages_with_python2) or

roles/ensure-pip/tasks/main.yaml

@@ -29,6 +29,7 @@
 - name: Install pip from packages
   include: "{{ item }}"
   with_first_found:
+    - "{{ ansible_distribution_release }}.yaml"
     - "{{ ansible_distribution }}.yaml"
     - "{{ ansible_os_family }}.yaml"
     - "default.yaml"
@@ -41,3 +42,34 @@
   when:
     - ensure_pip_from_upstream
     - pip_preinstalled.rc != 0
+
+#
+# virtualenv setup
+#
+- name: Probe for venv
+  command: /usr/bin/python3 -m venv --help
+  no_log: True
+  failed_when: false
+  register: _venv_probe
+
+- name: Set host default
+  set_fact:
+    _host_virtualenv: '{{ (_venv_probe.rc == 0) | ternary("/usr/bin/python3 -m venv", "virtualenv") }}'
+  when: ansible_distribution_release != 'xenial'
+
+# The pip included with Xenial (version ~8) has issues with our wheel
+# mirrors; it will not correctly look to upstream pypi when it can't
+# find the wheel in the configured mirror, so virutalenv creation
+# fails.  venv uses the system pip version; for this reason we need to
+# use virtualenv which does upgrade pip in the environment; but note
+# that on Xenial "virtualenv" is owned by the python2 package; so we
+# specify the command to python3 directly.
+- name: Set host default (Xenial)
+  set_fact:
+    _host_virtualenv: '/usr/bin/python3 -m virtualenv'
+  when: ansible_distribution_release == 'xenial'
+
+- name: Set ensure_pip_virtualenv_cmd
+  set_fact:
+    ensure_pip_virtualenv_command: '{{ ensure_pip_virtualenv_command | default(_host_virtualenv) }}'
+    cacheable: true

roles/ensure-pip/tasks/xenial.yaml

@@ -0,0 +1,20 @@
+# See notes in main.yaml about the virtualenv requirements
+
+- name: Install Python 3 pip
+  package:
+    name:
+      - python3-pip
+      - python3-setuptools
+      - python3-venv
+      - python3-virtualenv
+  become: yes
+
+- name: Install Python 2 pip
+  package:
+    name:
+      - python-setuptools
+      - python-pip
+      - python-virtualenv
+  become: yes
+  when: (ensure_pip_from_packages_with_python2) or
+        (ansible_python.version.major == 2)

test-playbooks/ensure-pip.yaml

@@ -1,6 +1,21 @@
 - hosts: all
   roles:
     - ensure-pip
+  tasks:
+    - name: Sanity check provided virtualenv command works
+      shell: |
+        tmp_venv=$(mktemp -d -t venv-XXXXXXXXXX)
+        trap "rm -rf $tmp_venv" EXIT
+        {{ ensure_pip_virtualenv_command }} $tmp_venv
+        $tmp_venv/bin/pip install tox
+      failed_when: false
+      register: _venv_sanity
+
+    - name: Assert sanity check
+      fail:
+        msg: 'The virtualenv_command: "{{ ensure_pip_virtualenv_command }}" does not appear to work!'
+      when:
+        - _venv_sanity.rc != 0
 
 # NOTE(ianw) : this does not play nicely with pip-and-virtualenv which
 # has already installed from source.  We might be able to test this