- Do not ignore imports which are present and have been added after the
minimum version
- Ignore imports which became mandatory with the minimum version
- Add two older future imports
- Issue an error when a future import does not exist
- Define which is the oldest Python version to be supported so that
already mandatory features can be ignored and not yet supported
features default to forbidden (ignoring the lower error code).
- Use return code of 1 if errors occurred
While this makes things a little more complicated and means we'll need to use
`-r` to recreate tox environments, it has several advantages:
- Full support from requires.io (including PRs)
- Workaround for https://bitbucket.org/hpk42/tox/issues/332/ so we can update
virtualenv/pip
