set python to 3.7 in docker container and release action

[remi-delmas-3000]

An attempt to fix a release build issue due to cbmc-viewer depending on voluptuous which now depends on python 3.7 for type annotations.

This adds a ppa in the dockerfile and github release action for ubuntu 18.04 and installs python 3.7.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[feliperodri]

Is there a way to also upgrade the "workaround" for Ubuntu 18.04.

kani/src/os_hacks.rs

Line 53 in d1a038f

pub fn setup_python_deps_on_ubuntu_18_04(pyroot: &Path, pkg_versions: &[&str]) -> Result<()> {

[feliperodri]

We also need to update our dependencies list in the Installation guidelines.

kani/docs/src/install-guide.md

Line 17 in d1a038f

* **Python version 3.6 or newer** and the package installer `pip`.

[remi-delmas-3000]

Is there a way to also upgrade the "workaround" for Ubuntu 18.04.

I am not modifying the OS hacks 18.04 because they are meant to be applied only when the default pip 9.x and python 3.6.x versions are detected on the host. Since we now require python 3.7 they should not have to be applied anymore.

[adpaco-aws]

Since we now require python 3.7 they should not have to be applied anymore.

Why not remove the hacks then?

[remi-delmas-3000]

Why not remove the hacks then?
we would need to add a python version check too

[jaisnan]

Why not remove the hacks then?
we would need to add a python version check too

As discussed offline, I am adding a check for the python version directly, and removing the hacks. @remi-delmas-3000 can you confirm if this is the right plan?

[adpaco-aws]

The Python version checks will abort the installation if the minimum version isn't met. But the setup code isn't expected to do this, what it should do in any case is attempt to solve these problems for you.

[jaisnan]

The Python version checks will abort the installation if the minimum version isn't met. But the setup code isn't expected to do this, what it should do in any case is attempt to solve these problems for you.

I did attempt to solve the problem, but even upgrading to 3.7 is a tough job to accomplish through rust's interface since even python 3.7's reached end-of-life support ☹️. Should we skip 3.7 and directly upgrade the user's python to 3.8 or the latest default version of python?

I assumed the answer to be no, since anyone using python 3.6 or older is likely doing it for very specific reasons, and just informing them seemed like a good idea. Happy to change this behavior, however.

[adpaco-aws]

I assumed the answer to be no, since anyone using python 3.6 or older is likely doing it for very specific reasons, and just informing them seemed like a good idea.

I agree that we shouldn't upgrade python in that case. But here you're not "just informing" the users, you're failing the installation...

Again, why not just remove the hacks? You can leave improvements for later.