Require Flask >= 2.2.0

[jeffwidman]

Require Flask >= 2.2.0.

I'm comfortable going up to requiring 3.x, but when I grep'd for
places we use older Flask constructs, this was all I found.

So for now no need to jump further.

Flask 2.2.0 requires Python >= 3.7, so also dropped older pythons.

I also dropped the Python 3.6 test from being required on the repo branch settings.

Fix #222

[nickjj]

If we're going to drop support for older versions of Flask I do prefer allowing 2.2+ vs 3.0+.

Based on doing a lot of contract work, it may be surprising at how many folks are using older versions of Flask. One of the biggest Flask apps I've worked with (client) is still running 1.1. It has around ~500k lines of Flask / Python code. They use this extension but I think they would be fine sticking with the latest 0.14 release.

One of the orgs I worked with recently was running 2.0 for a long time and recently upgraded to 3.0.

For context:

• Flask 2.0.0 was released on 2021-05-11
• Flask 2.1.0 was released on 2022-03-28
• Flask 2.2.0 was released on 2022-08-01
• Flask 2.3.0 was released on 2023-04-25
• Flask 3.0.0 was released on 2023-09-30

[jeffwidman]

It doesn't surprise me. I've worked in the real world too. 😁

Agree it's a reasonable request, so I switched from 3.0 to 2.2.0 as the minimum.

As a consequence, 2.2.0 requires Python 3.7, so we also drop support for Python 2.7/3.6. IMO that's fine as both have been EOL'd for a while, so anyone still on that old version of Python is unlikely to be updating a small random Flask extension.

[jeffwidman]

Let's hold off on merging this for a few weeks just to ensure our release of the 0.14.x series is stable and we don't encounter more blocker bugs like:

• Add the missing install requirement packaging #225

Also IMO merging this will result in at least a 0.15.0 version bump, possibly higher depending on if we go semver or not.

[nickjj]

Just to give us some confidence, I pulled 0.14.1 into a real Flask 3.0 project and it's all good. There are deprecation warnings to address which should still work with Flask 2.2.0.

[jeffwidman]

Nice, thanks for checking that!

From what I can tell, this PR actually removes all usage of flask.__version__, so merging this will also resolve that deprecation warning.

[macnewbold]

Looks great, and cleans up nicely some things that we won't need.