Use vermin to check Python-compat

[WhyNotHugo]

Vermin checks source code for anything that might be incompatible with older Python versions.

This prevents accidentally using a feature from Python 3.10 when we're still supporting 3.8.

While tests ideally detect this, there will always be some bits not covered by tests.

Using a non-release revision since we need some unreleased changes to deal with zoneinfo backports.

See: netromdk/vermin#189

[geier]

Nice.

Seems to work #1276

doesn't catch def test(a: int | str) but does catch 'test'.removeprefix(). Agree, might be helpful.

[netromdk]

Hi there. Vermin author here.

doesn't catch def test(a: int | str) but does catch 'test'.removeprefix(). Agree, might be helpful.

If you are using union types, then you must explicitly enable the detection via --feature union-types. As you can read in the FAQ:

Detecting union types (X | Y PEP 604) can be tricky because Vermin doesn't know all underlying details of constants and types since it parses and traverses the AST. For this reason, heuristics are employed and this can sometimes yield incorrect results (netromdk/vermin#103). To enable (unstable) union types detection, use --feature union-types.

If you have:

def test(a: int | str):
  pass

Then you will get the following using --feature union-types:

!2, 3.10     /tmp/test.py
  L1: annotations require !2, 3.0
  L1: union types as `X | Y` require !2, 3.10

[geier]

Thanks @netromdk for the information!

I was testing basically testing test(a: int | str) because it was the first feature I could think of that python 3.8 doesn't support. I don't think we need to enable that for now.

[netromdk]

Sure thing! :)