add a pp3-none-any tag

[mattip]

Closes #311. Now that this project is used by pip and wheel, the discussion there about where to make the change is less relevant, I hope that reading the description below convinces the maintainers that the change is justified.

This inserts a pp3-none-any tag as the first any-platform tag.

This subject came up again for the vmprof project, which is a statistical profiler for cpython/pypy. The project has two parts: a pure-python front end, and a backend. On CPython, the backend is a c-extension module. On PyPy, the backend is built into the interpreter and understands the JIT. So when making wheels for the project, we want c-extension binary wheels for CPython and a pure-python wheel for PyPy.

Here is a snippet of the output of tags.sys_tags() using PyPy 3.7 on ubuntu 20.04/x86_64.

...
 <py30-none-manylinux_2_7_x86_64 @ 140603724368544>,
 <py30-none-manylinux_2_6_x86_64 @ 140603724368600>,
 <py30-none-manylinux_2_5_x86_64 @ 140603724368656>,
 <py30-none-manylinux1_x86_64 @ 140603724368712>,
 <py30-none-linux_x86_64 @ 140603724368768>,
 <pp3-none-any @ 140603724368824>,    # <---------- here
 <py37-none-any @ 140603724368880>,
 <py3-none-any @ 140603724368936>,
 <py36-none-any @ 140603724369440>,
 <py35-none-any @ 140603724369496>,
 <py34-none-any @ 140603724369552>,
...

[mattip]

Rebased to pull in #467

[brettcannon]

Won't this affect PyPy 2's tags since it's hard-coded to pp3? Or is that not a concern?

[mattip]

Won't this affect PyPy 2's tags since it's hard-coded to pp3?

I think the trove classifier specifies "Programming Language :: Python :: 3 :: Only" so python2 is not relevant, correct?

[brettcannon]

I'm thinking from a tag perspective. If I'm reading the code right, the logic right now only checks if the interpreter type is pp, and if it is it then adds the proposed pp3-none-any triple. But what about if the interpreter is PyPy 2? There's no way for that tag to be legitimate in that case, so I'm trying to figure out if the current logic is too lax/simple by not checking the interpreter version.

[mattip]

But what about if the interpreter is PyPy 2?

The code cannot be called by pypy2, it errors out on the typing sytax

packaging/packaging/tags.py

Line 30 in 42e1396

INTERPRETER_SHORT_NAMES: Dict[str, str] = {

[brettcannon]

LGTM; just waiting on CI after fast-forwarding to the latest on main.