Compile code with Mypyc

[ofek]

Hello again! This is the counterpart to hukkin/tomli#165, without (hopefully?) the bootstrapping concerns 🙂

[hukkin]

Hi ofek, I appreciate the work here!

Unfortunately, I've got another concern. I had a look at hatch-mypyc and it seems it depends on setuptools for building the extension. It seems it creates an ephemeral setup.py and invokes python setup.py build_ext in a subprocess.

Seeing that direct setup.py invocations are deprecated, and the fact that we have to depend on setuptools in the first place, I think I'd prefer to wait for setuptool's PEP 621 support and use setuptools as build backend directly.

[ofek]

Fair enough, just note that unless you know something I don't, the setup.py invocation is unavoidable for using Mypyc/building any extensions.

edit: Does that mean you don't want to use Mypyc?

[hukkin]

Fair enough, just note that unless you know something I don't, the setup.py invocation is unavoidable for using Mypyc/building any extensions.

I probably know less than you. But yeah based on what I read here it seems mypycify is designed as distutils/setuptools only.

The setup.py invocation may be unavoidable, but if so, I'd rather have setuptools itself invoke it as that is the only non-deprecated way to do it.

Does that mean you don't want to use Mypyc?

I like mypyc, but I think I only want it if

• we can stick to PEP 621 metadata
• we don't have to do deprecated setup.py invocations
• mypyc is off-by-default (and mypy is not required in pyproject.toml's build-system.requires). It should be enabled via env variable or other reasonable method.

The ways to achieve this are probably either:

• wait for setuptools's PEP 621 support and use that
• ask mypyc project for a native way for non-setuptools build backends to use it

[hukkin]

Note to self:

If we ever move to using setuptools for mypyc support, the setup.py should look something like this:

import os

from setuptools import setup

if os.environ.get("USE_MYPYC") == "1":
    from mypyc.build import mypycify
    ext_modules = mypycify([
        'src/tomli_w/__init__.py',
        'src/tomli_w/_writer.py',
    ])
else:
    ext_modules = []

setup(ext_modules=ext_modules)