Re: [Distutils] cffi & Py_LIMITED_API

On 1 August 2016 at 23:36, Daniel Holth wrote:

On Mon, Aug 1, 2016 at 1:42 AM Nick Coghlan wrote:

...

Status quo, on publication side:

- require minimum cffi version 1.8 - build with setuptools - postprocessing step to rename shared library/DLL - postprocessing step to regenerate renamed whl file with renamed SO/DLL

There wouldn't necessarily need to be renaming.

Aye, that description was for the process if there weren't any changes to the toolchain.

build_ext command determines the DLL extension. It could be patched or modified to read an "I'm ABI3" flag on the Extension() object.

We could pass an ABI3 flag to bdist_wheel in the same way we ask for universal 'py2.py3-none-any'. To be set if the wheel contained only ABI3 extensions, and ignored on py2.

The general idea sounds good to me, but as a slight bikeshed on the flag name, perhaps "cpabi3"? That's a mash-up of the 'cp' interpreter code for CPython, with the 'abi3' stable ABI tag. Longer term, we may want to allow people to version that (as new APIs may sometimes be added to the stable ABI, which you gain access to at the C level by setting Py_LIMITED_API to the corresponding CPython hex version rather than just defining it [1]), but as a starting point enabling access to the initial 3.2 stable ABI used by cffi should be sufficient.

...

Of those changes, only the "somehow be Py_LIMITED_API aware" sounds potentially tricky to me, as I'd be surprised if there was any way around requiring a new explicit setting in either setup.py or setup.cfg.

Any alternative to an explicit flag that I can think of would be too magical to consider, as poor as trying to inspect library symbols for manylinux1 compat in bdist_wheel itself.

Aye, that was my conclusion as well. Once my brain started going "Well, we could scan the source for..." I just went "Ewww, no, we can just ask people to set a new flag" :) However, would it make sense for the new flag to also implicitly define Py_LIMITED_API in the compile flags when building the extension, even if it isn't otherwise specified in the extension's source code? That way folks would still only need to define their intent to use the flag in one place, it's just that that place would be their build instructions rather than the extension module source code. Cheers, Nick. [1] https://docs.python.org/3/c-api/stable.html -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia