Add support for free-threaded builds

[hynek]

fixes #67

[hynek]

@tacaswell so I tried to apply @minrk's changes and it's all red: https://github.com/hynek/argon2-cffi-bindings/actions/runs/11229954729

• On Ubuntu, it tries and fails to build a CFFI wheel: https://github.com/hynek/argon2-cffi-bindings/actions/runs/11229954729/job/31216653852 (missing ffi.h!?). This might be possible to fix using cibuildwheel, but I won't bother until the next issue is fixed.

• It seems like cffi is forcing the build into GIL-mode and then our logic to detect free-threading doesn't work and the build fails with "The limited API is not currently supported in the free-threaded build". I have no idea how to work around this?

cc @henryiii

[henryiii]

Can check tomorrow (ping me if I forget), but see python-cffi/cffi#104 in the meantime.

[hynek]

Can check tomorrow (ping me if I forget),

Thanks!

but see python-cffi/cffi#104 in the meantime.

That's rather discouraging and implies the py_limited_api is a NOP? :(

[henryiii]

python-cffi/cffi#125 will be in the next version. Maybe try cffi from git?

[hynek]

python-cffi/cffi#125 will be in the next version. Maybe try cffi from git?

At the danger of embarrassing myself, I have no idea how to do that: pin a git rev in build-requires?

And even worse, I haven't found an easy way to get a free-threaded Python on my Mac? For now, I'm extremely excited for astral-sh/python-build-standalone#336 to ship.

[hynek]

For reference: uv's issue tracking free-threaded installs: astral-sh/uv#8019

[minrk]

pin a git rev in build-requires?

Yeah, you can do that. Perhaps not appropriate for publication, but you can use a git archive URL as a dependency:

[build-system]
requires = [
    "setuptools>=45",
    "setuptools_scm[toml]>=6.2",
    "wheel",
    "cffi>=1.0.1",
    # or a specific commit instead of HEAD
    "https://github.com/python-cffi/cffi/archive/HEAD.tar.gz; python_version >= '3.13'",
]

as done here.

[tacaswell]

Due to changes in setuptools (pypa/setuptools#4647) if you extend bdist_wheel from the wheel package the install will fail. I'm not 100% sure what the support windows of setuptools.wheel is vs the support window that argon2-cff-bindings needs of setuptools so I went with the defensive option. I'll also open a PR against the nogil branch.

diff --git a/setup.py b/setup.py
index 7510937..3a402e3 100644
--- a/setup.py
+++ b/setup.py
@@ -11,9 +11,12 @@ cmdclass = {}

 if platform.python_implementation() == "CPython":
     try:
-        import wheel.bdist_wheel
+        try:
+            from setuptools.command.bdist_wheel import bdist_wheel
+        except ImportError:
+            from wheel.bdist_wheel import bdist_wheel

-        class BDistWheel(wheel.bdist_wheel.bdist_wheel):
+        class BDistWheel(bdist_wheel):
             def finalize_options(self):
                 # Free-threaded CPython doesn't support limited API.
                 if sysconfig.get_config_var("Py_GIL_DISABLED"):
@@ -21,7 +24,7 @@ if platform.python_implementation() == "CPython":
                 else:
                     self.py_limited_api = f"cp3{sys.version_info[1]}"

-                wheel.bdist_wheel.bdist_wheel.finalize_options(self)
+                super().finalize_options()

         cmdclass["bdist_wheel"] = BDistWheel
     except ImportError:

[tacaswell]

The floor on setuptools is 70.1, although I think upstream added a workaround so you can probably ignore my last comment.

[henryiii]

I'd still recommend using the correct one, the workaround is just to keep from blowing up for now, but wheel wants to get rid of it's API long term (it never had a public API, technically).

uv supports free-threaded now.