Fix free-threaded Python 3.14t compilation and thread safety

.github/workflows/tests.yml

@@ -99,6 +99,9 @@ jobs:
         exclude:
           - os: macos-latest
             python-version: "pypy-3.11"
+        include:
+          - python-version: "3.14t"
+            os: ubuntu-latest
 
     steps:
       - name: checkout
@@ -255,6 +258,9 @@ jobs:
         exclude:
           - os: macos-latest
             python-version: "pypy-3.11"
+        include:
+          - python-version: "3.14t"
+            os: ubuntu-latest
 
     steps:
       - name: checkout
@@ -561,7 +567,7 @@ jobs:
           # PyPy wheels shouldn't be uploaded, remove them if present
           find dist/ -name "*pypy*" -type f -delete || true
           find dist/ -name "*none-any*" -type f -delete || true
-          # Wheels for the no-yet-supported future Python version need to go
+          # Wheels for the not-yet-supported future Python version need to go
           find dist/ -name "*3.15*" -type f -delete || true
           find dist/ -name "*cp315*" -type f -delete || true
           # For Linux, we only want the manylinux wheels

.gitignore

@@ -28,5 +28,6 @@ lib64
 log/
 parts/
 pyvenv.cfg
+share/
 testing.log
 var/

.meta.toml

@@ -2,7 +2,7 @@
 # https://github.com/zopefoundation/meta/tree/master/src/zope/meta/c-code
 [meta]
 template = "c-code"
-commit-id = "f62d8bab"
+commit-id = "2dc4f53b"
 
 [python]
 with-windows = true
@@ -11,6 +11,7 @@ with-sphinx-doctests = false
 with-future-python = true
 with-macos = false
 with-docs = false
+with-free-threaded-python = true
 
 [coverage]
 fail-under = 99.5

.pre-commit-config.yaml

@@ -12,7 +12,7 @@ repos:
     - id: autopep8
       args: [--in-place, --aggressive, --aggressive]
   - repo: https://github.com/asottile/pyupgrade
-    rev: v3.21.0
+    rev: v3.21.2
     hooks:
     - id: pyupgrade
       args: [--py310-plus]

CHANGES.rst

@@ -4,6 +4,12 @@ Change log
 6.3 (unreleased)
 ----------------
 
+- Fix compilation on free-threaded Python 3.14t: use ``Py_REFCNT()`` macro
+  instead of direct ``ob_refcnt`` struct access, guard ``im_self`` mutation
+  optimization with ``#ifndef Py_GIL_DISABLED``.
+
+- Add CI testing for free-threaded Python 3.14t (Linux).
+
 
 6.2 (2025-11-16)
 ----------------

src/ExtensionClass/_ExtensionClass.c

@@ -884,17 +884,20 @@ PyECMethod_New_(PyObject *callable, PyObject *inst)
 
   if (PyMethod_Check(callable))
     {
-      if (callable->ob_refcnt == 1)
+#ifndef Py_GIL_DISABLED
+      if (Py_REFCNT(callable) == 1)
         {
+          /* Optimization: reuse the method object when we have exclusive
+             ownership.  Not safe in the free-threaded build because another
+             thread could observe the mutation of im_self. */
           Py_XDECREF(((PyMethodObject*)callable)->im_self);
           Py_INCREF(inst);
           ((PyMethodObject*)callable)->im_self = inst;
           Py_INCREF(callable);
           return callable;
         }
-      else {
-            return PyMethod_New(PyMethod_GET_FUNCTION(callable), inst);
-      }
+#endif
+      return PyMethod_New(PyMethod_GET_FUNCTION(callable), inst);
     }
   else {
         return PyMethod_New(callable, inst);

tox.ini

@@ -11,6 +11,7 @@ envlist =
     py313,py313-pure
     py314,py314-pure
     py315,py315-pure
+    py314t,py314t-pure
     pypy3
     coverage
 
@@ -60,7 +61,7 @@ deps =
 commands_pre =
 commands =
     check-manifest
-    check-python-versions --only pyproject.toml,setup.py,tox.ini,.github/workflows/tests.yml
+    check-python-versions --only pyproject.toml,setup.py,tox.ini
     python -m build --sdist --no-isolation
     twine check dist/*