feat: add option to opt-in free-threaded builds

bin/generate_schema.py

@@ -104,6 +104,10 @@ properties:
     description: Set environment variables on the host to pass-through to the container
       during the build.
     type: string_array
+  free-threaded-support:
+    type: boolean
+    default: false
+    description: The project supports free-threaded builds of Python (PEP703)
   manylinux-aarch64-image:
     type: string
     description: Specify alternative manylinux / musllinux container images
@@ -248,6 +252,7 @@ non_global_options = {k: {"$ref": f"#/properties/{k}"} for k in schema["properti
 del non_global_options["build"]
 del non_global_options["skip"]
 del non_global_options["test-skip"]
+del non_global_options["free-threaded-support"]
 
 overrides["items"]["properties"]["select"]["oneOf"] = string_array
 overrides["items"]["properties"] |= non_global_options.copy()

cibuildwheel/options.py

@@ -117,7 +117,7 @@ class BuildOptions:
         return self.globals.architectures
 
 
-Setting = Union[Mapping[str, str], Sequence[str], str, int]
+Setting = Union[Mapping[str, str], Sequence[str], str, int, bool]
 
 
 @dataclasses.dataclass(frozen=True)
@@ -196,7 +196,7 @@ def _resolve_cascade(
         if value is None:
             continue
 
-        if ignore_empty and not value:
+        if ignore_empty and not value and value is not False:
             continue
 
         value_string = _stringify_setting(value, list_sep, table_format)
@@ -258,7 +258,7 @@ def _stringify_setting(
             raise ConfigOptionError(msg)
         return list_sep.join(setting)
 
-    if isinstance(setting, int):
+    if isinstance(setting, (bool, int)):
         return str(setting)
 
     return setting
@@ -516,6 +516,10 @@ class Options:
         skip_config = self.reader.get("skip", env_plat=False, list_sep=" ")
         test_skip = self.reader.get("test-skip", env_plat=False, list_sep=" ")
 
+        free_threaded_support = strtobool(
+            self.reader.get("free-threaded-support", env_plat=False, ignore_empty=True)
+        )
+
         prerelease_pythons = args.prerelease_pythons or strtobool(
             self.env.get("CIBW_PRERELEASE_PYTHONS", "0")
         )
@@ -536,12 +540,14 @@ class Options:
             skip_config = ""
             architectures = Architecture.all_archs(self.platform)
             prerelease_pythons = True
+            free_threaded_support = True
 
         build_selector = BuildSelector(
             build_config=build_config,
             skip_config=skip_config,
             requires_python=requires_python,
             prerelease_pythons=prerelease_pythons,
+            free_threaded_support=free_threaded_support,
         )
         test_selector = TestSelector(skip_config=test_skip)
 

cibuildwheel/resources/cibuildwheel.schema.json

@@ -255,6 +255,12 @@
       ],
       "title": "CIBW_ENVIRONMENT_PASS"
     },
+    "free-threaded-support": {
+      "type": "boolean",
+      "default": false,
+      "description": "The project supports free-threaded builds of Python (PEP703)",
+      "title": "CIBW_FREE_THREADED_SUPPORT"
+    },
     "manylinux-aarch64-image": {
       "type": "string",
       "description": "Specify alternative manylinux / musllinux container images",

cibuildwheel/resources/defaults.toml

@@ -2,6 +2,7 @@
 build = "*"
 skip = ""
 test-skip = ""
+free-threaded-support = false
 
 archs = ["auto"]
 build-frontend = "default"

cibuildwheel/util.py

@@ -241,6 +241,8 @@ class BuildSelector:
     PRERELEASE_SKIP: ClassVar[str] = "cp313-* cp313t-*"
     prerelease_pythons: bool = False
 
+    free_threaded_support: bool = False
+
     def __call__(self, build_id: str) -> bool:
         # Filter build selectors by python_requires if set
         if self.requires_python is not None:
@@ -257,6 +259,10 @@ class BuildSelector:
         if not self.prerelease_pythons and selector_matches(self.PRERELEASE_SKIP, build_id):
             return False
 
+        # filter out free threaded pythons if self.free_threaded_support is False
+        if not self.free_threaded_support and selector_matches("*t-*", build_id):
+            return False
+
         should_build = selector_matches(self.build_config, build_id)
         should_skip = selector_matches(self.skip_config, build_id)
 
@@ -268,6 +274,7 @@ class BuildSelector:
             "skip_config": self.skip_config,
             "requires_python": str(self.requires_python),
             "prerelease_pythons": self.prerelease_pythons,
+            "free_threaded_support": self.free_threaded_support,
         }
 
 

test/utils.py

@@ -37,6 +37,9 @@ def cibuildwheel_get_build_identifiers(project_path, env=None, *, prerelease_pyt
     cmd = [sys.executable, "-m", "cibuildwheel", "--print-build-identifiers", str(project_path)]
     if prerelease_pythons:
         cmd.append("--prerelease-pythons")
+    if env is None:
+        env = os.environ.copy()
+    env.setdefault("CIBW_FREE_THREADED_SUPPORT", "1")
 
     cmd_output = subprocess.run(
         cmd,
@@ -94,6 +97,8 @@ def cibuildwheel_run(
 
     _update_pip_cache_dir(env)
 
+    env.setdefault("CIBW_FREE_THREADED_SUPPORT", "1")
+
     with TemporaryDirectory() as tmp_output_dir:
         subprocess.run(
             [

unit_test/build_selector_test.py

@@ -50,6 +50,7 @@ def test_build_filter_pre():
     assert build_selector("cp313-manylinux_x86_64")
     assert build_selector("cp37-win_amd64")
     assert build_selector("cp313-win_amd64")
+    assert not build_selector("cp313t-manylinux_x86_64")
 
 
 def test_skip():
@@ -144,6 +145,14 @@ def test_build_limited_python_patch():
     assert build_selector("cp37-manylinux_x86_64")
 
 
+def test_build_free_threaded_python():
+    build_selector = BuildSelector(
+        build_config="*", skip_config="", prerelease_pythons=True, free_threaded_support=True
+    )
+
+    assert build_selector("cp313t-manylinux_x86_64")
+
+
 def test_testing_selector():
     # local import to avoid pytest trying to collect this as a test class!
     from cibuildwheel.util import TestSelector

unit_test/options_test.py

@@ -415,3 +415,36 @@ def test_override_inherit_environment_with_references(tmp_path: Path):
     ) == {
         "PATH": "/opt/local/bin:/opt/bin:/usr/bin:/bin",
     }
+
+
+@pytest.mark.parametrize(
+    ("toml_assignment", "env", "expected_result"),
+    [
+        ("", {}, False),
+        ("free-threaded-support = true", {}, True),
+        ("free-threaded-support = false", {}, False),
+        ("", {"CIBW_FREE_THREADED_SUPPORT": "0"}, False),
+        ("", {"CIBW_FREE_THREADED_SUPPORT": "1"}, True),
+        ("free-threaded-support = false", {"CIBW_FREE_THREADED_SUPPORT": "1"}, True),
+        ("free-threaded-support = true", {"CIBW_FREE_THREADED_SUPPORT": "0"}, False),
+        ("free-threaded-support = true", {"CIBW_FREE_THREADED_SUPPORT": ""}, True),
+        ("free-threaded-support = false", {"CIBW_FREE_THREADED_SUPPORT": ""}, False),
+    ],
+)
+def test_free_threaded_support(
+    tmp_path: Path, toml_assignment: str, env: dict[str, str], expected_result: bool
+):
+    args = CommandLineArguments.defaults()
+    args.package_dir = tmp_path
+
+    pyproject_toml: Path = tmp_path / "pyproject.toml"
+    pyproject_toml.write_text(
+        textwrap.dedent(
+            f"""\
+            [tool.cibuildwheel]
+            {toml_assignment}
+            """
+        )
+    )
+    options = Options(platform="linux", command_line_arguments=args, env=env)
+    assert options.globals.build_selector.free_threaded_support is expected_result