deprecation: cp313t (#2787)

Free-Threading Python 3.13 was experimental.
Now that Python 3.14 has been released with explicit support, we can schedule removal of Python 3.13 free-threading.

cibuildwheel/__main__.py

@@ -441,11 +441,7 @@ def print_preamble(platform: str, options: Options, identifiers: Sequence[str])
 def detect_errors(*, options: Options, identifiers: Iterable[str]) -> Generator[str, None, None]:
     # Check for deprecated CIBW_FREE_THREADED_SUPPORT environment variable
     if "CIBW_FREE_THREADED_SUPPORT" in os.environ:
-        yield (
-            "CIBW_FREE_THREADED_SUPPORT environment variable is no longer supported. "
-            'Use tool.cibuildwheel.enable = ["cpython-freethreading"] in pyproject.toml '
-            "or set CIBW_ENABLE=cpython-freethreading instead."
-        )
+        yield "CIBW_FREE_THREADED_SUPPORT environment variable is no longer supported."
 
     # Deprecated {python} and {pip}
     for option_name in ["test_command", "before_build"]:
@@ -472,6 +468,13 @@ def detect_warnings(*, options: Options) -> Generator[str, None, None]:
     build_selector = options.globals.build_selector
     test_selector = options.globals.test_selector
 
+    if EnableGroup.CPythonFreeThreading in build_selector.enable:
+        yield (
+            "'cpython-freethreading' enable is deprecated and will be removed in a future version. "
+            "It should be removed from tool.cibuildwheel.enable in pyproject.toml "
+            "or CIBW_ENABLE environment variable."
+        )
+
     all_valid_identifiers = [
         config.identifier
         for module in ALL_PLATFORM_MODULES.values()

cibuildwheel/options.py

@@ -686,6 +686,8 @@ class Options:
             skip_config = ""
             architectures = Architecture.all_archs(self.platform)
             enable |= EnableGroup.all_groups()
+            if args.only.startswith("cp313t-"):
+                enable.add(EnableGroup.CPythonFreeThreading)
 
         build_selector = BuildSelector(
             build_config=build_config,

cibuildwheel/selector.py

@@ -38,7 +38,8 @@ class EnableGroup(StrEnum):
 
     @classmethod
     def all_groups(cls) -> frozenset[Self]:
-        return frozenset(cls)
+        # see https://github.com/python/mypy/issues/20434 for the reason to type: ignore[arg-type]
+        return frozenset(set(cls) - {cls.CPythonFreeThreading})  # type: ignore[arg-type]
 
     @classmethod
     def parse_option_value(cls, value: str) -> frozenset[Self]: