feat: add CPython 3.15 support for iOS (#2857)

* feat: add CPython 3.15 support for iOS

Assisted-by: OpenCode:Kimi-K2.6
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: copy in iOS support files

Assisted-by: Copilot:claude-sonnet-4.6
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: skip directories when copying iOS support files

When copying multiarch-specific support files (e.g. _cross_arm64_iphoneos.py),
the code was trying to copy all items in the directory including __pycache__
directories. The shutil.copy() function only works with files, not directories,
which caused an IsADirectoryError.

This fix adds a check to only copy files, skipping any directories like
__pycache__ that may have been created by Python imports.

Assisted-by: Copilot:claude-haiku-4.5

* fix: - in dir fine for now

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: apply review suggestions

Assisted-by: Copilot:claude-sonnet-4.6
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* fix: only do this on 3.15+

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* Ensure target Python directory exists before build

Add assertion to check if target Python directory exists.

* fix(ios): use stdlib dir directly instead of copying to platform-config

Remove the _inject_support_files workaround for python.org 3.15+
distributions. Instead of copying sysconfig files from the stdlib into
a synthetic platform-config/ directory, pass the stdlib directory
directly to make_cross_venv.py.

make_cross_venv.py is updated to derive the multiarch tag from the
_sysconfigdata_ filename rather than assuming it comes from the
directory name.

Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>
Assisted-by: OpenCode:Kimi-K2.6
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

* Minor format cleanups on pre-commit skipped files.

* Clarify path names in make_cross_venv script.

---------

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>

.pre-commit-config.yaml

@@ -1,5 +1,6 @@
 ci:
   autoupdate_schedule: monthly
+exclude: "^cibuildwheel/resources/ios-support/(?!make_cross_venv\\.py)"
 
 repos:
 - repo: https://github.com/pre-commit/pre-commit-hooks

README.md

@@ -24,13 +24,13 @@ While cibuildwheel itself requires a recent Python version to run (we support th
 
 |                          | macOS Intel | macOS Apple Silicon | Windows 64bit | Windows 32bit | Windows Arm64  | manylinux<br/>musllinux x86_64 | manylinux<br/>musllinux i686 | manylinux<br/>musllinux aarch64 | manylinux<br/>musllinux ppc64le | manylinux<br/>musllinux s390x | manylinux<br/>musllinux armv7l | Android | iOS | Pyodide        |
 | ------------------------ | ----------- | ------------------- | ------------- | ------------- | -------------- | ------------------------------ | ---------------------------- | ------------------------------- | ------------------------------- | ----------------------------- | ------------------------------ | ------- | --- | -------------- |
-| CPython 3.9              | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | N/A            |
+| CPython 3.9              | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | N/A            |
-| CPython 3.10             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | N/A            |
+| CPython 3.10             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | N/A            |
-| CPython 3.11             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | N/A            |
+| CPython 3.11             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | N/A            |
-| CPython 3.12             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | ✅<sup>3</sup> |
+| CPython 3.12             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | N/A     | N/A | ✅<sup>3</sup> |
-| CPython 3.13             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | ✅      | ✅  | ✅             |
+| CPython 3.13             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | ✅      | ✅  | ✅             |
-| CPython 3.14             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | ✅      | ✅  | ✅<sup>4</sup> |
+| CPython 3.14             | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | ✅      | ✅  | ✅<sup>4</sup> |
-| CPython 3.15<sup>6</sup> | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | ✅      | N/A | N/A            |
+| CPython 3.15<sup>6</sup> | ✅          | ✅                  | ✅            | ✅            | ✅<sup>2</sup> | ✅                             | ✅                           | ✅                              | ✅                              | ✅                            | ✅<sup>5</sup>                 | ✅      | ✅  | N/A            |
 | PyPy 3.9 v7.3            | ✅          | ✅                  | ✅            | N/A           | N/A            | ✅<sup>1</sup>                 | ✅<sup>1</sup>               | ✅<sup>1</sup>                  | N/A                             | N/A                           | N/A                            | N/A     | N/A | N/A            |
 | PyPy 3.10 v7.3           | ✅          | ✅                  | ✅            | N/A           | N/A            | ✅<sup>1</sup>                 | ✅<sup>1</sup>               | ✅<sup>1</sup>                  | N/A                             | N/A                           | N/A                            | N/A     | N/A | N/A            |
 | PyPy 3.11 v7.3           | ✅          | ✅                  | ✅            | N/A           | N/A            | ✅<sup>1</sup>                 | ✅<sup>1</sup>               | ✅<sup>1</sup>                  | N/A                             | N/A                           | N/A                            | N/A     | N/A | N/A            |

bin/update_pythons.py

@@ -488,7 +488,14 @@ class AllVersions:
             versions = self.maven if identifier.startswith("cp313") else self.cpython
             config_update = versions.update_version_android(identifier, spec)
         elif "ios" in identifier:
+            # Python 3.13 and 3.14 are released by BeeWare on GitHub.
+            # Python 3.15 and newer have official releases on python.org.
+            if identifier.startswith(("cp313", "cp314")):
                 config_update = self.ios_cpython.update_version_ios(identifier, version)
+            else:
+                config_update = self.cpython.update_version(
+                    identifier, spec, "iOS-XCframework.tar.gz"
+                )
         elif "pyodide" in identifier:
             config_update = self.pyodide.update_version_pyodide(
                 identifier, version, spec, config["node_version"]

cibuildwheel/platforms/ios.py

@@ -11,6 +11,7 @@ from pathlib import Path
 from typing import assert_never
 
 from filelock import FileLock
+from packaging.version import Version
 
 from cibuildwheel import errors
 from cibuildwheel.architecture import Architecture
@@ -183,14 +184,33 @@ def cross_virtualenv(
     )
 
     # Convert the macOS virtual environment into an iOS virtual environment
-    # using the cross-platform conversion script in the iOS distribution.
+    # using make_cross_venv.py.
 
     # target_python is the path to the Python binary;
     # determine the root of the XCframework slice that is being used.
     slice_path = target_python.parent.parent
+    if Version(py_version) >= Version("3.15"):
+        # python.org 3.15+ distributions: sysconfig data lives in the
+        # stdlib directory (lib-<arch>/python<version>); cross-venv scripts
+        # come from cibuildwheel resources.
+        arch = multiarch.split("-", maxsplit=1)[0]
+        stdlib_path = slice_path / f"lib-{arch}" / f"python{py_version}"
         call(
             "python",
-        str(slice_path / f"platform-config/{multiarch}/make_cross_venv.py"),
+            str(resources.IOS_SUPPORT_FILES / "make_cross_venv.py"),
+            str(venv_path),
+            str(stdlib_path),
+            str(resources.IOS_SUPPORT_FILES),
+            env=env,
+            cwd=venv_path,
+        )
+    else:
+        # BeeWare distributions: platform-config already contains both
+        # sysconfig data and the make_cross_venv.py script.
+        platform_config_path = slice_path / f"platform-config/{multiarch}"
+        call(
+            "python",
+            str(platform_config_path / "make_cross_venv.py"),
             str(venv_path),
             env=env,
             cwd=venv_path,
@@ -312,8 +332,8 @@ def setup_python(
         / f"python{python_configuration.version}"
     )
 
-    assert target_python.exists(), (
+    assert target_python.parent.exists(), (
-        f"{target_python.name} not found, has {list(target_install_path.iterdir())}"
+        f"{target_python.parent} not found, has {list(target_install_path.iterdir())}"
     )
 
     log.step("Creating cross build environment...")

cibuildwheel/resources/build-platforms.toml

@@ -243,4 +243,7 @@ python_configurations = [
   { identifier = "cp314-ios_arm64_iphoneos", version = "3.14", url = "https://github.com/beeware/Python-Apple-support/releases/download/3.14-b9/Python-3.14-iOS-support.b9.tar.gz" },
   { identifier = "cp314-ios_x86_64_iphonesimulator", version = "3.14", url = "https://github.com/beeware/Python-Apple-support/releases/download/3.14-b9/Python-3.14-iOS-support.b9.tar.gz" },
   { identifier = "cp314-ios_arm64_iphonesimulator", version = "3.14", url = "https://github.com/beeware/Python-Apple-support/releases/download/3.14-b9/Python-3.14-iOS-support.b9.tar.gz" },
+  { identifier = "cp315-ios_arm64_iphoneos", version = "3.15", url = "https://www.python.org/ftp/python/3.15.0/python-3.15.0b1-iOS-XCframework.tar.gz" },
+  { identifier = "cp315-ios_x86_64_iphonesimulator", version = "3.15", url = "https://www.python.org/ftp/python/3.15.0/python-3.15.0b1-iOS-XCframework.tar.gz" },
+  { identifier = "cp315-ios_arm64_iphonesimulator", version = "3.15", url = "https://www.python.org/ftp/python/3.15.0/python-3.15.0b1-iOS-XCframework.tar.gz" },
 ]

cibuildwheel/resources/ios-support/_cross_venv.py

@@ -0,0 +1,103 @@
+import shutil
+import sys
+import sysconfig
+from pathlib import Path
+
+SITE_PACKAGE_PATH = Path(__file__).parent
+
+###########################################################################
+# importlib module patches
+###########################################################################
+
+
+def patch_env_create(env):
+    """
+    Patch the process of creating virtual environments to ensure that the cross
+    environment modification files are also copied as part of environment
+    creation.
+    """
+    old_pip_env_create = env._PipBackend.create
+
+    def pip_env_create(self, path, *args, **kwargs):
+        result = old_pip_env_create(self, path, *args, **kwargs)
+        # Copy any _cross_*.pth or _cross_*.py file, plus the cross-platform
+        # sysconfigdata module and sysconfig_vars JSON to the new environment.
+        data_name = sysconfig._get_sysconfigdata_name()
+        json_name = data_name.replace("_sysconfigdata", "_sysconfig_vars")
+        for filename in [
+            "_cross_venv.pth",
+            "_cross_venv.py",
+            f"_cross_{sys.implementation._multiarch.replace('-', '_')}.py",
+            f"{data_name}.py",
+            f"{json_name}.json",
+        ]:
+            src = SITE_PACKAGE_PATH / filename
+            target = Path(path) / src.relative_to(SITE_PACKAGE_PATH.parent.parent.parent)
+            if not target.exists():
+                shutil.copy(src, target)
+        return result
+
+    env._PipBackend.create = pip_env_create
+
+
+# Import hook that patches the creation of virtual environments by `build`
+#
+# The approach used here is the same as the one used by virtualenv to patch
+# distutils (but without support for the older load_module API).
+# https://docs.python.org/3/library/importlib.html#setting-up-an-importer
+_BUILD_PATCH = ("build.env",)
+
+
+class _Finder:
+    """A meta path finder that allows patching the imported build modules."""
+
+    fullname = None
+
+    # lock[0] is threading.Lock(), but initialized lazily to avoid importing
+    # threading very early at startup, because there are gevent-based
+    # applications that need to be first to import threading by themselves.
+    # See https://github.com/pypa/virtualenv/issues/1895 for details.
+    lock = []  # noqa: RUF012
+
+    def find_spec(self, fullname, path, target=None):
+        if fullname in _BUILD_PATCH and self.fullname is None:
+            # initialize lock[0] lazily
+            if len(self.lock) == 0:
+                import threading
+
+                lock = threading.Lock()
+                # there is possibility that two threads T1 and T2 are
+                # simultaneously running into find_spec, observing .lock as
+                # empty, and further going into hereby initialization. However
+                # due to the GIL, list.append() operation is atomic and this
+                # way only one of the threads will "win" to put the lock
+                # - that every thread will use - into .lock[0].
+                # https://docs.python.org/3/faq/library.html#what-kinds-of-global-value-mutation-are-thread-safe
+                self.lock.append(lock)
+
+            from functools import partial
+            from importlib.util import find_spec
+
+            with self.lock[0]:
+                self.fullname = fullname
+                try:
+                    spec = find_spec(fullname, path)
+                    if spec is not None:
+                        # https://www.python.org/dev/peps/pep-0451/#how-loading-will-work
+                        old = spec.loader.exec_module
+                        func = self.exec_module
+                        if old is not func:
+                            spec.loader.exec_module = partial(func, old)
+                        return spec
+                finally:
+                    self.fullname = None
+        return None
+
+    @staticmethod
+    def exec_module(old, module):
+        old(module)
+        if module.__name__ in _BUILD_PATCH:
+            patch_env_create(module)
+
+
+sys.meta_path.insert(0, _Finder())

cibuildwheel/resources/ios-support/arm64-iphoneos/_cross_arm64_iphoneos.py

@@ -0,0 +1,79 @@
+# A site package that turns a macOS virtual environment
+# into an arm64 iphoneos cross-platform virtual environment
+import platform
+import subprocess
+import sys
+import sysconfig
+
+###########################################################################
+# sys module patches
+###########################################################################
+sys.cross_compiling = True
+sys.platform = "ios"
+sys.implementation._multiarch = "arm64-iphoneos"
+sys.base_prefix = sysconfig._get_sysconfigdata()["prefix"]
+sys.base_exec_prefix = sysconfig._get_sysconfigdata()["prefix"]
+
+###########################################################################
+# subprocess module patches
+###########################################################################
+subprocess._can_fork_exec = True
+
+
+###########################################################################
+# platform module patches
+###########################################################################
+
+
+def cross_system():
+    return "iOS"
+
+
+def cross_uname():
+    return platform.uname_result(
+        system="iOS",
+        node="build",
+        release="13.0",
+        version="",
+        machine="arm64",
+    )
+
+
+def cross_ios_ver(system="", release="", model="", is_simulator=False):
+    if system == "":
+        system = "iOS"
+    if release == "":
+        release = "13.0"
+    if model == "":
+        model = "iphoneos"
+
+    return platform.IOSVersionInfo(system, release, model, False)
+
+
+platform.system = cross_system
+platform.uname = cross_uname
+platform.ios_ver = cross_ios_ver
+
+
+###########################################################################
+# sysconfig module patches
+###########################################################################
+
+
+def cross_get_platform():
+    return "ios-13.0-arm64-iphoneos"
+
+
+def cross_get_sysconfigdata_name():
+    return "_sysconfigdata__ios_arm64-iphoneos"
+
+
+sysconfig.get_platform = cross_get_platform
+sysconfig._get_sysconfigdata_name = cross_get_sysconfigdata_name
+
+# Ensure module-level values cached at time of import are updated.
+sysconfig._BASE_PREFIX = sys.base_prefix
+sysconfig._BASE_EXEC_PREFIX = sys.base_exec_prefix
+
+# Force sysconfig data to be loaded (and cached).
+sysconfig._init_config_vars()

cibuildwheel/resources/ios-support/arm64-iphoneos/sitecustomize.py

@@ -0,0 +1,22 @@
+# A site customization that can be used to trick pip into installing packages
+# cross-platform. If the folder containing this file is on your PYTHONPATH when
+# you invoke python, the interpreter will behave as if it were running on
+# arm64 iphoneos.
+import sys
+import os
+
+# Apply the cross-platform patch
+import _cross_arm64_iphoneos
+import _cross_venv
+
+
+# Call the next sitecustomize script if there is one
+# (https://nedbatchelder.com/blog/201001/running_code_at_python_startup.html).
+del sys.modules["sitecustomize"]
+this_dir = os.path.dirname(__file__)
+path_index = sys.path.index(this_dir)
+del sys.path[path_index]
+try:
+    import sitecustomize  # noqa: F401
+finally:
+    sys.path.insert(path_index, this_dir)

cibuildwheel/resources/ios-support/arm64-iphonesimulator/_cross_arm64_iphonesimulator.py

@@ -0,0 +1,79 @@
+# A site package that turns a macOS virtual environment
+# into an arm64 iphonesimulator cross-platform virtual environment
+import platform
+import subprocess
+import sys
+import sysconfig
+
+###########################################################################
+# sys module patches
+###########################################################################
+sys.cross_compiling = True
+sys.platform = "ios"
+sys.implementation._multiarch = "arm64-iphonesimulator"
+sys.base_prefix = sysconfig._get_sysconfigdata()["prefix"]
+sys.base_exec_prefix = sysconfig._get_sysconfigdata()["prefix"]
+
+###########################################################################
+# subprocess module patches
+###########################################################################
+subprocess._can_fork_exec = True
+
+
+###########################################################################
+# platform module patches
+###########################################################################
+
+
+def cross_system():
+    return "iOS"
+
+
+def cross_uname():
+    return platform.uname_result(
+        system="iOS",
+        node="build",
+        release="13.0",
+        version="",
+        machine="arm64",
+    )
+
+
+def cross_ios_ver(system="", release="", model="", is_simulator=False):
+    if system == "":
+        system = "iOS"
+    if release == "":
+        release = "13.0"
+    if model == "":
+        model = "iphonesimulator"
+
+    return platform.IOSVersionInfo(system, release, model, True)
+
+
+platform.system = cross_system
+platform.uname = cross_uname
+platform.ios_ver = cross_ios_ver
+
+
+###########################################################################
+# sysconfig module patches
+###########################################################################
+
+
+def cross_get_platform():
+    return "ios-13.0-arm64-iphonesimulator"
+
+
+def cross_get_sysconfigdata_name():
+    return "_sysconfigdata__ios_arm64-iphonesimulator"
+
+
+sysconfig.get_platform = cross_get_platform
+sysconfig._get_sysconfigdata_name = cross_get_sysconfigdata_name
+
+# Ensure module-level values cached at time of import are updated.
+sysconfig._BASE_PREFIX = sys.base_prefix
+sysconfig._BASE_EXEC_PREFIX = sys.base_exec_prefix
+
+# Force sysconfig data to be loaded (and cached).
+sysconfig._init_config_vars()

cibuildwheel/resources/ios-support/arm64-iphonesimulator/sitecustomize.py

@@ -0,0 +1,22 @@
+# A site customization that can be used to trick pip into installing packages
+# cross-platform. If the folder containing this file is on your PYTHONPATH when
+# you invoke python, the interpreter will behave as if it were running on
+# arm64 iphonesimulator.
+import sys
+import os
+
+# Apply the cross-platform patch
+import _cross_arm64_iphonesimulator
+import _cross_venv
+
+
+# Call the next sitecustomize script if there is one
+# (https://nedbatchelder.com/blog/201001/running_code_at_python_startup.html).
+del sys.modules["sitecustomize"]
+this_dir = os.path.dirname(__file__)
+path_index = sys.path.index(this_dir)
+del sys.path[path_index]
+try:
+    import sitecustomize  # noqa: F401
+finally:
+    sys.path.insert(path_index, this_dir)

cibuildwheel/resources/ios-support/make_cross_venv.py

@@ -0,0 +1,175 @@
+from __future__ import annotations
+
+import json
+import pprint
+import shutil
+import sys
+from importlib import util as importlib_util
+from pathlib import Path
+from typing import Any
+
+
+def localized_vars(orig_vars: dict[str, Any], slice_path: Path) -> dict[str, Any]:
+    """Update (where possible) any references to build-time variables with the
+    best guess of the installed location.
+    """
+    # The host's sysconfigdata will include references to build-time variables.
+    # Update these to refer to the current known install location.
+    orig_prefix = orig_vars["prefix"]
+    localized_vars = {}
+    for key, value in orig_vars.items():
+        final = value
+        if isinstance(value, str):
+            # Replace any reference to the build installation prefix
+            final = final.replace(orig_prefix, str(slice_path))
+            # Replace any reference to the build-time Framework location
+            final = final.replace("-F .", f"-F {slice_path}")
+        localized_vars[key] = final
+
+    return localized_vars
+
+
+def localize_sysconfigdata(sysconfig_path: Path, venv_site_packages: Path) -> None:
+    """Localize a sysconfigdata python module.
+
+    :param sysconfig_path: The platform config that contains the
+        sysconfigdata module to localize.
+    :param venv_site_packages: The site packages folder where the localized
+        sysconfigdata module should be output.
+    """
+    # Find the "_sysconfigdata_*.py" file in the platform config
+    sysconfigdata_path = next(sysconfig_path.glob("_sysconfigdata_*.py"))
+
+    # Import the sysconfigdata module
+    spec = importlib_util.spec_from_file_location(sysconfigdata_path.stem, sysconfigdata_path)
+    if spec is None:
+        msg = f"Unable to load spec for {sysconfigdata_path}"
+        raise ValueError(msg)
+    if spec.loader is None:
+        msg = f"Spec for {sysconfigdata_path} does not define a loader"
+        raise ValueError(msg)
+    sysconfigdata = importlib_util.module_from_spec(spec)
+    spec.loader.exec_module(sysconfigdata)
+
+    # Write the updated sysconfigdata module into the cross-platform site.
+    slice_path = sysconfigdata_path.parent.parent.parent
+    with (venv_site_packages / sysconfigdata_path.name).open("w") as f:
+        f.write(f"# Generated from {sysconfigdata_path}\n")
+        f.write("build_time_vars = ")
+        pprint.pprint(
+            localized_vars(sysconfigdata.build_time_vars, slice_path), stream=f, compact=True
+        )
+
+
+def localize_sysconfig_vars(sysconfig_path: Path, venv_site_packages: Path) -> None:
+    """Localize a sysconfig_vars.json file.
+
+    :param sysconfig_path: The platform config that contains the
+        sysconfigdata module to localize.
+    :param venv_site_packages: The site-packages folder where the localized
+        sysconfig_vars.json file should be output.
+    """
+    # Find the "_sysconfig_vars_*.json" file in the platform config
+    sysconfig_vars_path = next(sysconfig_path.glob("_sysconfig_vars_*.json"))
+
+    with sysconfig_vars_path.open("rb") as f:
+        build_time_vars = json.load(f)
+
+    slice_path = sysconfig_vars_path.parent.parent.parent
+    with (venv_site_packages / sysconfig_vars_path.name).open("w") as f:
+        json.dump(localized_vars(build_time_vars, slice_path), f, indent=2)
+
+
+def make_cross_venv(
+    venv_path: Path,
+    sysconfig_path: Path,
+    platform_config_path: Path,
+) -> None:
+    """Convert a virtual environment into a cross-platform environment.
+
+    :param venv_path: The path to the root of the venv.
+    :param sysconfig_path: The path containing sysconfigdata files for the
+        target platform.
+    :param platform_config_path: The path containing the cross-venv support
+        scripts (_cross_venv.py and the multiarch-specific _cross_*.py).
+    """
+    if not venv_path.exists():
+        msg = f"Virtual environment {venv_path} does not exist."
+        raise ValueError(msg)
+    if not (venv_path / "bin/python3").exists():
+        msg = f"{venv_path} does not appear to be a virtual environment."
+        raise ValueError(msg)
+
+    LIB_PATH = f"lib/python{sys.version_info[0]}.{sys.version_info[1]}"
+
+    # Derive the multiarch tag from the sysconfigdata filename if available;
+    # otherwise fall back to the directory name (BeeWare convention).
+    sysconfigdata_files = list(sysconfig_path.glob("_sysconfigdata_*.py"))
+    if sysconfigdata_files:
+        multiarch_tag = sysconfigdata_files[0].stem.split("_ios_")[1]
+        cross_multiarch = f"_cross_{multiarch_tag.replace('-', '_')}"
+    else:
+        multiarch_tag = sysconfig_path.name
+        cross_multiarch = f"_cross_{multiarch_tag.replace('-', '_')}"
+
+    print(
+        f"Converting {venv_path} into a {multiarch_tag} environment... ",
+        end="",
+    )
+
+    # Update path references in the sysconfigdata to reflect local conditions.
+    venv_site_packages = venv_path / LIB_PATH / "site-packages"
+    localize_sysconfigdata(sysconfig_path, venv_site_packages)
+    localize_sysconfig_vars(sysconfig_path, venv_site_packages)
+    # The multiarch-specific script may be directly in platform_config_path (BeeWare
+    # convention, where all files are co-located) or in a named subdirectory
+    # (cibuildwheel resource layout, where each multiarch has its own subdir).
+    multiarch_script = platform_config_path / f"{cross_multiarch}.py"
+    if not multiarch_script.exists():
+        multiarch_script = platform_config_path / multiarch_tag / f"{cross_multiarch}.py"
+    shutil.copy(
+        multiarch_script,
+        venv_site_packages / f"{cross_multiarch}.py",
+    )
+    shutil.copy(
+        platform_config_path / "_cross_venv.py",
+        venv_site_packages / "_cross_venv.py",
+    )
+    # Write the .pth file that will enable the cross-env modifications
+    (venv_site_packages / "_cross_venv.pth").write_text(
+        f"import {cross_multiarch}; import _cross_venv\n"
+    )
+
+    print("done.")
+
+
+if __name__ == "__main__":
+    try:
+        sysconfig_path = Path(sys.argv[2]).resolve()
+    except IndexError:
+        sysconfig_path = Path(__file__).parent
+
+    try:
+        platform_config_path = Path(sys.argv[3]).resolve()
+    except IndexError:
+        platform_config_path = sysconfig_path
+
+    try:
+        venv_path = Path(sys.argv[1]).resolve()
+        make_cross_venv(venv_path, sysconfig_path, platform_config_path)
+    except IndexError:
+        print("""
+Convert a virtual environment into a cross-platform environment.
+
+Usage:
+    make_cross_venv <venv> (<sysconfig path>) (<platform config path>)
+
+The sysconfig path is the path that contains the `_sysconfigdata-*.py` file
+for the platform being targeted. If an explicit sysconfig path isn't
+provided, it is assumed the directory containing the make_cross_venv script
+also contains the sysconfig data for the interpreter.
+
+The platform config path is the path that contains the cross-venv support
+scripts. If an explicit platform config path isn't provided, it is assumed
+that the sysconfig path also contains the platform configuration files.
+""")

cibuildwheel/resources/ios-support/x86_64-iphonesimulator/_cross_x86_64_iphonesimulator.py

@@ -0,0 +1,79 @@
+# A site package that turns a macOS virtual environment
+# into an x86_64 iphonesimulator cross-platform virtual environment
+import platform
+import subprocess
+import sys
+import sysconfig
+
+###########################################################################
+# sys module patches
+###########################################################################
+sys.cross_compiling = True
+sys.platform = "ios"
+sys.implementation._multiarch = "x86_64-iphonesimulator"
+sys.base_prefix = sysconfig._get_sysconfigdata()["prefix"]
+sys.base_exec_prefix = sysconfig._get_sysconfigdata()["prefix"]
+
+###########################################################################
+# subprocess module patches
+###########################################################################
+subprocess._can_fork_exec = True
+
+
+###########################################################################
+# platform module patches
+###########################################################################
+
+
+def cross_system():
+    return "iOS"
+
+
+def cross_uname():
+    return platform.uname_result(
+        system="iOS",
+        node="build",
+        release="13.0",
+        version="",
+        machine="x86_64",
+    )
+
+
+def cross_ios_ver(system="", release="", model="", is_simulator=False):
+    if system == "":
+        system = "iOS"
+    if release == "":
+        release = "13.0"
+    if model == "":
+        model = "iphonesimulator"
+
+    return platform.IOSVersionInfo(system, release, model, True)
+
+
+platform.system = cross_system
+platform.uname = cross_uname
+platform.ios_ver = cross_ios_ver
+
+
+###########################################################################
+# sysconfig module patches
+###########################################################################
+
+
+def cross_get_platform():
+    return "ios-13.0-x86_64-iphonesimulator"
+
+
+def cross_get_sysconfigdata_name():
+    return "_sysconfigdata__ios_x86_64-iphonesimulator"
+
+
+sysconfig.get_platform = cross_get_platform
+sysconfig._get_sysconfigdata_name = cross_get_sysconfigdata_name
+
+# Ensure module-level values cached at time of import are updated.
+sysconfig._BASE_PREFIX = sys.base_prefix
+sysconfig._BASE_EXEC_PREFIX = sys.base_exec_prefix
+
+# Force sysconfig data to be loaded (and cached).
+sysconfig._init_config_vars()

cibuildwheel/resources/ios-support/x86_64-iphonesimulator/sitecustomize.py

@@ -0,0 +1,22 @@
+# A site customization that can be used to trick pip into installing packages
+# cross-platform. If the folder containing this file is on your PYTHONPATH when
+# you invoke python, the interpreter will behave as if it were running on
+# x86_64 iphonesimulator.
+import sys
+import os
+
+# Apply the cross-platform patch
+import _cross_x86_64_iphonesimulator
+import _cross_venv
+
+
+# Call the next sitecustomize script if there is one
+# (https://nedbatchelder.com/blog/201001/running_code_at_python_startup.html).
+del sys.modules["sitecustomize"]
+this_dir = os.path.dirname(__file__)
+path_index = sys.path.index(this_dir)
+del sys.path[path_index]
+try:
+    import sitecustomize  # noqa: F401
+finally:
+    sys.path.insert(path_index, this_dir)

cibuildwheel/util/resources.py

@@ -18,6 +18,7 @@ VIRTUALENV: Final[Path] = PATH / "virtualenv.toml"
 CIBUILDWHEEL_SCHEMA: Final[Path] = PATH / "cibuildwheel.schema.json"
 PYTHON_BUILD_STANDALONE_RELEASES: Final[Path] = PATH / "python-build-standalone-releases.json"
 TEST_FAIL_CWD_FILE: Final[Path] = PATH / "testing_temp_dir_file.py"
+IOS_SUPPORT_FILES: Final[Path] = PATH / "ios-support"
 
 
 # this value is cached because it's used a lot in unit tests

pyproject.toml

@@ -243,7 +243,10 @@ flake8-annotations.mypy-init-return = true
 ignore = ["PC170", "PP303"]
 
 [tool.check-wheel-contents]
-ignore = ["W002"]  # constraints-*.txt are allowed to be duplicates of one another
+ignore = [
+  "W002",  # constraints-*.txt are allowed to be duplicates of one another
+  "W004",  # "-" is fine for our iOS support files for now
+]
 
 [tool.codespell]
 ignore-words-list = [

test/utils.py

@@ -270,18 +270,15 @@ def _expected_wheels(
         python_abi_tags = ["cp313-cp313"]
         if EnableGroup.PyodidePrerelease in enable_groups:
             python_abi_tags.append("cp314-cp314")
-    elif platform == "android" and python_abi_tags is None:
+    elif (platform == "android" and python_abi_tags is None) or (
+        platform == "ios" and python_abi_tags is None
+    ):
         python_abi_tags = [
             "cp313-cp313",
             "cp314-cp314",
         ]
         if EnableGroup.CPythonPrerelease in enable_groups:
             python_abi_tags += ["cp315-cp315"]
-    elif platform == "ios" and python_abi_tags is None:
-        python_abi_tags = [
-            "cp313-cp313",
-            "cp314-cp314",
-        ]
     elif python_abi_tags is None:
         python_abi_tags = [
             "cp39-cp39",