feat: if for free-threading (#819)

~~I think this won't work on Windows yet, we'll need to find the flags
another way there, I think.~~ Now uses packaging.tags. Close #770.

---------

Signed-off-by: Henry Schreiner <[email protected]>

Author: henryiii

README.md

@@ -63,8 +63,8 @@ features over classic Scikit-build:
   soon)
 - Experimental editable mode support, with optional experimental auto rebuilds
   on import and optional in-place mode
-- Supports WebAssembly (Emscripten/Pyodide).
-- Supports free-threaded Python 3.13.
+- Supports WebAssembly (Emscripten/[Pyodide](https://pyodide.org)).
+- Supports [free-threaded Python 3.13](https://py-free-threading.github.io).
 
 The following limitations are present compared to classic scikit-build:
 
@@ -117,7 +117,7 @@ the minimum to get started.
 An example `CMakeLists.txt`:
 
 ```cmake
-cmake_minimum_required(VERSION 3.15...3.27)
+cmake_minimum_required(VERSION 3.15...3.30)
 project(${SKBUILD_PROJECT_NAME} LANGUAGES C)
 
 find_package(Python COMPONENTS Interpreter Development.Module REQUIRED)

docs/overrides.md

@@ -29,7 +29,7 @@ Example:
 
 ```toml
 [[tool.scikit-build.overrides]]
-if.python_version = ">=3.13"
+if.python-version = ">=3.13"
 wheel.cmake = false
 ```
 
@@ -84,6 +84,10 @@ A few sample values:
 | Windows | ARM           | `ARM64`           |
 
 
+### `abi-flags` (string)
+
+A sorted list of the ABI flags. `t` is the free-threaded build.
+
 ### `platform-node` (string)
 
 The value of `platform.node()`. This is generally your computer's name. Takes a

src/scikit_build_core/builder/sysconfig.py

@@ -7,12 +7,15 @@
 from pathlib import Path
 from typing import TYPE_CHECKING
 
+import packaging.tags
+
 from .._logging import logger, rich_print
 
 if TYPE_CHECKING:
     from collections.abc import Mapping
 
 __all__ = [
+    "get_abi_flags",
     "get_cmake_platform",
     "get_numpy_include_dir",
     "get_python_include_dir",
@@ -184,6 +187,19 @@ def get_numpy_include_dir() -> Path | None:
     return Path(np.get_include())
 
 
+def get_abi_flags() -> str:
+    """
+    Return the ABI flags for the current Python interpreter. Derived from
+    ``packaging.tags.sys_tags()`` since that works on Windows.
+    """
+
+    most_compatible = next(iter(packaging.tags.sys_tags()))
+    full_abi = most_compatible.abi
+    vers = packaging.tags.interpreter_version()
+    abi_flags = full_abi[full_abi.find(vers) + len(vers) :]
+    return "".join(sorted(abi_flags))
+
+
 def info_print(*, color: str = "") -> None:
     """
     Print information about the Python environment.
@@ -208,6 +224,7 @@ def info_print(*, color: str = "") -> None:
     rich_print(
         f"[bold {color}]Detected ABI3 SOABI:[/bold] {get_soabi(os.environ, abi3=True)}"
     )
+    rich_print(f"[bold {color}Detected ABI flags:[/bold] {get_abi_flags()}")
 
 
 if __name__ == "__main__":

src/scikit_build_core/resources/scikit-build.schema.json

@@ -667,6 +667,10 @@
           "type": "boolean",
           "description": "Whether a cmake wheel is known to be provided for this system."
         },
+        "abi-flags": {
+          "type": "string",
+          "description": "A sorted string of the abi flags. Takes a regex."
+        },
         "env": {
           "type": "object",
           "patternProperties": {

src/scikit_build_core/settings/skbuild_overrides.py

@@ -12,6 +12,7 @@
 
 from .._compat import tomllib
 from .._logging import logger
+from ..builder.sysconfig import get_abi_flags
 from ..cmake import CMake
 from ..errors import CMakeNotFoundError
 from ..resources import resources
@@ -76,6 +77,7 @@ def override_match(
     failed: bool | None = None,
     system_cmake: str | None = None,
     cmake_wheel: bool | None = None,
+    abi_flags: str | None = None,
 ) -> tuple[dict[str, str], set[str]]:
     """
     Check if the current environment matches the overrides. Returns a dict
@@ -191,6 +193,14 @@ def override_match(
         else:
             failed_set.add("cmake-wheel")
 
+    if abi_flags is not None:
+        current_abi_flags = get_abi_flags()
+        match_msg = regex_match(current_abi_flags, abi_flags)
+        if match_msg:
+            passed_dict["abi-flags"] = match_msg
+        else:
+            failed_set.add("abi-flags")
+
     if env:
         for key, value in env.items():
             if key not in current_env:

src/scikit_build_core/settings/skbuild_schema.py

@@ -132,6 +132,10 @@ def generate_skbuild_schema(tool_name: str = "scikit-build") -> dict[str, Any]:
                 "type": "boolean",
                 "description": "Whether a cmake wheel is known to be provided for this system.",
             },
+            "abi-flags": {
+                "type": "string",
+                "description": "A sorted string of the abi flags. Takes a regex.",
+            },
             "env": {
                 "type": "object",
                 "patternProperties": {

tests/test_settings_overrides.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import sysconfig
 import typing
 from pathlib import Path
 from textwrap import dedent
@@ -540,6 +541,7 @@ def test_skbuild_overrides_from_sdist(
         tmp_path / ("from_sdist" if from_sdist else "not_from_sdist") / "pyproject.toml"
     )
     pyproject_toml.parent.mkdir(exist_ok=True)
+
     pyproject_toml.write_text(
         dedent(
             """\
@@ -666,3 +668,23 @@ def test_system_cmake(
     settings_reader = SettingsReader.from_file(pyproject_toml, retry=False)
     settings = settings_reader.settings
     assert settings.wheel.cmake == (cmake_version == "3.27")
+
+
+def test_free_threaded_override(tmp_path: Path):
+    pyproject_toml = tmp_path / "pyproject.toml"
+    pyproject_toml.write_text(
+        dedent(
+            """\
+            [tool.scikit-build]
+            wheel.cmake = false
+
+            [[tool.scikit-build.overrides]]
+            if.abi-flags = "t"
+            wheel.cmake = true
+            """
+        )
+    )
+
+    settings_reader = SettingsReader.from_file(pyproject_toml, state="wheel")
+    settings = settings_reader.settings
+    assert settings.wheel.cmake == bool(sysconfig.get_config_var("Py_GIL_DISABLED"))