feat: drop Python 3.8

[henryiii]

Getting ready to drop 3.8.

🤖 Assisted-by: Copilot:Kimi-K2.6

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the project to require Python 3.9+ by removing Python 3.8 compatibility code paths, adjusting ABI3 defaults, and updating docs/CI to match the new minimum supported version.

Changes:

• Bumps requires-python / python_requires constraints across project and test packages to >=3.9.
• Removes Python 3.8-specific compatibility branches (typing backports, distutils.sysconfig, importlib_resources) and modernizes type annotations to built-in generics.
• Updates CI matrix, docs, and ABI3 examples/tests to target cp39/SABI 3.9.

Reviewed changes

Copilot reviewed 57 out of 57 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/test_setuptools_pep517.py	Updates expected metadata to Requires-Python: >=3.9.
tests/test_setuptools_abi3.py	Updates expected ABI3 wheel tag from cp38 to cp39.
tests/test_settings.py	Modernizes typing annotations to built-in generics for 3.9+.
tests/test_pyproject_pep660.py	Removes pre-3.8.7 branching and simplifies Windows extension fallback.
tests/test_pyproject_pep518.py	Updates expected metadata to Requires-Python: >=3.9.
tests/test_pyproject_pep517.py	Updates expected metadata to Requires-Python: >=3.9.
tests/test_pyproject_abi3.py	Updates expected ABI3 wheel tag assertions to cp39.
tests/test_module_dir.py	Changes Generator import strategy for typing.
tests/test_json_schema.py	Switches typing inputs in schema conversion tests to built-in generics.
tests/test_editable_unit.py	Removes version gating for resource-file imports in editable tests.
tests/test_editable.py	Removes Python <3.9 skip for importlib.resources.files.
tests/packages/toml_setuptools_ext/pyproject.toml	Bumps requires-python to >=3.9.
tests/packages/simple_setuptools_ext/setup.py	Bumps python_requires to >=3.9.
tests/packages/simple_pyproject_source_dir/pyproject.toml	Bumps requires-python to >=3.9.
tests/packages/simple_pyproject_script_with_flags/pyproject.toml	Bumps requires-python to >=3.9.
tests/packages/simple_pyproject_ext/pyproject.toml	Bumps requires-python to >=3.9.
tests/packages/navigate_editable/python/shared_pkg/py_module.py	Drops importlib_resources fallback and uses stdlib importlib.resources.
tests/packages/navigate_editable/pyproject.toml	Removes conditional importlib-resources dependency for <3.9.
tests/packages/mixed_setuptools/setup.cfg	Bumps python_requires to >=3.9.
tests/packages/fortran_example/pyproject.toml	Bumps requires-python to >=3.9.
tests/packages/filepath_pure/pyproject.toml	Bumps requires-python to >=3.9.
tests/packages/abi3_setuptools_ext/setup.cfg	Bumps python_requires and updates limited API to cp39.
tests/packages/abi3_setuptools_ext/CMakeLists.txt	Updates USE_SABI from 3.8 to 3.9.
tests/packages/abi3_pyproject_ext/pyproject.toml	Updates ABI3 config tag from cp38 to cp39.
tests/packages/abi3_pyproject_ext/CMakeLists.txt	Updates SABI version check and failure message for 3.9.
tests/conftest.py	Simplifies sdist hash selection by removing 3.8/3.9 branching.
src/scikit_build_core/settings/skbuild_model.py	Replaces typing.List/Dict with built-in generics; updates cp38 references.
src/scikit_build_core/file_api/reply.py	Updates typing to built-in generics and type[T] annotations.
src/scikit_build_core/file_api/model/toolchains.py	Switches model field types to built-in generics.
src/scikit_build_core/file_api/model/index.py	Switches model field types to built-in generics.
src/scikit_build_core/file_api/model/directory.py	Switches model field types to built-in generics.
src/scikit_build_core/file_api/model/common.py	Updates __dir__ return type to built-in generic.
src/scikit_build_core/file_api/model/codemodel.py	Switches model field types to built-in generics.
src/scikit_build_core/file_api/model/cmakefiles.py	Switches model field types to built-in generics.
src/scikit_build_core/file_api/model/cache.py	Switches model field types to built-in generics.
src/scikit_build_core/file_api/_cattrs_converter.py	Updates typing to built-in generics and type[T] annotations.
src/scikit_build_core/cmake.py	Refactors context manager usage and updates comment re: missing_ok.
src/scikit_build_core/builder/sysconfig.py	Uses Python 3.9+ APIs (removeprefix, sysconfig only).
src/scikit_build_core/build/_file_processor.py	Removes 3.9 workaround and uses Path.is_relative_to directly.
src/scikit_build_core/_logging.py	Uses functools.cache (3.9+) in place of lru_cache(maxsize=None).
src/scikit_build_core/_compat/typing.py	Drops pre-3.9 conditional imports for Annotated/get_args/get_origin.
src/scikit_build_core/_compat/importlib/resources.py	Drops importlib_resources fallback for <3.9.
src/scikit_build_core/_compat/importlib/metadata.py	Uses built-in generics for EntryPoints alias.
pyproject.toml	Bumps min Python to 3.9, updates deps/extras, and updates pylint py-version.
docs/reference/configs.md	Updates docs to reference cp39 for stable ABI configuration.
docs/guide/cmakelists.md	Updates example wheel.py-api from cp38 to cp39.
docs/examples/getting_started/nanobind/CMakeLists.txt	Updates minimum Python in CMake find_package to 3.9.
docs/examples/getting_started/abi3/pyproject.toml	Updates example wheel.py-api from cp38 to cp39.
docs/examples/getting_started/abi3/CMakeLists.txt	Updates USE_SABI from 3.8 to 3.9.
docs/examples/downstream/pybind11_example/pyproject.toml	Updates example requires-python and classifiers to drop 3.8.
docs/examples/downstream/pybind11_example/README.md	Updates stated minimum Python version to 3.9+.
docs/examples/downstream/nanobind_example/pyproject.toml	Updates example requires-python to >=3.9.
docs/examples/downstream/nanobind_example/CMakeLists.txt	Updates minimum Python in CMake find_package to 3.9.
docs/configuration/index.md	Updates ABI3 example to cp39 and edits known limitations text.
README.md	Updates stated minimum supported Python version to 3.9.
.github/workflows/ci.yml	Removes 3.8 from CI, updates PyPy baseline, and shifts job entries to 3.9+.
.github/CONTRIBUTING.md	Updates contributor examples to require Python 3.9+.

Comments suppressed due to low confidence (1)

tests/test_module_dir.py:1

• Importing Generator only under TYPE_CHECKING will break at runtime if it is referenced in annotations in this module (since annotations are evaluated eagerly without from __future__ import annotations). Either import Generator unconditionally (preferably from collections.abc) or add from __future__ import annotations and keep the TYPE_CHECKING import.

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[Copilot]

This parenthesized multi-context-manager with (...) syntax is only supported starting in Python 3.10. Since this PR sets the minimum supported version to 3.9, this will be a syntax error on Python 3.9. Use a Python 3.9-compatible with statement (single line, backslash continuation, or nested with) instead.

Suggested change

	with (
	contextlib.suppress(FileNotFoundError),
	skbuild_info.open("r", encoding="utf-8") as f,
	):
	info = json.load(f)
	with contextlib.suppress(FileNotFoundError):
	with skbuild_info.open("r", encoding="utf-8") as f:
	info = json.load(f)

[Copilot]

This line assigns list[Source] to a class attribute instead of declaring a dataclass field. If sources is intended to be part of the CMake codemodel Target schema, it should be a proper type annotation (e.g., sources: list[Source] = ... or sources: list[Source]) so dataclasses will treat it as a field.

Suggested change

	sources = list[Source]
	sources: list[Source] = dataclasses.field(default_factory=list)

[Copilot]

input_dict appears to be used as the kwargs dict passed into target(**input_dict), so its values are instances (converted field values), not types. The annotation dict[str, type[Any]] is misleading and will cause type-checker noise; it should be dict[str, Any] (or more specific per-field typing if desired).

Suggested change

	input_dict: dict[str, type[Any]] = {}
	input_dict: InputDict = {}

[Copilot]

Now that Python 3.9 is the minimum supported version, calling out that a feature is 'not properly supported' specifically on 3.9 is high impact but lacks actionable guidance. Consider adding a brief explanation/workaround (or a link to an issue) and clarifying whether this limitation still applies after dropping 3.8.

[LecrisUT]

Let me know when you need the additional pair of eyes on this. I noticed some errors at first glance (not caught by copilot), hence why added myself in the reviewer