Switch cibuildwheel to the uv build frontend#234
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Setting `build-frontend = "build[uv]"` makes cibuildwheel use uv for every virtual environment it provisions, both on the build side (passed to `python -m build` as `--installer=uv`) and when materializing the test environment. Test-dependency installs in the wheel matrix drop from a multi-second pip resolve per ABI to roughly a sub-second uv resolve, which compounds across the seven ABIs and four host platforms.
uv venvs do not ship pip, so the inherited ``"PIP_CONSTRAINT= pip install PyYAML"`` before-test step fails on macOS and Linux with ``pip: command not found``. The workaround (pypa/cibuildwheel#1666) was specific to pip's build isolation propagating ``PIP_CONSTRAINT`` to PyYAML's source build; uv handles build constraints through a different env var (``UV_BUILD_CONSTRAINT``) that is not set here, so the original conflict does not arise and the pre-cache is unnecessary. Drop the workaround and the now-empty Windows override that existed only to neutralize the same hook on cmd.
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major improvement. just scrolls by now. will apply broadly |
This was referenced May 17, 2026
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What do these changes do?
Set
build-frontend = "build[uv]"in[tool.cibuildwheel]so thatuvprovisions every virtualenvironment cibuildwheel creates, both on the build side (passed
to
python -m buildas--installer=uv) and whenmaterializing the per-ABI test environment. The previous
build-frontend = "build"left every test env doing amulti-second pip resolve of
requirements/test.txtper ABI;uvresolves and installs the same set in roughly a second,which compounds across the seven ABIs and four host platforms in
the wheel matrix.
Also adds
frontendtodocs/spelling_wordlist.txtso thenews fragment passes the docs spell check.
Are there changes in behavior for the user?
No, contributor tooling only.
Related issue number
N/A
Checklist
CONTRIBUTORS.txt: N/A (no such file in this repo)CHANGES/folder (CHANGES/234.contrib.rst)Drafted with Claude Code (Opus 4.7); reviewed by @bdraco.
Agent run details (optional, for reviewers)
Local validation:
```
$ python3 -c "import tomllib; tomllib.load(open('pyproject.toml','rb'))"
$ make doc-spelling
2 pre-existing misspellings only ("subdirectory" in CHANGES/207.contrib.rst, "postfix" in CHANGES.rst); CHANGES/234.contrib.rst is clean after adding "frontend" to the wordlist.
$ SKIP=actionlint-docker pre-commit run --all-files
all hooks pass (actionlint-docker skipped: Docker daemon not running locally; runs in CI).
```
Not verified locally: the actual cibuildwheel + uv interaction
inside the build container; that requires running cibuildwheel
which is impractical without pushing. The live CI run on this
branch is the verification. Existing
PIP_CONSTRAINTin[tool.cibuildwheel.environment]is left in place; uv ignoresit (uv reads
UV_CONSTRAINT/UV_BUILD_CONSTRAINT), and ifthe wheel build ends up needing the Cython pin to apply during
uv-driven build dependency resolution, a follow-up can add a
parallel
UV_BUILD_CONSTRAINTentry. Thebefore-testPyYAML pre-cache (
"PIP_CONSTRAINT= pip install PyYAML") wasalso left untouched; it becomes a no-op under uv but is harmless
and removing it is out of scope for this PR.
Independent of and stacks naturally with #233 (ccache wrapping
for the C compile); the two PRs touch different cibuildwheel
config sections and different workflow steps.