Add option to dump PEP 517 metadata#940
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So that it can be used with pyproject-hooks.
* Sectionised help text. * Redirected logging messages to stderr by default to prevent piping conflicts. * Factored out the config settings mangler 'cause McCabe was displeased.
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That's a lot more code changes than I hoped and I don't think I can have a worthwhile opinion on them, but |
gaborbernat
approved these changes
Oct 24, 2025
henryiii
reviewed
Oct 24, 2025
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Pull Request Overview
This PR adds support for dumping PEP 517 metadata in JSON format via a new --metadata flag, while also refactoring the internal build and logging infrastructure to improve code organization.
Key changes:
- Introduces
--metadataoption to output wheel metadata as JSON - Refactors build environment bootstrapping into a shared context manager
- Redirects all logging output to stderr to keep stdout clean for metadata output
Reviewed Changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| tests/test_main.py | Adds test coverage for metadata output functionality and updates existing tests to match new logging behavior (stderr instead of stdout) |
| tests/constraints.txt | Updates packaging dependency to version 24.0 |
| src/build/_ctx.py | Refactors subprocess execution to support custom runners and consolidates stdout/stderr streams |
| src/build/main.py | Implements metadata extraction, refactors build environment setup, reorganizes CLI argument groups, and redirects logging to stderr |
| pyproject.toml | Updates packaging and mypy dependency versions |
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Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Signed-off-by: Henry Schreiner <henryfs@princeton.edu>
Contributor
|
I'm curious, how are you supposed to use this since it prints out to stdout, where we are already printing things (and the backend might, too)? $ uv run pyproject-build --metadata
* Creating isolated environment: virtualenv+pip...
* Installing packages in isolated environment:
- flit-core >= 3.11
* Getting build dependencies for wheel...
* Getting metadata for wheel...
{
"license_files": [
"LICENSE"
],
"provides_extra": [
"uv",
"virtualenv"
],
"author_email": "Filipe Laíns <lains@riseup.net>, Bernát Gábor <gaborjbernat@gmail.com>, layday <layday@protonmail.com>, Henry Schreiner <henryschreineriii@gmail.com>",
"metadata_version": "2.4",
"classifiers": [
"Programming Language :: Python :: 3",
"Programming Language :: Python :: 3 :: Only",
"Programming Language :: Python :: 3.9",
"Programming Language :: Python :: 3.10",
"Programming Language :: Python :: 3.11",
"Programming Language :: Python :: 3.12",
"Programming Language :: Python :: 3.13",
"Programming Language :: Python :: 3.14",
"Programming Language :: Python :: Implementation :: CPython",
"Programming Language :: Python :: Implementation :: PyPy"
],
"license_expression": "MIT",
"requires_python": ">= 3.9",
"version": "1.3.0",
* Creating isolated environment: virtualenv+pip...
* Installing packages in isolated environment:
- flit-core >= 3.11
* Getting build dependencies for wheel...
* Getting metadata for wheel...
{
"name": "build",
"description_content_type": "text/markdown",
"license_files": [
"LICENSE"
],
"provides_extra": [
"uv",
"virtualenv"
],
"project_urls": {
"changelog": "https://build.pypa.io/en/stable/changelog.html",
"homepage": "https://build.pypa.io",
"issues": "https://github.com/pypa/build/issues",
"source": "https://github.com/pypa/build"
},
"author_email": "Filipe Laíns <lains@riseup.net>, Bernát Gábor <gaborjbernat@gmail.com>, layday <layday@protonmail.com>, Henry Schreiner <henryschreineriii@gmail.com>",
"classifiers": [
"Programming Language :: Python :: 3",
"Programming Language :: Python :: 3 :: Only",
"Programming Language :: Python :: 3.9",
"Programming Language :: Python :: 3.10",
"Programming Language :: Python :: 3.11",
"Programming Language :: Python :: 3.12",
"project_urls": {
"changelog": "https://build.pypa.io/en/stable/changelog.html",
"homepage": "https://build.pypa.io",
"issues": "https://github.com/pypa/build/issues",
"source": "https://github.com/pypa/build"
},
"name": "build",
"description_content_type": "text/markdown",
"requires_dist": [
"packaging >= 24.0",
"pyproject_hooks",
"colorama; os_name == \"nt\"",
"importlib-metadata >= 4.6; python_full_version < \"3.10.2\"",
"tomli >= 1.1.0; python_version < \"3.11\"",
"uv >= 0.1.18 ; extra == \"uv\"",
"virtualenv >= 20.11 ; extra == \"virtualenv\" and ( python_version < '3.10')",
"virtualenv >= 20.17 ; extra == \"virtualenv\" and ( python_version >= '3.10' and python_version < '3.14')",
"virtualenv >= 20.31 ; extra == \"virtualenv\" and ( python_version >= '3.14')"
],
"summary": "A simple, correct Python build frontend",
"description": "# build\n\n[](https://results.pre-commit.ci/latest/github/pypa/build/main)\n[](https://github.com/pypa/build/actions/workflows/test.yml)\n[](https://codecov.io/gh/pypa/build)\n\n[](https://build.pypa.io/en/latest/?badge=latest)\n[](https://pypi.org/project/build/)\n[](https://discord.gg/pypa)\n\nA simple, correct Python build frontend.\n\nSee the [documentation](https://build.pypa.io) for more information.\n\n### Installation\n\n`build` can be installed via `pip` or an equivalent via:\n\n```console\n$ pip install build\n```\n\n### Usage\n\n```console\n$ python -m build\n```\n\nThis will build the package in an isolated environment, generating a\nsource-distribution and wheel in the directory `dist/`. See the\n[documentation](https://build.pypa.io) for full information. Build is also\navailable via the command line as `pyproject-build` once installed.\n\n### Common arguments\n\n- `--sdist` (`-s`): Produce just an SDist\n- `--wheel` (`-w`): Produce just a wheel\n- `--metadata`: Produce just the metadata as JSON. Cannot be used with `--sdist`/`--wheel`.\n- `-C<option>=<value>`: A Config-setting, the PEP 517 way of passing options to a backend. Can be passed multiple times. Matching options will make a list. Note that setuptools has very limited support.\n- `--config-json=<value>`: An alternative way to pass in complex config settings as JSON strings. Can't be used with `-C`.\n- `--installer`: Pick an installer for the isolated build (`pip` or `uv`).\n- `--no-isolation` (`-n`): Disable build isolation.\n- `--skip-dependency-check` (`-x`): Disable dependency checking when not isolated; this should be done if some requirements or version ranges are not required for non-isolated builds.\n- `--outdir` (`-o`): The output directory (defaults to `dist`)\n\nSome common combinations of arguments:\n\n- `--sdist --wheel` (`-sw`): Produce and SDist and a wheel, both from the source distribution. The default (if no flag is passed) is to build an SDist and then build a wheel _from_ the SDist.\n- `-nx`: Disable build isolation and dependency checking. Identical to pip and uv's `--no-build-isolation` flag.\n\n### Integration with other tools\n\n#### pipx\n\nIf you use [pipx][], such as in GitHub Actions, the following command will download\nand run build in one step:\n\n```console\n$ pipx run build\n```\n\n#### uv\n\nIf you want to use [uv][] to speed up the virtual environment creation, you can\nuse `--installer=uv`. You can get a Python wheel for `uv` with the `[uv]`\nextra. For example, using pipx like above:\n\n```console\n$ pipx run 'build[uv]' --installer uv\n```\n\nIf you already have uv, you don't need the extra. For example:\n\n```console\n$ uvx --from build pyproject-build --installer uv\n```\n\n#### cibuildwheel\n\nIf you are using [cibuildwheel][], build is integrated and the default builder in 3.0+. If you want to use `uv` as the installer, you can use:\n\n```toml\n[tool.cibuildwheel]\nbuild-frontend = \"build[uv]\"\n```\n\n(Be sure to pre-install uv before running cibuildwheel for this one!)\n\n#### Conda-forge\n\nOn conda-forge, this package is called [python-build][].\n\n### Code of Conduct\n\nEveryone interacting in the build's codebase, issue trackers, chat rooms, and mailing lists is expected to follow\nthe [PSF Code of Conduct].\n\n[psf code of conduct]: https://github.com/pypa/.github/blob/main/CODE_OF_CONDUCT.md\n[pipx]: https://pipx.pypa.io\n[uv]: https://docs.astral.sh/uv/\n[cibuildwheel]: https://cibuildwheel.pypa.io\n[python-build]: https://github.com/conda-forge/python-build-feedstock\n\n"
}I'm thinking we could provide a new |
Contributor
|
Ahh, I see the |
Member
Author
|
You don't need to redirect stderr to |
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