Add `METADATA.json` and `WHEEL.json` in uv build backend by konstin · Pull Request #15510 · astral-sh/uv

konstin · 2025-08-25T08:35:45Z

https://discuss.python.org/t/pep-819-json-package-metadata/105558

Add an experimental JSON format for METADATA and WHEEL files in the uv build backend to have a reference what it would look like and to demonstrate that the actual change is just a few lines, how much easier it is than the existing email header format.

The change is overwhelmingly adding the preview feature as it's the first preview item in the build backend, writing the actual JSON is only a couple of lines.

crates/uv-build-backend/src/lib.rs

konstin · 2025-08-26T15:32:45Z

Before merging, we need to extend this to include the full transformations from https://peps.python.org/pep-0566/#json-compatible-metadata

konstin · 2026-01-06T12:09:21Z

PEP 819 is up, so I'd like to merge this as a preview feature.

EliteTK

Fun fact:

This PR adds 88 (118) new instances of the word "preview" to uv. For a grand total of 1525 (1935) instances. (Counts in brackets are when just searching for "preview" rather than for words.)

crates/uv-build/src/main.rs

crates/uv-build-backend/src/lib.rs

crates/uv-pypi-types/src/metadata/metadata23.rs

EliteTK · 2026-01-09T13:47:12Z

crates/uv-pypi-types/src/metadata/metadata23.rs

+    /// Read the `METADATA` format.
+    pub fn from_iter_str(project_urls: impl IntoIterator<Item = String>) -> Self {
+        Self(
+            project_urls
+                .into_iter()
+                .map(|project_url| {
+                    let (label, url) = project_url.split_once(',').unwrap_or((&project_url, ""));
+                    // TODO(konsti): The spec says separated by comma, but it's actually comma and a
+                    // space.
+                    (label.trim().to_string(), url.trim().to_string())
+                })
+                .collect(),
+        )
+    }
+
+    /// Write the `METADATA` format.
+    pub fn to_vec_str(&self) -> Vec<String> {
+        self.0
+            .iter()
+            .map(|(label, url)| format!("{label}, {url}"))
+            .collect()
+    }


nit: I think this parsing and serialisation belongs in a ProjectUrl type. But I can see how that would be a bit of churn due to the overarching need for IndexMap.

Add an experimental JSON format for METADATA and WHEEL files in the uv build backend to have a reference what it would look like and to demonstrate that the actual change is just a few lines, how much easier it is than the existing email-ish format.

This MR contains the following updates: | Package | Update | Change | |---|---|---| | [astral-sh/uv](https://github.com/astral-sh/uv) | patch | `0.9.24` → `0.9.26` | MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot). **Proposed changes to behavior should be submitted there as MRs.** --- ### Release Notes <details> <summary>astral-sh/uv (astral-sh/uv)</summary> ### [`v0.9.26`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0926) [Compare Source](astral-sh/uv@0.9.25...0.9.26) Released on 2026-01-15. ##### Python - Add CPython 3.15.0a5 ##### Enhancements - Add a hint to update uv when a managed Python download is not found ([#17461](astral-sh/uv#17461)) - Improve cache initialization failure error message ([#17469](astral-sh/uv#17469)) - Improve error message for abi3 wheels on free-threaded Python ([#17442](astral-sh/uv#17442)) - Add support for `--no-sources-package` ([#14910](astral-sh/uv#14910)) ##### Preview features - Add `METADATA.json` and `WHEEL.json` in uv build backend ([#15510](astral-sh/uv#15510)) - Add support for GCS request signing ([#17474](astral-sh/uv#17474)) - Adjust the process ulimit to the maximum allowed on startup ([#17464](astral-sh/uv#17464)) ##### Bug fixes - Lock to avoid concurrent refresh of pyx tokens ([#17479](astral-sh/uv#17479)) ##### Documentation - Add linting and formatting instructions to the CONTRIBUTING guide ([#17470](astral-sh/uv#17470)) - Avoid rendering `pyproject.toml` examples for more system-level settings ([#17462](astral-sh/uv#17462)) ### [`v0.9.25`](https://github.com/astral-sh/uv/blob/HEAD/CHANGELOG.md#0925) [Compare Source](astral-sh/uv@0.9.24...0.9.25) Released on 2026-01-13. ##### Python - Add CPython 3.15.0a4 - Upgrade Tcl/Tk used by CPython to 9.0 ##### Enhancements - Add `--compile-bytecode` to `uv python install` and `uv python upgrade` to compile the standard library ([#17088](astral-sh/uv#17088)) - Allow disabling `exclude-newer` per package ([#16854](astral-sh/uv#16854)) - Broadcast `WM_SETTINGCHANGE` on `uv tool update-shell` ([#17404](astral-sh/uv#17404)) ##### Preview features - Detect workspace from `uv run` target ([#17423](astral-sh/uv#17423)) ##### Bug fixes - Avoid unwrapping size for file responses ([#17434](astral-sh/uv#17434)) - Use keyring authentication when retrieving `tool@latest` version ([#17448](astral-sh/uv#17448)) - Use latest Pyodide version for each python version ([#17372](astral-sh/uv#17372)) - Improve trampoline file handle closing ([#17374](astral-sh/uv#17374)) - Fix error message when installing musl python on armv7 ([#17213](astral-sh/uv#17213)) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this MR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this MR, check this box --- This MR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

konstin added preview Experimental behavior build-backend labels Aug 25, 2025

konstin commented Aug 25, 2025

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konstin changed the title ~~Add METADATA.json and WHEEL.json to build backend~~ Add METADATA.json and WHEEL.json in uv build backend Aug 25, 2025

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EliteTK approved these changes Jan 9, 2026

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charliermarsh and others added 3 commits January 14, 2026 17:45

A metadata and wheel snapshots

c64fcaa

Rebase fixup

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Test fixtures

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konstin merged commit 0ab603e into main Jan 14, 2026
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konstin deleted the konsti/json-metadata branch January 14, 2026 18:52

BrewTestBot mentioned this pull request Jan 15, 2026

uv 0.9.26 Homebrew/homebrew-core#263018

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Add `METADATA.json` and `WHEEL.json` in uv build backend#15510

Add `METADATA.json` and `WHEEL.json` in uv build backend#15510
konstin merged 4 commits intomainfrom
konsti/json-metadata

konstin commented Aug 25, 2025 •

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konstin commented Aug 25, 2025 •

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