Add `METADATA.json` and `WHEEL.json` to build backend

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.

Cargo.lock

@@ -5186,6 +5186,8 @@ version = "0.8.13"
 dependencies = [
  "anyhow",
  "uv-build-backend",
+ "uv-preview",
+ "uv-static",
  "uv-version",
 ]
 
@@ -5205,6 +5207,7 @@ dependencies = [
  "rustc-hash",
  "schemars",
  "serde",
+ "serde_json",
  "sha2",
  "spdx",
  "tar",
@@ -5221,6 +5224,7 @@ dependencies = [
  "uv-pep440",
  "uv-pep508",
  "uv-platform-tags",
+ "uv-preview",
  "uv-pypi-types",
  "uv-version",
  "uv-warnings",
@@ -6346,6 +6350,7 @@ dependencies = [
 name = "uv-static"
 version = "0.0.1"
 dependencies = [
+ "thiserror 2.0.12",
  "uv-macros",
 ]
 

crates/uv-build-backend/Cargo.toml

@@ -22,6 +22,7 @@ uv-options-metadata = { workspace = true }
 uv-pep440 = { workspace = true }
 uv-pep508 = { workspace = true }
 uv-platform-tags = { workspace = true }
+uv-preview = { workspace = true }
 uv-pypi-types = { workspace = true }
 uv-version = { workspace = true }
 uv-warnings = { workspace = true }
@@ -35,6 +36,7 @@ itertools = { workspace = true }
 rustc-hash = { workspace = true }
 schemars = { workspace = true, optional = true }
 serde = { workspace = true }
+serde_json = { workspace = true }
 sha2 = { workspace = true }
 spdx = { workspace = true }
 tar = { workspace = true }

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

@@ -59,6 +59,8 @@ pub enum Error {
     Zip(#[from] zip::result::ZipError),
     #[error("Failed to write RECORD file")]
     Csv(#[from] csv::Error),
+    #[error("Failed to write JSON metadata file")]
+    Json(#[source] serde_json::Error),
     #[error("Expected a Python module at: `{}`", _0.user_display())]
     MissingInitPy(PathBuf),
     #[error("For namespace packages, `__init__.py[i]` is not allowed in parent directory: `{}`", _0.user_display())]
@@ -362,6 +364,7 @@ mod tests {
     use tempfile::TempDir;
     use uv_distribution_filename::{SourceDistFilename, WheelFilename};
     use uv_fs::{copy_dir_all, relative_to};
+    use uv_preview::{Preview, PreviewFeatures};
 
     const MOCK_UV_VERSION: &str = "1.0.0+test";
 
@@ -388,11 +391,11 @@ mod tests {
 
     /// Run both a direct wheel build and an indirect wheel build through a source distribution,
     /// while checking that directly built wheel and indirectly built wheel are the same.
-    fn build(source_root: &Path, dist: &Path) -> Result<BuildResults, Error> {
+    fn build(source_root: &Path, dist: &Path, preview: Preview) -> Result<BuildResults, Error> {
         // Build a direct wheel, capture all its properties to compare it with the indirect wheel
         // latest and remove it since it has the same filename as the indirect wheel.
-        let (_name, direct_wheel_list_files) = list_wheel(source_root, MOCK_UV_VERSION)?;
+        let (_name, direct_wheel_list_files) = list_wheel(source_root, MOCK_UV_VERSION, preview)?;
-        let direct_wheel_filename = build_wheel(source_root, dist, None, MOCK_UV_VERSION)?;
+        let direct_wheel_filename = build_wheel(source_root, dist, None, MOCK_UV_VERSION, preview)?;
         let direct_wheel_path = dist.join(direct_wheel_filename.to_string());
         let direct_wheel_contents = wheel_contents(&direct_wheel_path);
         let direct_wheel_hash = sha2::Sha256::digest(fs_err::read(&direct_wheel_path)?);
@@ -402,7 +405,7 @@ mod tests {
         let (_name, source_dist_list_files) = list_source_dist(source_root, MOCK_UV_VERSION)?;
         // TODO(konsti): This should run in the unpacked source dist tempdir, but we need to
         // normalize the path.
-        let (_name, wheel_list_files) = list_wheel(source_root, MOCK_UV_VERSION)?;
+        let (_name, wheel_list_files) = list_wheel(source_root, MOCK_UV_VERSION, preview)?;
         let source_dist_filename = build_source_dist(source_root, dist, MOCK_UV_VERSION)?;
         let source_dist_path = dist.join(source_dist_filename.to_string());
         let source_dist_contents = sdist_contents(&source_dist_path);
@@ -417,7 +420,13 @@ mod tests {
             source_dist_filename.name.as_dist_info_name(),
             source_dist_filename.version
         ));
-        let wheel_filename = build_wheel(&sdist_top_level_directory, dist, None, MOCK_UV_VERSION)?;
+        let wheel_filename = build_wheel(
+            &sdist_top_level_directory,
+            dist,
+            None,
+            MOCK_UV_VERSION,
+            preview,
+        )?;
         let wheel_contents = wheel_contents(&dist.join(wheel_filename.to_string()));
 
         // Check that direct and indirect wheels are identical.
@@ -441,7 +450,7 @@ mod tests {
 
     fn build_err(source_root: &Path) -> String {
         let dist = TempDir::new().unwrap();
-        let build_err = build(source_root, dist.path()).unwrap_err();
+        let build_err = build(source_root, dist.path(), Preview::default()).unwrap_err();
         let err_message: String = format_err(&build_err)
             .replace(&source_root.user_display().to_string(), "[TEMP_PATH]")
             .replace('\\', "/");
@@ -558,7 +567,7 @@ mod tests {
 
         // Perform both the direct and the indirect build.
         let dist = TempDir::new().unwrap();
-        let build = build(src.path(), dist.path()).unwrap();
+        let build = build(src.path(), dist.path(), Preview::default()).unwrap();
 
         let source_dist_path = dist.path().join(build.source_dist_filename.to_string());
         assert_eq!(
@@ -622,7 +631,7 @@ mod tests {
         // Check that the wheel is reproducible across platforms.
         assert_snapshot!(
             format!("{:x}", sha2::Sha256::digest(fs_err::read(&wheel_path).unwrap())),
-            @"319afb04e87caf894b1362b508ec745253c6d241423ea59021694d2015e821da"
+            @"dbe56fd8bd52184095b2e0ea3e83c95d1bc8b4aa53cf469cec5af62251b24abb"
         );
         assert_snapshot!(build.wheel_contents.join("\n"), @r"
         built_by_uv-0.1.0.data/data/
@@ -673,7 +682,7 @@ mod tests {
             .unwrap()
             .read_to_string(&mut record)
             .unwrap();
-        assert_snapshot!(record, @r###"
+        assert_snapshot!(record, @r"
         built_by_uv/__init__.py,sha256=AJ7XpTNWxYktP97ydb81UpnNqoebH7K4sHRakAMQKG4,44
         built_by_uv/arithmetic/__init__.py,sha256=x2agwFbJAafc9Z6TdJ0K6b6bLMApQdvRSQjP4iy7IEI,67
         built_by_uv/arithmetic/circle.py,sha256=FYZkv6KwrF9nJcwGOKigjke1dm1Fkie7qW1lWJoh3AE,287
@@ -685,11 +694,11 @@ mod tests {
         built_by_uv-0.1.0.data/headers/built_by_uv.h,sha256=p5-HBunJ1dY-xd4dMn03PnRClmGyRosScIp8rT46kg4,144
         built_by_uv-0.1.0.data/scripts/whoami.sh,sha256=T2cmhuDFuX-dTkiSkuAmNyIzvv8AKopjnuTCcr9o-eE,20
         built_by_uv-0.1.0.data/data/data.csv,sha256=7z7u-wXu7Qr2eBZFVpBILlNUiGSngv_1vYqZHVWOU94,265
-        built_by_uv-0.1.0.dist-info/WHEEL,sha256=PaG_oOj9G2zCRqoLK0SjWBVZbGAMtIXDmm-MEGw9Wo0,83
+        built_by_uv-0.1.0.dist-info/WHEEL,sha256=JBpLtoa_WBz5WPGpRsAUTD4Dz6H0KkkdiKWCkfMSS1U,84
         built_by_uv-0.1.0.dist-info/entry_points.txt,sha256=-IO6yaq6x6HSl-zWH96rZmgYvfyHlH00L5WQoCpz-YI,50
         built_by_uv-0.1.0.dist-info/METADATA,sha256=m6EkVvKrGmqx43b_VR45LHD37IZxPYC0NI6Qx9_UXLE,474
         built_by_uv-0.1.0.dist-info/RECORD,,
-        "###);
+        ");
     }
 
     /// Test that `license = { file = "LICENSE" }` is supported.
@@ -738,6 +747,7 @@ mod tests {
             output_dir.path(),
             None,
             "0.5.15",
+            Preview::default(),
         )
         .unwrap();
         let wheel = output_dir
@@ -790,7 +800,13 @@ mod tests {
 
         // Prepare the metadata.
         let metadata_dir = TempDir::new().unwrap();
-        let dist_info_dir = metadata(src.path(), metadata_dir.path(), "0.5.15").unwrap();
+        let dist_info_dir = metadata(
+            src.path(),
+            metadata_dir.path(),
+            "0.5.15",
+            Preview::default(),
+        )
+        .unwrap();
         let metadata_prepared =
             fs_err::read_to_string(metadata_dir.path().join(&dist_info_dir).join("METADATA"))
                 .unwrap();
@@ -802,6 +818,7 @@ mod tests {
             output_dir.path(),
             Some(&metadata_dir.path().join(&dist_info_dir)),
             "0.5.15",
+            Preview::default(),
         )
         .unwrap();
         let wheel = output_dir
@@ -851,7 +868,7 @@ mod tests {
         File::create(src.path().join("two_step_build").join("__init__.py")).unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build1 = build(src.path(), dist.path()).unwrap();
+        let build1 = build(src.path(), dist.path(), Preview::default()).unwrap();
 
         assert_snapshot!(build1.source_dist_contents.join("\n"), @r"
         two_step_build-1.0.0/
@@ -890,7 +907,7 @@ mod tests {
         .unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build2 = build(src.path(), dist.path()).unwrap();
+        let build2 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_eq!(build1, build2);
     }
 
@@ -917,7 +934,7 @@ mod tests {
         File::create(src.path().join("src").join("camelCase").join("__init__.py")).unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build1 = build(src.path(), dist.path()).unwrap();
+        let build1 = build(src.path(), dist.path(), Preview::default()).unwrap();
 
         assert_snapshot!(build1.wheel_contents.join("\n"), @r"
         camelCase/
@@ -934,7 +951,7 @@ mod tests {
             pyproject_toml.replace("camelCase", "camel_case"),
         )
         .unwrap();
-        let build_err = build(src.path(), dist.path()).unwrap_err();
+        let build_err = build(src.path(), dist.path(), Preview::default()).unwrap_err();
         let err_message = format_err(&build_err)
             .replace(&src.path().user_display().to_string(), "[TEMP_PATH]")
             .replace('\\', "/");
@@ -963,7 +980,7 @@ mod tests {
         fs_err::write(src.path().join("pyproject.toml"), pyproject_toml).unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build_err = build(src.path(), dist.path()).unwrap_err();
+        let build_err = build(src.path(), dist.path(), Preview::default()).unwrap_err();
         let err_message = format_err(&build_err);
         assert_snapshot!(
             err_message,
@@ -999,7 +1016,7 @@ mod tests {
         File::create(&regular_init_py).unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build_err = build(src.path(), dist.path()).unwrap_err();
+        let build_err = build(src.path(), dist.path(), Preview::default()).unwrap_err();
         let err_message = format_err(&build_err)
             .replace(&src.path().user_display().to_string(), "[TEMP_PATH]")
             .replace('\\', "/");
@@ -1018,7 +1035,7 @@ mod tests {
         )
         .unwrap();
 
-        let build1 = build(src.path(), dist.path()).unwrap();
+        let build1 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_snapshot!(build1.wheel_contents.join("\n"), @r"
         stuffed_bird-stubs/
         stuffed_bird-stubs/__init__.pyi
@@ -1044,7 +1061,7 @@ mod tests {
         };
         fs_err::write(src.path().join("pyproject.toml"), pyproject_toml).unwrap();
 
-        let build2 = build(src.path(), dist.path()).unwrap();
+        let build2 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_eq!(build1.wheel_contents, build2.wheel_contents);
     }
 
@@ -1098,7 +1115,7 @@ mod tests {
         fs_err::remove_file(bogus_init_py).unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build1 = build(src.path(), dist.path()).unwrap();
+        let build1 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_snapshot!(build1.source_dist_contents.join("\n"), @r"
         simple_namespace_part-1.0.0/
         simple_namespace_part-1.0.0/PKG-INFO
@@ -1135,7 +1152,7 @@ mod tests {
         };
         fs_err::write(src.path().join("pyproject.toml"), pyproject_toml).unwrap();
 
-        let build2 = build(src.path(), dist.path()).unwrap();
+        let build2 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_eq!(build1, build2);
     }
 
@@ -1189,7 +1206,7 @@ mod tests {
         .unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build1 = build(src.path(), dist.path()).unwrap();
+        let build1 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_snapshot!(build1.wheel_contents.join("\n"), @r"
         complex_namespace-1.0.0.dist-info/
         complex_namespace-1.0.0.dist-info/METADATA
@@ -1219,7 +1236,7 @@ mod tests {
         };
         fs_err::write(src.path().join("pyproject.toml"), pyproject_toml).unwrap();
 
-        let build2 = build(src.path(), dist.path()).unwrap();
+        let build2 = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_eq!(build1, build2);
     }
 
@@ -1260,7 +1277,7 @@ mod tests {
         .unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build = build(src.path(), dist.path()).unwrap();
+        let build = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_snapshot!(build.wheel_contents.join("\n"), @r"
         cloud-stubs/
         cloud-stubs/db/
@@ -1357,7 +1374,7 @@ mod tests {
         fs_err::remove_file(bogus_init_py).unwrap();
 
         let dist = TempDir::new().unwrap();
-        let build = build(src.path(), dist.path()).unwrap();
+        let build = build(src.path(), dist.path(), Preview::default()).unwrap();
         assert_snapshot!(build.source_dist_contents.join("\n"), @r"
         simple_namespace_part-1.0.0/
         simple_namespace_part-1.0.0/PKG-INFO
@@ -1385,4 +1402,51 @@ mod tests {
         simple_namespace_part-1.0.0.dist-info/WHEEL
         ");
     }
+
+    /// Check that JSON metadata files are present.
+    #[test]
+    fn metadata_json_preview() {
+        let src = TempDir::new().unwrap();
+        fs_err::write(
+            src.path().join("pyproject.toml"),
+            indoc! {r#"
+            [project]
+            name = "metadata-json-preview"
+            version = "1.0.0"
+
+            [build-system]
+            requires = ["uv_build>=0.5.15,<0.6.0"]
+            build-backend = "uv_build"
+        "#
+            },
+        )
+        .unwrap();
+        fs_err::create_dir_all(src.path().join("src").join("metadata_json_preview")).unwrap();
+        File::create(
+            src.path()
+                .join("src")
+                .join("metadata_json_preview")
+                .join("__init__.py"),
+        )
+        .unwrap();
+
+        let dist = TempDir::new().unwrap();
+        let build = build(
+            src.path(),
+            dist.path(),
+            Preview::new(PreviewFeatures::METADATA_JSON),
+        )
+        .unwrap();
+
+        assert_snapshot!(build.wheel_contents.join("\n"), @r"
+        metadata_json_preview-1.0.0.dist-info/
+        metadata_json_preview-1.0.0.dist-info/METADATA
+        metadata_json_preview-1.0.0.dist-info/METADATA.json
+        metadata_json_preview-1.0.0.dist-info/RECORD
+        metadata_json_preview-1.0.0.dist-info/WHEEL
+        metadata_json_preview-1.0.0.dist-info/WHEEL.json
+        metadata_json_preview/
+        metadata_json_preview/__init__.py
+        ");
+    }
 }

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

@@ -1,9 +1,9 @@
 use base64::{Engine, prelude::BASE64_URL_SAFE_NO_PAD as base64};
 use fs_err::File;
 use globset::{GlobSet, GlobSetBuilder};
-use itertools::Itertools;
 use rustc_hash::FxHashSet;
 use sha2::{Digest, Sha256};
+use std::fmt::{Display, Formatter};
 use std::io::{BufReader, Read, Write};
 use std::path::{Path, PathBuf};
 use std::{io, mem};
@@ -15,6 +15,7 @@ use uv_distribution_filename::WheelFilename;
 use uv_fs::Simplified;
 use uv_globfilter::{GlobDirFilter, PortableGlobParser};
 use uv_platform_tags::{AbiTag, LanguageTag, PlatformTag};
+use uv_preview::{Preview, PreviewFeatures};
 use uv_warnings::warn_user_once;
 
 use crate::metadata::DEFAULT_EXCLUDES;
@@ -28,6 +29,7 @@ pub fn build_wheel(
     wheel_dir: &Path,
     metadata_directory: Option<&Path>,
     uv_version: &str,
+    preview: Preview,
 ) -> Result<WheelFilename, Error> {
     let contents = fs_err::read_to_string(source_tree.join("pyproject.toml"))?;
     let pyproject_toml = PyProjectToml::parse(&contents)?;
@@ -57,6 +59,7 @@ pub fn build_wheel(
         &filename,
         uv_version,
         wheel_writer,
+        preview,
     )?;
 
     Ok(filename)
@@ -66,6 +69,7 @@ pub fn build_wheel(
 pub fn list_wheel(
     source_tree: &Path,
     uv_version: &str,
+    preview: Preview,
 ) -> Result<(WheelFilename, FileList), Error> {
     let contents = fs_err::read_to_string(source_tree.join("pyproject.toml"))?;
     let pyproject_toml = PyProjectToml::parse(&contents)?;
@@ -86,7 +90,14 @@ pub fn list_wheel(
 
     let mut files = FileList::new();
     let writer = ListWriter::new(&mut files);
-    write_wheel(source_tree, &pyproject_toml, &filename, uv_version, writer)?;
+    write_wheel(
+        source_tree,
+        &pyproject_toml,
+        &filename,
+        uv_version,
+        writer,
+        preview,
+    )?;
     Ok((filename, files))
 }
 
@@ -96,6 +107,7 @@ fn write_wheel(
     filename: &WheelFilename,
     uv_version: &str,
     mut wheel_writer: impl DirectoryWriter,
+    preview: Preview,
 ) -> Result<(), Error> {
     let settings = pyproject_toml
         .settings()
@@ -231,6 +243,7 @@ fn write_wheel(
         filename,
         source_tree,
         uv_version,
+        preview,
     )?;
     wheel_writer.close(&dist_info_dir)?;
 
@@ -243,6 +256,7 @@ pub fn build_editable(
     wheel_dir: &Path,
     metadata_directory: Option<&Path>,
     uv_version: &str,
+    preview: Preview,
 ) -> Result<WheelFilename, Error> {
     let contents = fs_err::read_to_string(source_tree.join("pyproject.toml"))?;
     let pyproject_toml = PyProjectToml::parse(&contents)?;
@@ -293,6 +307,7 @@ pub fn build_editable(
         &filename,
         source_tree,
         uv_version,
+        preview,
     )?;
     wheel_writer.close(&dist_info_dir)?;
 
@@ -304,6 +319,7 @@ pub fn metadata(
     source_tree: &Path,
     metadata_directory: &Path,
     uv_version: &str,
+    preview: Preview,
 ) -> Result<String, Error> {
     let contents = fs_err::read_to_string(source_tree.join("pyproject.toml"))?;
     let pyproject_toml = PyProjectToml::parse(&contents)?;
@@ -333,6 +349,7 @@ pub fn metadata(
         &filename,
         source_tree,
         uv_version,
+        preview,
     )?;
     wheel_writer.close(&dist_info_dir)?;
 
@@ -535,6 +552,7 @@ fn write_dist_info(
     filename: &WheelFilename,
     root: &Path,
     uv_version: &str,
+    preview: Preview,
 ) -> Result<String, Error> {
     let dist_info_dir = format!(
         "{}-{}.dist-info",
@@ -544,9 +562,18 @@ fn write_dist_info(
 
     writer.write_directory(&dist_info_dir)?;
 
-    // Add `WHEEL`.
+    // Add `WHEEL` and `WHEEL.json`.
-    let wheel_info = wheel_info(filename, uv_version);
+    let wheel_info = WheelInfo::new(filename, uv_version);
-    writer.write_bytes(&format!("{dist_info_dir}/WHEEL"), wheel_info.as_bytes())?;
+    writer.write_bytes(
+        &format!("{dist_info_dir}/WHEEL"),
+        wheel_info.to_string().as_bytes(),
+    )?;
+    if preview.is_enabled(PreviewFeatures::METADATA_JSON) {
+        writer.write_bytes(
+            &format!("{dist_info_dir}/WHEEL.json"),
+            &serde_json::to_vec(&wheel_info).map_err(Error::Json)?,
+        )?;
+    }
 
     // Add `entry_points.txt`.
     if let Some(entrypoint) = pyproject_toml.to_entry_points()? {
@@ -556,34 +583,64 @@ fn write_dist_info(
         )?;
     }
 
-    // Add `METADATA`.
+    // Add `METADATA` and `METADATA.json`.
-    let metadata = pyproject_toml.to_metadata(root)?.core_metadata_format();
+    let metadata = pyproject_toml.to_metadata(root)?;
-    writer.write_bytes(&format!("{dist_info_dir}/METADATA"), metadata.as_bytes())?;
+    writer.write_bytes(
+        &format!("{dist_info_dir}/METADATA"),
+        metadata.core_metadata_format().as_bytes(),
+    )?;
+    if preview.is_enabled(PreviewFeatures::METADATA_JSON) {
+        writer.write_bytes(
+            &format!("{dist_info_dir}/METADATA.json"),
+            &serde_json::to_vec(&metadata).map_err(Error::Json)?,
+        )?;
+    }
 
     // `RECORD` is added on closing.
 
     Ok(dist_info_dir)
 }
 
-/// Returns the `WHEEL` file contents.
+/// The contents of the `WHEEL` and `WHEEL.json` files.
-fn wheel_info(filename: &WheelFilename, uv_version: &str) -> String {
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
-    // https://packaging.python.org/en/latest/specifications/binary-distribution-format/#file-contents
+#[serde(rename_all = "kebab-case")]
-    let mut wheel_info = vec![
+struct WheelInfo {
-        ("Wheel-Version", "1.0".to_string()),
+    wheel_version: String,
-        ("Generator", format!("uv {uv_version}")),
+    generator: String,
-        ("Root-Is-Purelib", "true".to_string()),
+    root_is_purelib: bool,
-    ];
+    tags: Vec<String>,
+}
+
+impl WheelInfo {
+    fn new(filename: &WheelFilename, uv_version: &str) -> Self {
+        let mut tags = Vec::new();
         for python_tag in filename.python_tags() {
             for abi_tag in filename.abi_tags() {
                 for platform_tag in filename.platform_tags() {
-                wheel_info.push(("Tag", format!("{python_tag}-{abi_tag}-{platform_tag}")));
+                    tags.push(format!("{python_tag}-{abi_tag}-{platform_tag}"));
                 }
             }
         }
-    wheel_info
+        Self {
-        .into_iter()
+            wheel_version: "1.0".to_string(),
-        .map(|(key, value)| format!("{key}: {value}"))
+            generator: format!("uv {uv_version}"),
-        .join("\n")
+            root_is_purelib: true,
+            tags,
+        }
+    }
+}
+
+impl Display for WheelInfo {
+    /// Returns the `WHEEL` file contents in its key-value format.
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        writeln!(f, "Wheel-Version: {}", self.wheel_version)?;
+        writeln!(f, "Generator: {}", self.generator)?;
+        writeln!(f, "Root-Is-Purelib: {}", self.root_is_purelib)?;
+        for tag in &self.tags {
+            writeln!(f, "Tag: {tag}")?;
+        }
+        Ok(())
+    }
 }
 
 /// Zip archive (wheel) writer.
@@ -784,7 +841,7 @@ mod test {
             PlatformTag::Any,
         );
 
-        assert_snapshot!(wheel_info(&filename, "1.0.0+test"), @r"
+        assert_snapshot!(WheelInfo::new(&filename, "1.0.0+test").to_string(), @r"
         Wheel-Version: 1.0
         Generator: uv 1.0.0+test
         Root-Is-Purelib: true
@@ -813,7 +870,13 @@ mod test {
     fn test_prepare_metadata() {
         let metadata_dir = TempDir::new().unwrap();
         let built_by_uv = Path::new("../../scripts/packages/built-by-uv");
-        metadata(built_by_uv, metadata_dir.path(), "1.0.0+test").unwrap();
+        metadata(
+            built_by_uv,
+            metadata_dir.path(),
+            "1.0.0+test",
+            Preview::default(),
+        )
+        .unwrap();
 
         let mut files: Vec<_> = WalkDir::new(metadata_dir.path())
             .sort_by_file_name()
@@ -861,12 +924,12 @@ mod test {
         let record_file = metadata_dir
             .path()
             .join("built_by_uv-0.1.0.dist-info/RECORD");
-        assert_snapshot!(fs_err::read_to_string(record_file).unwrap(), @r###"
+        assert_snapshot!(fs_err::read_to_string(record_file).unwrap(), @r"
-        built_by_uv-0.1.0.dist-info/WHEEL,sha256=PaG_oOj9G2zCRqoLK0SjWBVZbGAMtIXDmm-MEGw9Wo0,83
+        built_by_uv-0.1.0.dist-info/WHEEL,sha256=JBpLtoa_WBz5WPGpRsAUTD4Dz6H0KkkdiKWCkfMSS1U,84
         built_by_uv-0.1.0.dist-info/entry_points.txt,sha256=-IO6yaq6x6HSl-zWH96rZmgYvfyHlH00L5WQoCpz-YI,50
         built_by_uv-0.1.0.dist-info/METADATA,sha256=m6EkVvKrGmqx43b_VR45LHD37IZxPYC0NI6Qx9_UXLE,474
         built_by_uv-0.1.0.dist-info/RECORD,,
-        "###);
+        ");
 
         let wheel_file = metadata_dir
             .path()

crates/uv-build/Cargo.toml

@@ -11,7 +11,9 @@ license = { workspace = true }
 
 [dependencies]
 uv-build-backend = { workspace = true }
+uv-preview = { workspace = true }
 uv-version = { workspace = true }
+uv-static = { workspace = true }
 
 anyhow = { workspace = true }
 

crates/uv-build/src/main.rs

@@ -2,6 +2,9 @@ use anyhow::{Context, Result, bail};
 use std::env;
 use std::io::Write;
 use std::path::PathBuf;
+use std::str::FromStr;
+use uv_preview::{Preview, PreviewFeatures};
+use uv_static::{EnvVars, parse_boolish_environment_variable};
 
 /// Entrypoint for the `uv-build` Python package.
 fn main() -> Result<()> {
@@ -15,6 +18,25 @@ fn main() -> Result<()> {
         .to_str()
         .context("Invalid non-UTF8 command")?
         .to_string();
+
+    // Ad-hoc preview features parsing due to a lack of clap CLI in uv-build.
+    let preview_features =
+        if parse_boolish_environment_variable(EnvVars::UV_PREVIEW)?.unwrap_or(false) {
+            PreviewFeatures::all()
+        } else if let Some(preview_features) = env::var_os(EnvVars::UV_PREVIEW_FEATURES) {
+            let preview_features = preview_features.to_str().with_context(|| {
+                format!("`{}` is not valid UTF-8", EnvVars::UV_PREVIEW_FEATURES)
+            })?;
+            PreviewFeatures::from_str(preview_features).with_context(|| {
+                format!(
+                    "Invalid preview features list in `{}`",
+                    EnvVars::UV_PREVIEW_FEATURES
+                )
+            })?
+        } else {
+            PreviewFeatures::default()
+        };
+    let preview = Preview::new(preview_features);
     match command.as_str() {
         "build-sdist" => {
             let sdist_directory = PathBuf::from(args.next().context("Missing sdist directory")?);
@@ -34,6 +56,7 @@ fn main() -> Result<()> {
                 &wheel_directory,
                 metadata_directory.as_deref(),
                 uv_version::version(),
+                preview,
             )?;
             // Tell the build frontend about the name of the artifact we built
             writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;
@@ -46,6 +69,7 @@ fn main() -> Result<()> {
                 &wheel_directory,
                 metadata_directory.as_deref(),
                 uv_version::version(),
+                preview,
             )?;
             // Tell the build frontend about the name of the artifact we built
             writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;
@@ -56,6 +80,7 @@ fn main() -> Result<()> {
                 &env::current_dir()?,
                 &wheel_directory,
                 uv_version::version(),
+                preview,
             )?;
             // Tell the build frontend about the name of the artifact we built
             writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;
@@ -66,6 +91,7 @@ fn main() -> Result<()> {
                 &env::current_dir()?,
                 &wheel_directory,
                 uv_version::version(),
+                preview,
             )?;
             // Tell the build frontend about the name of the artifact we built
             writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;

crates/uv-dispatch/src/lib.rs

@@ -523,6 +523,7 @@ impl BuildContext for BuildDispatch<'_> {
         debug!("Performing direct build for {identifier}");
 
         let output_dir = output_dir.to_path_buf();
+        let preview = self.preview;
         let filename = tokio::task::spawn_blocking(move || -> Result<_> {
             let filename = match build_kind {
                 BuildKind::Wheel => {
@@ -531,6 +532,7 @@ impl BuildContext for BuildDispatch<'_> {
                         &output_dir,
                         None,
                         uv_version::version(),
+                        preview,
                     )?;
                     DistFilename::WheelFilename(wheel)
                 }
@@ -548,6 +550,7 @@ impl BuildContext for BuildDispatch<'_> {
                         &output_dir,
                         None,
                         uv_version::version(),
+                        preview,
                     )?;
                     DistFilename::WheelFilename(wheel)
                 }

crates/uv-preview/src/lib.rs

@@ -18,6 +18,7 @@ bitflags::bitflags! {
         const EXTRA_BUILD_DEPENDENCIES = 1 << 6;
         const DETECT_MODULE_CONFLICTS = 1 << 7;
         const FORMAT = 1 << 8;
+        const METADATA_JSON = 1 << 9;
     }
 }
 
@@ -36,6 +37,7 @@ impl PreviewFeatures {
             Self::EXTRA_BUILD_DEPENDENCIES => "extra-build-dependencies",
             Self::DETECT_MODULE_CONFLICTS => "detect-module-conflicts",
             Self::FORMAT => "format",
+            Self::METADATA_JSON => "metadata-json",
             _ => panic!("`flag_as_str` can only be used for exactly one feature flag"),
         }
     }
@@ -82,6 +84,7 @@ impl FromStr for PreviewFeatures {
                 "extra-build-dependencies" => Self::EXTRA_BUILD_DEPENDENCIES,
                 "detect-module-conflicts" => Self::DETECT_MODULE_CONFLICTS,
                 "format" => Self::FORMAT,
+                "metadata-json" => Self::METADATA_JSON,
                 _ => {
                     warn_user_once!("Unknown preview feature: `{part}`");
                     continue;
@@ -257,6 +260,10 @@ mod tests {
             "detect-module-conflicts"
         );
         assert_eq!(PreviewFeatures::FORMAT.flag_as_str(), "format");
+        assert_eq!(
+            PreviewFeatures::METADATA_JSON.flag_as_str(),
+            "metadata-json"
+        );
     }
 
     #[test]

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

@@ -10,7 +10,8 @@ use crate::metadata::Headers;
 
 /// Code Metadata 2.3 as specified in
 /// <https://packaging.python.org/specifications/core-metadata/>.
-#[derive(Debug, Clone, Default, PartialEq, Eq)]
+#[derive(Debug, Clone, Default, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "kebab-case")]
 pub struct Metadata23 {
     /// Version of the file format; legal values are `1.0`, `1.1`, `1.2`, `2.1`, `2.2`, `2.3` and
     /// `2.4`.

crates/uv-settings/src/lib.rs

@@ -3,7 +3,7 @@ use std::path::{Path, PathBuf};
 
 use uv_dirs::{system_config_file, user_config_dir};
 use uv_fs::Simplified;
-use uv_static::EnvVars;
+use uv_static::{EnvVars, InvalidEnvironmentVariable, parse_boolish_environment_variable};
 use uv_warnings::warn_user;
 
 pub use crate::combine::*;
@@ -554,12 +554,8 @@ pub enum Error {
     #[error("Failed to parse: `{}`. The `{}` field is not allowed in a `uv.toml` file. `{}` is only applicable in the context of a project, and should be placed in a `pyproject.toml` file instead.", _0.user_display(), _1, _1)]
     PyprojectOnlyField(PathBuf, &'static str),
 
-    #[error("Failed to parse environment variable `{name}` with invalid value `{value}`: {err}")]
+    #[error(transparent)]
-    InvalidEnvironmentVariable {
+    InvalidEnvironmentVariable(#[from] InvalidEnvironmentVariable),
-        name: String,
-        value: String,
-        err: String,
-    },
 }
 
 /// Options loaded from environment variables.
@@ -583,55 +579,3 @@ impl EnvironmentOptions {
         })
     }
 }
-
-/// Parse a boolean environment variable.
-///
-/// Adapted from Clap's `BoolishValueParser` which is dual licensed under the MIT and Apache-2.0.
-fn parse_boolish_environment_variable(name: &'static str) -> Result<Option<bool>, Error> {
-    // See `clap_builder/src/util/str_to_bool.rs`
-    // We want to match Clap's accepted values
-
-    // True values are `y`, `yes`, `t`, `true`, `on`, and `1`.
-    const TRUE_LITERALS: [&str; 6] = ["y", "yes", "t", "true", "on", "1"];
-
-    // False values are `n`, `no`, `f`, `false`, `off`, and `0`.
-    const FALSE_LITERALS: [&str; 6] = ["n", "no", "f", "false", "off", "0"];
-
-    // Converts a string literal representation of truth to true or false.
-    //
-    // `false` values are `n`, `no`, `f`, `false`, `off`, and `0` (case insensitive).
-    //
-    // Any other value will be considered as `true`.
-    fn str_to_bool(val: impl AsRef<str>) -> Option<bool> {
-        let pat: &str = &val.as_ref().to_lowercase();
-        if TRUE_LITERALS.contains(&pat) {
-            Some(true)
-        } else if FALSE_LITERALS.contains(&pat) {
-            Some(false)
-        } else {
-            None
-        }
-    }
-
-    let Some(value) = std::env::var_os(name) else {
-        return Ok(None);
-    };
-
-    let Some(value) = value.to_str() else {
-        return Err(Error::InvalidEnvironmentVariable {
-            name: name.to_string(),
-            value: value.to_string_lossy().to_string(),
-            err: "expected a valid UTF-8 string".to_string(),
-        });
-    };
-
-    let Some(value) = str_to_bool(value) else {
-        return Err(Error::InvalidEnvironmentVariable {
-            name: name.to_string(),
-            value: value.to_string(),
-            err: "expected a boolish value".to_string(),
-        });
-    };
-
-    Ok(Some(value))
-}

crates/uv-static/Cargo.toml

@@ -17,3 +17,5 @@ workspace = true
 
 [dependencies]
 uv-macros = { workspace = true }
+
+thiserror = { workspace = true }

crates/uv-static/src/lib.rs

@@ -1,3 +1,67 @@
 pub use env_vars::*;
 
 mod env_vars;
+
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+#[error("Failed to parse environment variable `{name}` with invalid value `{value}`: {err}")]
+pub struct InvalidEnvironmentVariable {
+    name: String,
+    value: String,
+    err: String,
+}
+
+/// Parse a boolean environment variable.
+///
+/// Adapted from Clap's `BoolishValueParser` which is dual licensed under the MIT and Apache-2.0.
+pub fn parse_boolish_environment_variable(
+    name: &'static str,
+) -> Result<Option<bool>, InvalidEnvironmentVariable> {
+    // See `clap_builder/src/util/str_to_bool.rs`
+    // We want to match Clap's accepted values
+
+    // True values are `y`, `yes`, `t`, `true`, `on`, and `1`.
+    const TRUE_LITERALS: [&str; 6] = ["y", "yes", "t", "true", "on", "1"];
+
+    // False values are `n`, `no`, `f`, `false`, `off`, and `0`.
+    const FALSE_LITERALS: [&str; 6] = ["n", "no", "f", "false", "off", "0"];
+
+    // Converts a string literal representation of truth to true or false.
+    //
+    // `false` values are `n`, `no`, `f`, `false`, `off`, and `0` (case insensitive).
+    //
+    // Any other value will be considered as `true`.
+    fn str_to_bool(val: impl AsRef<str>) -> Option<bool> {
+        let pat: &str = &val.as_ref().to_lowercase();
+        if TRUE_LITERALS.contains(&pat) {
+            Some(true)
+        } else if FALSE_LITERALS.contains(&pat) {
+            Some(false)
+        } else {
+            None
+        }
+    }
+
+    let Some(value) = std::env::var_os(name) else {
+        return Ok(None);
+    };
+
+    let Some(value) = value.to_str() else {
+        return Err(InvalidEnvironmentVariable {
+            name: name.to_string(),
+            value: value.to_string_lossy().to_string(),
+            err: "expected a valid UTF-8 string".to_string(),
+        });
+    };
+
+    let Some(value) = str_to_bool(value) else {
+        return Err(InvalidEnvironmentVariable {
+            name: name.to_string(),
+            value: value.to_string(),
+            err: "expected a boolish value".to_string(),
+        });
+    };
+
+    Ok(Some(value))
+}

crates/uv/src/commands/build_backend.rs

@@ -3,6 +3,7 @@ use anyhow::{Context, Result};
 use std::env;
 use std::io::Write;
 use std::path::Path;
+use uv_preview::Preview;
 
 /// PEP 517 hook to build a source distribution.
 pub(crate) fn build_sdist(sdist_directory: &Path) -> Result<ExitStatus> {
@@ -20,12 +21,14 @@ pub(crate) fn build_sdist(sdist_directory: &Path) -> Result<ExitStatus> {
 pub(crate) fn build_wheel(
     wheel_directory: &Path,
     metadata_directory: Option<&Path>,
+    preview: Preview,
 ) -> Result<ExitStatus> {
     let filename = uv_build_backend::build_wheel(
         &env::current_dir()?,
         wheel_directory,
         metadata_directory,
         uv_version::version(),
+        preview,
     )?;
     // Tell the build frontend about the name of the artifact we built
     writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;
@@ -36,12 +39,14 @@ pub(crate) fn build_wheel(
 pub(crate) fn build_editable(
     wheel_directory: &Path,
     metadata_directory: Option<&Path>,
+    preview: Preview,
 ) -> Result<ExitStatus> {
     let filename = uv_build_backend::build_editable(
         &env::current_dir()?,
         wheel_directory,
         metadata_directory,
         uv_version::version(),
+        preview,
     )?;
     // Tell the build frontend about the name of the artifact we built
     writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;
@@ -59,11 +64,15 @@ pub(crate) fn get_requires_for_build_wheel() -> Result<ExitStatus> {
 }
 
 /// PEP 517 hook to just emit metadata through `.dist-info`.
-pub(crate) fn prepare_metadata_for_build_wheel(metadata_directory: &Path) -> Result<ExitStatus> {
+pub(crate) fn prepare_metadata_for_build_wheel(
+    metadata_directory: &Path,
+    preview: Preview,
+) -> Result<ExitStatus> {
     let filename = uv_build_backend::metadata(
         &env::current_dir()?,
         metadata_directory,
         uv_version::version(),
+        preview,
     )?;
     // Tell the build frontend about the name of the artifact we built
     writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;
@@ -76,11 +85,15 @@ pub(crate) fn get_requires_for_build_editable() -> Result<ExitStatus> {
 }
 
 /// PEP 660 hook to just emit metadata through `.dist-info`.
-pub(crate) fn prepare_metadata_for_build_editable(metadata_directory: &Path) -> Result<ExitStatus> {
+pub(crate) fn prepare_metadata_for_build_editable(
+    metadata_directory: &Path,
+    preview: Preview,
+) -> Result<ExitStatus> {
     let filename = uv_build_backend::metadata(
         &env::current_dir()?,
         metadata_directory,
         uv_version::version(),
+        preview,
     )?;
     // Tell the build frontend about the name of the artifact we built
     writeln!(&mut std::io::stdout(), "{filename}").context("stdout is closed")?;

crates/uv/src/commands/build_frontend.rs

@@ -729,6 +729,7 @@ async fn build_package(
                 version_id,
                 build_output,
                 Some(sdist_build.normalized_filename().version()),
+                preview,
             )
             .await?;
             build_results.push(wheel_build);
@@ -766,6 +767,7 @@ async fn build_package(
                 version_id,
                 build_output,
                 None,
+                preview,
             )
             .await?;
             build_results.push(wheel_build);
@@ -801,6 +803,7 @@ async fn build_package(
                 version_id,
                 build_output,
                 Some(sdist_build.normalized_filename().version()),
+                preview,
             )
             .await?;
             build_results.push(sdist_build);
@@ -844,6 +847,7 @@ async fn build_package(
                 version_id,
                 build_output,
                 version.as_ref(),
+                preview,
             )
             .await?;
             build_results.push(wheel_build);
@@ -996,12 +1000,13 @@ async fn build_wheel(
     build_output: BuildOutput,
     // Used for checking version consistency
     version: Option<&Version>,
+    preview: Preview,
 ) -> Result<BuildMessage, Error> {
     let build_message = match action {
         BuildAction::List => {
             let source_tree_ = source_tree.to_path_buf();
             let (filename, file_list) = tokio::task::spawn_blocking(move || {
-                uv_build_backend::list_wheel(&source_tree_, uv_version::version())
+                uv_build_backend::list_wheel(&source_tree_, uv_version::version(), preview)
             })
             .await??;
             let raw_filename = filename.to_string();
@@ -1031,6 +1036,7 @@ async fn build_wheel(
                     &output_dir_,
                     None,
                     uv_version::version(),
+                    preview,
                 )
             })
             .await??;

crates/uv/src/lib.rs

@@ -1641,6 +1641,7 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
             } => commands::build_backend::build_wheel(
                 &wheel_directory,
                 metadata_directory.as_deref(),
+                globals.preview,
             ),
             BuildBackendCommand::BuildEditable {
                 wheel_directory,
@@ -1648,6 +1649,7 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
             } => commands::build_backend::build_editable(
                 &wheel_directory,
                 metadata_directory.as_deref(),
+                globals.preview,
             ),
             BuildBackendCommand::GetRequiresForBuildSdist => {
                 commands::build_backend::get_requires_for_build_sdist()
@@ -1656,13 +1658,19 @@ async fn run(mut cli: Cli) -> Result<ExitStatus> {
                 commands::build_backend::get_requires_for_build_wheel()
             }
             BuildBackendCommand::PrepareMetadataForBuildWheel { wheel_directory } => {
-                commands::build_backend::prepare_metadata_for_build_wheel(&wheel_directory)
+                commands::build_backend::prepare_metadata_for_build_wheel(
+                    &wheel_directory,
+                    globals.preview,
+                )
             }
             BuildBackendCommand::GetRequiresForBuildEditable => {
                 commands::build_backend::get_requires_for_build_editable()
             }
             BuildBackendCommand::PrepareMetadataForBuildEditable { wheel_directory } => {
-                commands::build_backend::prepare_metadata_for_build_editable(&wheel_directory)
+                commands::build_backend::prepare_metadata_for_build_editable(
+                    &wheel_directory,
+                    globals.preview,
+                )
             }
         })
         .await