Build backend: Fix pre-PEP 639 license files (#9965)

We were not copying the license file from a pre-PEP 639 declaration to
the source distribution.

Fixes #9947

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

@@ -180,9 +180,10 @@ mod tests {
     use super::*;
     use flate2::bufread::GzDecoder;
     use fs_err::File;
+    use indoc::indoc;
     use insta::assert_snapshot;
     use itertools::Itertools;
-    use std::io::BufReader;
+    use std::io::{BufReader, Read};
     use tempfile::TempDir;
     use uv_fs::{copy_dir_all, relative_to};
 
@@ -391,4 +392,73 @@ mod tests {
             fs_err::read(indirect_output_dir.path().join(wheel_filename)).unwrap()
         );
     }
+
+    /// Test that `license = { file = "LICENSE" }` is supported.
+    #[test]
+    fn license_file_pre_pep639() {
+        let src = TempDir::new().unwrap();
+        fs_err::write(
+            src.path().join("pyproject.toml"),
+            indoc! {r#"
+            [project]
+            name = "pep-pep639-license"
+            version = "1.0.0"
+            license = { file = "license.txt" }
+
+            [build-system]
+            requires = ["uv>=0.5.15,<0.6"]
+            build-backend = "uv"
+        "#
+            },
+        )
+        .unwrap();
+        fs_err::create_dir_all(src.path().join("src").join("pep_pep639_license")).unwrap();
+        File::create(
+            src.path()
+                .join("src")
+                .join("pep_pep639_license")
+                .join("__init__.py"),
+        )
+        .unwrap();
+        fs_err::write(
+            src.path().join("license.txt"),
+            "Copy carefully.\nSincerely, the authors",
+        )
+        .unwrap();
+
+        // Build a wheel from a source distribution
+        let output_dir = TempDir::new().unwrap();
+        build_source_dist(src.path(), output_dir.path(), "0.5.15").unwrap();
+        let sdist_tree = TempDir::new().unwrap();
+        let source_dist_path = output_dir.path().join("pep_pep639_license-1.0.0.tar.gz");
+        let sdist_reader = BufReader::new(File::open(&source_dist_path).unwrap());
+        let mut source_dist = tar::Archive::new(GzDecoder::new(sdist_reader));
+        source_dist.unpack(sdist_tree.path()).unwrap();
+        build_wheel(
+            &sdist_tree.path().join("pep_pep639_license-1.0.0"),
+            output_dir.path(),
+            None,
+            "0.5.15",
+        )
+        .unwrap();
+        let wheel = output_dir
+            .path()
+            .join("pep_pep639_license-1.0.0-py3-none-any.whl");
+        let mut wheel = zip::ZipArchive::new(File::open(wheel).unwrap()).unwrap();
+
+        let mut metadata = String::new();
+        wheel
+            .by_name("pep_pep639_license-1.0.0.dist-info/METADATA")
+            .unwrap()
+            .read_to_string(&mut metadata)
+            .unwrap();
+
+        assert_snapshot!(metadata, @r###"
+        Metadata-Version: 2.3
+        Name: pep-pep639-license
+        Version: 1.0.0
+        License: Copy carefully.
+                 Sincerely, the authors
+        "###);
+    }
 }

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

@@ -119,8 +119,31 @@ impl PyProjectToml {
         self.project.readme.as_ref()
     }
 
-    pub(crate) fn license_files(&self) -> Option<&[String]> {
-        self.project.license_files.as_deref()
+    /// The license files that need to be included in the source distribution.
+    pub(crate) fn license_files_source_dist(&self) -> impl Iterator<Item = &str> {
+        let license_file = self
+            .project
+            .license
+            .as_ref()
+            .and_then(|license| license.file())
+            .into_iter();
+        let license_files = self
+            .project
+            .license_files
+            .iter()
+            .flatten()
+            .map(String::as_str);
+        license_files.chain(license_file)
+    }
+
+    /// The license files that need to be included in the wheel.
+    pub(crate) fn license_files_wheel(&self) -> impl Iterator<Item = &str> {
+        // The pre-PEP 639 `license = { file = "..." }` is included inline in `METADATA`.
+        self.project
+            .license_files
+            .iter()
+            .flatten()
+            .map(String::as_str)
     }
 
     pub(crate) fn settings(&self) -> Option<&BuildBackendSettings> {
@@ -682,10 +705,20 @@ pub(crate) enum License {
     },
     File {
         /// The file containing the license text.
-        file: PathBuf,
+        file: String,
     },
 }
 
+impl License {
+    fn file(&self) -> Option<&str> {
+        if let Self::File { file } = self {
+            Some(file)
+        } else {
+            None
+        }
+    }
+}
+
 /// A `project.authors` or `project.maintainers` entry as specified in
 /// <https://packaging.python.org/en/latest/specifications/pyproject-toml/#authors-maintainers>.
 ///

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

@@ -95,7 +95,7 @@ fn source_dist_matcher(
     }
 
     // Include the license files
-    for license_files in pyproject_toml.license_files().into_iter().flatten() {
+    for license_files in pyproject_toml.license_files_source_dist() {
         trace!("Including license files at: `{license_files}`");
         let glob = parse_portable_glob(license_files).map_err(|err| Error::PortableGlob {
             field: "project.license-files".to_string(),

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

@@ -175,7 +175,7 @@ fn write_wheel(
     debug!("Visited {files_visited} files for wheel build");
 
     // Add the license files
-    if let Some(license_files) = &pyproject_toml.license_files() {
+    if pyproject_toml.license_files_wheel().next().is_some() {
         debug!("Adding license files");
         let license_dir = format!(
             "{}-{}.dist-info/licenses/",
@@ -186,7 +186,7 @@ fn write_wheel(
         wheel_subdir_from_globs(
             source_tree,
             &license_dir,
-            license_files,
+            pyproject_toml.license_files_wheel(),
             &mut wheel_writer,
             "project.license-files",
         )?;
@@ -429,14 +429,15 @@ pub(crate) fn build_exclude_matcher(
 fn wheel_subdir_from_globs(
     src: &Path,
     target: &str,
-    globs: &[String],
+    globs: impl IntoIterator<Item = impl AsRef<str>>,
     wheel_writer: &mut impl DirectoryWriter,
     // For error messages
     globs_field: &str,
 ) -> Result<(), Error> {
     let license_files_globs: Vec<_> = globs
-        .iter()
+        .into_iter()
         .map(|license_files| {
+            let license_files = license_files.as_ref();
             trace!(
                 "Including {} at `{}` with `{}`",
                 globs_field,