Make .egg-info filename parsing spec compliant (#4533)

## Summary

It turns out that `.egg-info` files and directories can _both_ have up
to four segments in the filename:
https://setuptools.pypa.io/en/latest/deprecated/python_eggs.html#filename-embedded-metadata.
This PR upgrades the parsing and now uses the same parsing for files and
directories.

Closes https://github.com/astral-sh/uv/issues/4532.

crates/distribution-filename/src/egg.rs

@@ -0,0 +1,112 @@
+use std::str::FromStr;
+
+use thiserror::Error;
+
+use pep440_rs::{Version, VersionParseError};
+use uv_normalize::{InvalidNameError, PackageName};
+
+#[derive(Error, Debug)]
+pub enum EggInfoFilenameError {
+    #[error("The filename \"{0}\" does not end in `.egg-info`")]
+    InvalidExtension(String),
+    #[error("The `.egg-info` filename \"{0}\" is missing a package name")]
+    MissingPackageName(String),
+    #[error("The `.egg-info` filename \"{0}\" is missing a version")]
+    MissingVersion(String),
+    #[error("The `.egg-info` filename \"{0}\" has an invalid package name")]
+    InvalidPackageName(String, InvalidNameError),
+    #[error("The `.egg-info` filename \"{0}\" has an invalid version: {1}")]
+    InvalidVersion(String, VersionParseError),
+}
+
+/// A filename parsed from an `.egg-info` file or directory (e.g., `zstandard-0.22.0-py3.12.egg-info`).
+///
+/// An `.egg-info` filename can contain up to four components, as in:
+///
+/// ```text
+/// name ["-" version ["-py" pyver ["-" required_platform]]] "." ext
+/// ```
+///
+/// See: <https://setuptools.pypa.io/en/latest/deprecated/python_eggs.html#filename-embedded-metadata>
+#[derive(Debug, Clone)]
+pub struct EggInfoFilename {
+    pub name: PackageName,
+    pub version: Version,
+}
+
+impl EggInfoFilename {
+    /// Parse an `.egg-info` filename, requiring at least a name and version.
+    pub fn parse(stem: &str) -> Result<Self, EggInfoFilenameError> {
+        // pip uses the following regex:
+        // ```python
+        // EGG_NAME = re.compile(
+        //     r"""
+        //     (?P<name>[^-]+) (
+        //         -(?P<ver>[^-]+) (
+        //             -py(?P<pyver>[^-]+) (
+        //                 -(?P<plat>.+)
+        //             )?
+        //         )?
+        //     )?
+        //     """,
+        //     re.VERBOSE | re.IGNORECASE,
+        // ).match
+        // ```
+        let mut parts = stem.split('-');
+        let name = parts
+            .next()
+            .ok_or_else(|| EggInfoFilenameError::MissingPackageName(format!("{stem}.egg-info")))?;
+        let version = parts
+            .next()
+            .ok_or_else(|| EggInfoFilenameError::MissingVersion(format!("{stem}.egg-info")))?;
+        let name = PackageName::from_str(name)
+            .map_err(|e| EggInfoFilenameError::InvalidPackageName(format!("{stem}.egg-info"), e))?;
+        let version = Version::from_str(version)
+            .map_err(|e| EggInfoFilenameError::InvalidVersion(format!("{stem}.egg-info"), e))?;
+        Ok(Self { name, version })
+    }
+}
+
+impl FromStr for EggInfoFilename {
+    type Err = EggInfoFilenameError;
+
+    fn from_str(filename: &str) -> Result<Self, Self::Err> {
+        let stem = filename
+            .strip_suffix(".egg-info")
+            .ok_or_else(|| EggInfoFilenameError::InvalidExtension(filename.to_string()))?;
+        Self::parse(stem)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn egg_info_filename() {
+        let filename = "zstandard-0.22.0-py3.12-darwin.egg-info";
+        let parsed = EggInfoFilename::from_str(filename).unwrap();
+        assert_eq!(parsed.name.as_ref(), "zstandard");
+        assert_eq!(parsed.version.to_string(), "0.22.0");
+
+        let filename = "zstandard-0.22.0-py3.12.egg-info";
+        let parsed = EggInfoFilename::from_str(filename).unwrap();
+        assert_eq!(parsed.name.as_ref(), "zstandard");
+        assert_eq!(parsed.version.to_string(), "0.22.0");
+
+        let filename = "zstandard-0.22.0.egg-info";
+        let parsed = EggInfoFilename::from_str(filename).unwrap();
+        assert_eq!(parsed.name.as_ref(), "zstandard");
+        assert_eq!(parsed.version.to_string(), "0.22.0");
+    }
+
+    #[test]
+    fn egg_info_filename_missing_version() {
+        let filename = "zstandard.egg-info";
+        let err = EggInfoFilename::from_str(filename).unwrap_err();
+        assert_eq!(
+            err.to_string(),
+            "The `.egg-info` filename \"zstandard.egg-info\" is missing a version"
+        );
+    }
+}

crates/distribution-filename/src/lib.rs

@@ -4,10 +4,12 @@ use std::str::FromStr;
 use uv_normalize::PackageName;
 
 pub use build_tag::{BuildTag, BuildTagError};
+pub use egg::{EggInfoFilename, EggInfoFilenameError};
 pub use source_dist::{SourceDistExtension, SourceDistFilename, SourceDistFilenameError};
 pub use wheel::{WheelFilename, WheelFilenameError};
 
 mod build_tag;
+mod egg;
 mod source_dist;
 mod wheel;
 

crates/distribution-types/src/installed.rs

@@ -3,6 +3,7 @@ use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
 use anyhow::{anyhow, Context, Result};
+use distribution_filename::EggInfoFilename;
 use fs_err as fs;
 use tracing::warn;
 use url::Url;
@@ -117,46 +118,36 @@ impl InstalledDist {
             };
         }
 
+        // Ex) `zstandard-0.22.0-py3.12.egg-info` or `vtk-9.2.6.egg-info`
         if path.extension().is_some_and(|ext| ext == "egg-info") {
-            // Ex) `zstandard-0.22.0-py3.12.egg-info`
+            let metadata = match fs_err::metadata(path) {
-            if path.is_dir() {
+                Ok(metadata) => metadata,
-                let Some(file_stem) = path.file_stem() else {
+                Err(err) => {
+                    warn!("Invalid `.egg-info` path: {err}");
                     return Ok(None);
-                };
+                }
-                let Some(file_stem) = file_stem.to_str() else {
+            };
-                    return Ok(None);
+
-                };
+            let Some(file_stem) = path.file_stem() else {
-                let Some((name, version_python)) = file_stem.split_once('-') else {
+                return Ok(None);
-                    return Ok(None);
+            };
-                };
+            let Some(file_stem) = file_stem.to_str() else {
-                let Some((version, _)) = version_python.split_once('-') else {
+                return Ok(None);
-                    return Ok(None);
+            };
-                };
+            let file_name = EggInfoFilename::parse(file_stem)?;
-                let name = PackageName::from_str(name)?;
+
-                let version = Version::from_str(version).map_err(|err| anyhow!(err))?;
+            if metadata.is_dir() {
                 return Ok(Some(Self::EggInfoDirectory(InstalledEggInfoDirectory {
-                    name,
+                    name: file_name.name,
-                    version,
+                    version: file_name.version,
                     path: path.to_path_buf(),
                 })));
             }
 
-            // Ex) `vtk-9.2.6.egg-info`
+            if metadata.is_file() {
-            if path.is_file() {
-                let Some(file_stem) = path.file_stem() else {
-                    return Ok(None);
-                };
-                let Some(file_stem) = file_stem.to_str() else {
-                    return Ok(None);
-                };
-                let Some((name, version)) = file_stem.split_once('-') else {
-                    return Ok(None);
-                };
-                let name = PackageName::from_str(name)?;
-                let version = Version::from_str(version).map_err(|err| anyhow!(err))?;
                 return Ok(Some(Self::EggInfoFile(InstalledEggInfoFile {
-                    name,
+                    name: file_name.name,
-                    version,
+                    version: file_name.version,
                     path: path.to_path_buf(),
                 })));
             }

crates/uv/tests/pip_freeze.rs

@@ -197,7 +197,7 @@ fn freeze_with_egg_info() -> Result<()> {
 
     let site_packages = ChildPath::new(context.site_packages());
 
-    // Manually create a `.egg-info` directory.
+    // Manually create an `.egg-info` directory.
     site_packages
         .child("zstandard-0.22.0-py3.12.egg-info")
         .create_dir_all()?;
@@ -242,6 +242,96 @@ fn freeze_with_egg_info() -> Result<()> {
     Ok(())
 }
 
+/// Show an `.egg-info` package in a virtual environment. In this case, the filename omits the
+/// Python version.
+#[test]
+fn freeze_with_egg_info_no_py() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let site_packages = ChildPath::new(context.site_packages());
+
+    // Manually create an `.egg-info` directory.
+    site_packages
+        .child("zstandard-0.22.0.egg-info")
+        .create_dir_all()?;
+    site_packages
+        .child("zstandard-0.22.0.egg-info")
+        .child("top_level.txt")
+        .write_str("zstd")?;
+    site_packages
+        .child("zstandard-0.22.0.egg-info")
+        .child("SOURCES.txt")
+        .write_str("")?;
+    site_packages
+        .child("zstandard-0.22.0.egg-info")
+        .child("PKG-INFO")
+        .write_str("")?;
+    site_packages
+        .child("zstandard-0.22.0.egg-info")
+        .child("dependency_links.txt")
+        .write_str("")?;
+    site_packages
+        .child("zstandard-0.22.0.egg-info")
+        .child("entry_points.txt")
+        .write_str("")?;
+
+    // Manually create the package directory.
+    site_packages.child("zstd").create_dir_all()?;
+    site_packages
+        .child("zstd")
+        .child("__init__.py")
+        .write_str("")?;
+
+    // Run `pip freeze`.
+    uv_snapshot!(context.filters(), command(&context), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    zstandard==0.22.0
+
+    ----- stderr -----
+    "###);
+
+    Ok(())
+}
+
+/// Show a set of `.egg-info` files in a virtual environment.
+#[test]
+fn freeze_with_egg_info_file() -> Result<()> {
+    let context = TestContext::new("3.11");
+    let site_packages = ChildPath::new(context.site_packages());
+
+    // Manually create a `.egg-info` file with python version.
+    site_packages
+        .child("pycurl-7.45.1-py3.11.egg-info")
+        .write_str(indoc::indoc! {"
+            Metadata-Version: 1.1
+            Name: pycurl
+            Version: 7.45.1
+        "})?;
+
+    // Manually create another `.egg-info` file with no python version.
+    site_packages
+        .child("vtk-9.2.6.egg-info")
+        .write_str(indoc::indoc! {"
+            Metadata-Version: 1.1
+            Name: vtk
+            Version: 9.2.6
+        "})?;
+
+    // Run `pip freeze`.
+    uv_snapshot!(context.filters(), command(&context), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    pycurl==7.45.1
+    vtk==9.2.6
+
+    ----- stderr -----
+    "###);
+    Ok(())
+}
+
 #[test]
 fn freeze_with_legacy_editable() -> Result<()> {
     let context = TestContext::new("3.12");