Avoid reading stale .egg-info from mutable sources (#6714)

## Summary

In theory this problem already existed for `PKG-INFO`, but `egg-info`
would be more common, I think, since it's built in the source tree.

Closes https://github.com/astral-sh/uv/issues/6712.

crates/distribution-types/src/buildable.rs

@@ -56,6 +56,14 @@ impl BuildableSource<'_> {
             Self::Url(url) => url.is_editable(),
         }
     }
+
+    /// Return true if the source refers to a local source tree (i.e., a directory).
+    pub fn is_source_tree(&self) -> bool {
+        match self {
+            Self::Dist(dist) => matches!(dist, SourceDist::Directory(_)),
+            Self::Url(url) => matches!(url, SourceUrl::Directory(_)),
+        }
+    }
 }
 
 impl std::fmt::Display for BuildableSource<'_> {
@@ -94,6 +102,11 @@ impl<'a> SourceUrl<'a> {
             Self::Directory(DirectorySourceUrl { editable: true, .. })
         )
     }
+
+    /// Return true if the source refers to a local file or directory.
+    pub fn is_local(&self) -> bool {
+        matches!(self, Self::Path(_) | Self::Directory(_))
+    }
 }
 
 impl std::fmt::Display for SourceUrl<'_> {

crates/uv-distribution/src/source/mod.rs

@@ -1529,6 +1529,12 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
             Err(err) => return Err(err),
         }
 
+        // If the source distribution is a source tree, avoid reading `PKG-INFO` or `egg-info`,
+        // since they could be out-of-date.
+        if source.is_source_tree() {
+            return Ok(None);
+        }
+
         // Attempt to read static metadata from the `PKG-INFO` file.
         match read_pkg_info(source_root, subdirectory).await {
             Ok(metadata) => {

crates/uv/tests/pip_install.rs

@@ -6386,3 +6386,72 @@ fn switch_platform() -> Result<()> {
 
     Ok(())
 }
+
+/// See: <https://github.com/astral-sh/uv/pull/6714>
+#[test]
+fn stale_egg_info() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    // Create a project with dynamic metadata (version).
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "project"
+        dynamic = ["version"]
+
+        dependencies = ["iniconfig"]
+        "#
+    })?;
+
+    uv_snapshot!(context.filters(), context.pip_install()
+        .arg("-e")
+        .arg("."), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + iniconfig==2.0.0
+     + project==0.0.0 (from file://[TEMP_DIR]/)
+    "###
+    );
+
+    // Ensure that `.egg-info` exists.
+    let egg_info = context.temp_dir.child("project.egg-info");
+    egg_info.assert(predicates::path::is_dir());
+
+    // Change the metadata.
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "project"
+        dynamic = ["version"]
+
+        dependencies = ["anyio"]
+        "#
+    })?;
+
+    // Reinstall. Ensure that the metadata is updated.
+    uv_snapshot!(context.filters(), context.pip_install()
+        .arg("-e")
+        .arg("."), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    Prepared 4 packages in [TIME]
+    Uninstalled 1 package in [TIME]
+    Installed 4 packages in [TIME]
+     + anyio==4.3.0
+     + idna==3.6
+     ~ project==0.0.0 (from file://[TEMP_DIR]/)
+     + sniffio==1.3.1
+    "###
+    );
+
+    Ok(())
+}