Resolve non-determistic behavior in preferences due to site-packages ordering (#2780)

Originally a regression test for #2779 but we found out that there's
some weird behavior where different `anyio` versions were preferred
based on the platform.

crates/uv-installer/src/site_packages.rs

@@ -46,7 +46,13 @@ impl<'a> SitePackages<'a> {
         for site_packages in venv.site_packages() {
             // Read the site-packages directory.
             let site_packages = match fs::read_dir(site_packages) {
-                Ok(site_packages) => site_packages,
+                Ok(site_packages) => {
+                    let mut entries = site_packages.collect::<Result<Vec<_>, std::io::Error>>()?;
+                    // TODO(zanieb): Consider filtering to just directories to reduce the size of the sort
+                    // Sort for determinism, `read_dir` is different per-platform
+                    entries.sort_by_key(fs_err::DirEntry::path);
+                    entries
+                }
                 Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                     return Ok(Self {
                         venv,
@@ -60,7 +66,6 @@ impl<'a> SitePackages<'a> {
 
             // Index all installed packages by name.
             for entry in site_packages {
-                let entry = entry?;
                 if entry.file_type()?.is_dir() {
                     let path = entry.path();
 

crates/uv-resolver/src/candidate_selector.rs

@@ -100,7 +100,9 @@ impl CandidateSelector {
                         }
                         // We do not consider installed distributions with multiple versions because
                         // during installation these must be reinstalled from the remote
-                        _ => {}
+                        _ => {
+                            debug!("Ignoring installed versions of {package_name}: multiple distributions found");
+                        }
                     }
                 }
 
@@ -130,7 +132,9 @@ impl CandidateSelector {
                 }
                 // We do not consider installed distributions with multiple versions because
                 // during installation these must be reinstalled from the remote
-                _ => {}
+                _ => {
+                    debug!("Ignoring installed versions of {package_name}: multiple distributions found");
+                }
             }
         }
 

crates/uv-resolver/src/preferences.rs

@@ -79,6 +79,9 @@ impl Preferences {
         markers: &MarkerEnvironment,
     ) -> Self {
         Self(
+            // TODO(zanieb): We should explicitly ensure that when a package name is seen multiple times
+            // that the newest or oldest version is preferred dependning on the resolution strategy;
+            // right now, the order is dependent on the given iterator.
             preferences
                 .into_iter()
                 .filter_map(|preference| {

crates/uv/tests/pip_install.rs

@@ -3517,53 +3517,38 @@ fn already_installed_local_version_of_remote_package() {
 #[test]
 #[cfg(unix)]
 fn already_installed_multiple_versions() -> Result<()> {
-    use crate::common::copy_dir_all;
+    fn prepare(context: &TestContext) -> Result<()> {
+        use crate::common::copy_dir_all;
 
-    // Install a version
-    let context1 = TestContext::new("3.12");
-    uv_snapshot!(context1.filters(), context1.install()
-        .arg("anyio==3.7.0"), @r###"
-    success: true
-    exit_code: 0
-    ----- stdout -----
+        // Install into the base environment
+        context.install().arg("anyio==3.7.0").assert().success();
 
-    ----- stderr -----
-    Resolved 3 packages in [TIME]
-    Downloaded 3 packages in [TIME]
-    Installed 3 packages in [TIME]
-     + anyio==3.7.0
-     + idna==3.6
-     + sniffio==1.3.1
-    "###
-    );
+        // Install another version into another environment
+        let context_duplicate = TestContext::new("3.12");
+        context_duplicate
+            .install()
+            .arg("anyio==4.0.0")
+            .assert()
+            .success();
 
-    // Install another version
-    let context2 = TestContext::new("3.12");
-    uv_snapshot!(context2.filters(), context2.install()
-        .arg("anyio==4.0.0"), @r###"
-    success: true
-    exit_code: 0
-    ----- stdout -----
+        // Copy the second version into the first environment
+        copy_dir_all(
+            context_duplicate
+                .site_packages()
+                .join("anyio-4.0.0.dist-info"),
+            context.site_packages().join("anyio-4.0.0.dist-info"),
+        )?;
 
-    ----- stderr -----
-    Resolved 3 packages in [TIME]
-    Downloaded 3 packages in [TIME]
-    Installed 3 packages in [TIME]
-     + anyio==4.0.0
-     + idna==3.6
-     + sniffio==1.3.1
-    "###
-    );
+        Ok(())
+    }
 
-    // Copy the second version into the first environment
-    copy_dir_all(
-        context2.site_packages().join("anyio-4.0.0.dist-info"),
-        context1.site_packages().join("anyio-4.0.0.dist-info"),
-    )?;
+    let context = TestContext::new("3.12");
+
+    prepare(&context)?;
 
     // Request the second anyio version again
     // Should remove both previous versions and reinstall the second one
-    uv_snapshot!(context1.filters(), context1.install().arg("anyio==4.0.0"), @r###"
+    uv_snapshot!(context.filters(), context.install().arg("anyio==4.0.0"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -3578,6 +3563,26 @@ fn already_installed_multiple_versions() -> Result<()> {
     "###
     );
 
+    // Reset the test context
+    prepare(&context)?;
+
+    // Request the anyio without a version specifier
+    // This is loosely a regression test for the ordering of the installation preferences
+    // from existing site-packages
+    uv_snapshot!(context.filters(), context.install().arg("anyio"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    Installed 1 package in [TIME]
+     - anyio==3.7.0
+     - anyio==4.0.0
+     + anyio==4.0.0
+    "###
+    );
+
     Ok(())
 }