Colocate Python install cache with destination directory (#6043)

## Summary

Closes https://github.com/astral-sh/uv/issues/6036.

crates/uv-python/src/downloads.rs

@@ -14,7 +14,6 @@ use tokio::io::{AsyncRead, ReadBuf};
 use tokio_util::compat::FuturesAsyncReadCompatExt;
 use tracing::{debug, instrument};
 use url::Url;
-use uv_cache::Cache;
 use uv_client::WrappedReqwestError;
 use uv_extract::hash::Hasher;
 use uv_fs::{rename_with_retry, Simplified};
@@ -408,16 +407,16 @@ impl ManagedPythonDownload {
     }
 
     /// Download and extract
-    #[instrument(skip(client, parent_path, cache, reporter), fields(download = % self.key()))]
+    #[instrument(skip(client, installation_dir, cache_dir, reporter), fields(download = % self.key()))]
     pub async fn fetch(
         &self,
         client: &uv_client::BaseClient,
-        parent_path: &Path,
-        cache: &Cache,
+        installation_dir: &Path,
+        cache_dir: &Path,
         reporter: Option<&dyn Reporter>,
     ) -> Result<DownloadResult, Error> {
         let url = self.download_url()?;
-        let path = parent_path.join(self.key().to_string());
+        let path = installation_dir.join(self.key().to_string());
 
         // If it already exists, return it
         if path.is_dir() {
@@ -438,7 +437,7 @@ impl ManagedPythonDownload {
             .map(|reporter| (reporter, reporter.on_download_start(&self.key, size)));
 
         // Download and extract into a temporary directory.
-        let temp_dir = tempfile::tempdir_in(cache.root()).map_err(Error::DownloadDirError)?;
+        let temp_dir = tempfile::tempdir_in(cache_dir).map_err(Error::DownloadDirError)?;
 
         debug!(
             "Downloading {url} to temporary location: {}",

crates/uv-python/src/installation.rs

@@ -1,11 +1,11 @@
 use std::fmt;
 use std::str::FromStr;
 
-use pep440_rs::Version;
 use tracing::{debug, info};
-use uv_client::BaseClientBuilder;
 
+use pep440_rs::Version;
 use uv_cache::Cache;
+use uv_client::BaseClientBuilder;
 
 use crate::discovery::{
     find_best_python_installation, find_python_installation, EnvironmentPreference, PythonRequest,
@@ -123,6 +123,7 @@ impl PythonInstallation {
     ) -> Result<Self, Error> {
         let installations = ManagedPythonInstallations::from_settings()?.init()?;
         let installations_dir = installations.root();
+        let cache_dir = installations.cache();
         let _lock = installations.acquire_lock()?;
 
         let download = ManagedPythonDownload::from_request(&request)?;
@@ -130,7 +131,7 @@ impl PythonInstallation {
 
         info!("Fetching requested Python...");
         let result = download
-            .fetch(&client, installations_dir, cache, reporter)
+            .fetch(&client, installations_dir, &cache_dir, reporter)
             .await?;
 
         let path = match result {

crates/uv-python/src/managed.rs

@@ -95,6 +95,11 @@ impl ManagedPythonInstallations {
         ))
     }
 
+    /// Return the location of the cache directory for managed Python installations.
+    pub fn cache(&self) -> PathBuf {
+        self.root.join(".cache")
+    }
+
     /// Initialize the Python installation directory.
     ///
     /// Ensures the directory is created.
@@ -119,6 +124,10 @@ impl ManagedPythonInstallations {
         // Create the directory, if it doesn't exist.
         fs::create_dir_all(root)?;
 
+        // Create the cache directory, if it doesn't exist.
+        let cache = self.cache();
+        fs::create_dir_all(&cache)?;
+
         // Add a .gitignore.
         match fs::OpenOptions::new()
             .write(true)
@@ -166,8 +175,10 @@ impl ManagedPythonInstallations {
                 })
             }
         };
+        let cache = self.cache();
         Ok(dirs
             .into_iter()
+            .filter(|path| *path != cache)
             .filter_map(|path| {
                 ManagedPythonInstallation::new(path)
                     .inspect_err(|err| {