refactor: put PackageCache into an enum in preparation for a multi-layered package cache

crates/rattler-bin/src/commands/create.rs

@@ -145,7 +145,7 @@ pub async fn create(opt: Opt) -> anyhow::Result<()> {
     // Get the package names from the matchspecs so we can only load the package records that we need.
     let gateway = Gateway::builder()
         .with_cache_dir(cache_dir.join(rattler_cache::REPODATA_CACHE_DIR))
-        .with_package_cache(PackageCache::new(
+        .with_package_cache(PackageCache::new_singleton(
             cache_dir.join(rattler_cache::PACKAGE_CACHE_DIR),
         ))
         .with_client(download_client.clone())

crates/rattler/src/install/clobber_registry.rs

@@ -476,7 +476,7 @@ mod tests {
         let target_prefix = tempfile::tempdir().unwrap();
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         execute_transaction(
             transaction,
@@ -597,7 +597,7 @@ mod tests {
             let target_prefix = tempfile::tempdir().unwrap();
 
             let packages_dir = tempfile::tempdir().unwrap();
-            let cache = PackageCache::new(packages_dir.path());
+            let cache = PackageCache::new_singleton(packages_dir.path());
 
             execute_transaction(
                 transaction,
@@ -679,7 +679,7 @@ mod tests {
             let target_prefix = tempfile::tempdir().unwrap();
 
             let packages_dir = tempfile::tempdir().unwrap();
-            let cache = PackageCache::new(packages_dir.path());
+            let cache = PackageCache::new_singleton(packages_dir.path());
 
             execute_transaction(
                 transaction,
@@ -782,7 +782,7 @@ mod tests {
         let target_prefix = tempfile::tempdir().unwrap();
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         execute_transaction(
             transaction,
@@ -883,7 +883,7 @@ mod tests {
         let target_prefix = tempfile::tempdir().unwrap();
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         execute_transaction(
             transaction,
@@ -1013,7 +1013,7 @@ mod tests {
         let target_prefix = tempfile::tempdir().unwrap();
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         let install_options = InstallOptions {
             python_info: Some(python_info.clone()),
@@ -1062,7 +1062,7 @@ mod tests {
         let target_prefix = tempfile::tempdir().unwrap();
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         execute_transaction(
             transaction,
@@ -1129,7 +1129,7 @@ mod tests {
         let target_prefix = tempfile::tempdir().unwrap();
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         execute_transaction(
             transaction,

crates/rattler/src/install/installer/mod.rs

@@ -274,7 +274,7 @@ impl Installer {
             .downloader
             .unwrap_or_else(|| reqwest_middleware::ClientWithMiddleware::from(Client::default()));
         let package_cache = self.package_cache.unwrap_or_else(|| {
-            PackageCache::new(
+            PackageCache::new_singleton(
                 default_cache_dir()
                     .expect("failed to determine default cache directory")
                     .join(rattler_cache::PACKAGE_CACHE_DIR),

crates/rattler/src/install/link_script.rs

@@ -264,7 +264,7 @@ mod tests {
         };
 
         let packages_dir = tempfile::tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
         let driver = InstallDriver::builder().execute_link_scripts(true).finish();
 
         execute_transaction(

crates/rattler/src/install/mod.rs

@@ -777,7 +777,8 @@ mod test {
         // Open a package cache in the systems temporary directory with a specific name.
         // This allows us to reuse a package cache across multiple invocations
         // of this test. Useful if you're debugging.
-        let package_cache = PackageCache::new(temp_dir().join("rattler").join(cache_name));
+        let package_cache =
+            PackageCache::new_singleton(temp_dir().join("rattler").join(cache_name));
 
         // Create an HTTP client we can use to download packages
         let client = reqwest_middleware::ClientWithMiddleware::from(reqwest::Client::new());

crates/rattler_cache/src/package_cache.rs

@@ -47,8 +47,11 @@ pub trait CacheReporter: Send + Sync {
 /// cache is stale a user defined function is called to populate the cache. This
 /// separates the corners between caching and fetching of the content.
 #[derive(Clone)]
-pub struct PackageCache {
-    inner: Arc<Mutex<PackageCacheInner>>,
+pub enum PackageCache {
+    /// A package cache which reads/writes from only one directory.
+    SingletonPackageCache {
+        inner: Arc<Mutex<PackageCacheInner>>,
+    },
 }
 
 /// Provides a unique identifier for packages in the cache.
@@ -112,7 +115,7 @@ impl Display for CacheKey {
 }
 
 #[derive(Default)]
-struct PackageCacheInner {
+pub struct PackageCacheInner {
     path: PathBuf,
     packages: FxHashMap<CacheKey, Arc<Mutex<Package>>>,
 }
@@ -133,16 +136,21 @@ pub enum PackageCacheError {
 }
 
 impl PackageCache {
-    /// Constructs a new [`PackageCache`] located at the specified path.
-    pub fn new(path: impl Into<PathBuf>) -> Self {
-        Self {
+    pub fn new_singleton(path: impl Into<PathBuf>) -> Self {
+        Self::SingletonPackageCache {
             inner: Arc::new(Mutex::new(PackageCacheInner {
                 path: path.into(),
                 packages: FxHashMap::default(),
             })),
         }
     }
 
+    fn get_inner(&self) -> Arc<Mutex<PackageCacheInner>> {
+        match self {
+            Self::SingletonPackageCache { inner } => inner.clone(),
+        }
+    }
+
     /// Returns the directory that contains the specified package.
     ///
     /// If the package was previously successfully fetched and stored in the
@@ -168,7 +176,8 @@ impl PackageCache {
 
         // Get the package entry
         let (package, pkg_cache_dir) = {
-            let mut inner = self.inner.lock();
+            let _inner = self.get_inner();
+            let mut inner = _inner.lock();
             let destination = inner.path.join(cache_key.to_string());
             let package = inner.packages.entry(cache_key).or_default().clone();
             (package, destination)
@@ -455,7 +464,7 @@ mod test {
         };
 
         let packages_dir = tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         // Get the package to the cache
         let package_dir = cache
@@ -590,7 +599,7 @@ mod test {
         tokio::spawn(axum::serve(listener, service).into_future());
 
         let packages_dir = tempdir().unwrap();
-        let cache = PackageCache::new(packages_dir.path());
+        let cache = PackageCache::new_singleton(packages_dir.path());
 
         let server_url = Url::parse(&format!("http://localhost:{}", addr.port())).unwrap();
 

crates/rattler_repodata_gateway/src/gateway/builder.rs

@@ -99,7 +99,7 @@ impl GatewayBuilder {
                 .join("rattler/cache")
         });
 
-        let package_cache = self.package_cache.unwrap_or(PackageCache::new(
+        let package_cache = self.package_cache.unwrap_or(PackageCache::new_singleton(
             cache.join(rattler_cache::PACKAGE_CACHE_DIR),
         ));
 

crates/rattler_repodata_gateway/src/gateway/direct_url_query.rs

@@ -121,7 +121,7 @@ mod test {
             "https://conda.anaconda.org/conda-forge/noarch/boltons-24.0.0-pyhd8ed1ab_0.conda",
         )
         .unwrap();
-        let package_cache = PackageCache::new(PathBuf::from("/tmp"));
+        let package_cache = PackageCache::new_singleton(PathBuf::from("/tmp"));
         let client = reqwest_middleware::ClientWithMiddleware::from(reqwest::Client::new());
         let query = DirectUrlQuery::new(url.clone(), package_cache, client, None);
 
@@ -163,7 +163,7 @@ mod test {
         .unwrap();
 
         let url = Url::from_file_path(package_path).unwrap();
-        let package_cache = PackageCache::new(temp_dir());
+        let package_cache = PackageCache::new_singleton(temp_dir());
         let client = reqwest_middleware::ClientWithMiddleware::from(reqwest::Client::new());
         let query = DirectUrlQuery::new(url.clone(), package_cache, client, None);
 

crates/rattler_repodata_gateway/src/gateway/mod.rs

@@ -433,7 +433,7 @@ mod test {
     #[tokio::test]
     async fn test_direct_url_spec_from_gateway() {
         let gateway = Gateway::builder()
-            .with_package_cache(PackageCache::new(
+            .with_package_cache(PackageCache::new_singleton(
                 default_cache_dir()
                     .unwrap()
                     .join(rattler_cache::PACKAGE_CACHE_DIR),
@@ -494,7 +494,7 @@ mod test {
     #[tokio::test]
     async fn test_select_forced_url_instead_of_deps() {
         let gateway = Gateway::builder()
-            .with_package_cache(PackageCache::new(
+            .with_package_cache(PackageCache::new_singleton(
                 default_cache_dir()
                     .unwrap()
                     .join(rattler_cache::PACKAGE_CACHE_DIR),

py-rattler/src/installer.rs

@@ -59,7 +59,7 @@ pub fn py_install<'a>(
         }
 
         if let Some(cache_dir) = cache_dir {
-            installer.set_package_cache(PackageCache::new(cache_dir));
+            installer.set_package_cache(PackageCache::new_singleton(cache_dir));
         }
 
         if let Some(installed_packages) = installed_packages {