refactor(downloader): introduce top-level downloader module

Move VCS downloaders and DownloadManager out of vcs/repository into a
new top-level downloader module mirroring Composer\Downloader, and add
stub types for the remaining Composer downloader hierarchy (file,
archive variants, path, perforce, fossil, exceptions, interfaces) so
future ports have a home.

2 files changed, 9 insertions, 152 deletions

diff --git a/crates/mozart-core/src/repository/download_manager.rs b/crates/mozart-core/src/repository/download_manager.rs
deleted file mode 100644
index d422899..0000000
--- a/crates/mozart-core/src/repository/download_manager.rs
+++ /dev/null
@@ -1,143 +0,0 @@
-//! `DownloadManager` — pick the right [`VcsDownloader`] for a given
-//! [`LocalPackage`]. Mirrors `Composer\Downloader\DownloadManager`.
-
-use std::path::PathBuf;
-
-use crate::composer::{InstallationSource, LocalPackage};
-use crate::vcs::downloader::VcsDownloader;
-use crate::vcs::downloader::git::GitDownloader;
-use crate::vcs::downloader::hg::HgDownloader;
-use crate::vcs::downloader::svn::SvnDownloader;
-use crate::vcs::process::ProcessExecutor;
-use crate::vcs::util::git::GitUtil;
-use crate::vcs::util::hg::HgUtil;
-use crate::vcs::util::svn::SvnUtil;
-
-/// Selects a `VcsDownloader` for a package based on its installation source
-/// and source type. Mirrors `DownloadManager::getDownloaderForPackage`:
-///
-/// - `metapackage` → `None`.
-/// - `installation-source: dist` → `None` (Composer would return a
-///   `FileDownloader`-family object that does not implement
-///   `ChangeReportInterface` / `DvcsDownloaderInterface`, so the status
-///   command's `instanceof` checks all become no-ops; returning `None`
-///   directly is the equivalent in our trait-object world).
-/// - `installation-source: source` → the matching VCS downloader by
-///   `source.type` (`git` / `hg` / `svn`).
-pub struct DownloadManager {
-    git_cache_dir: PathBuf,
-}
-
-impl DownloadManager {
-    /// `git_cache_dir`: where `GitUtil` should keep mirror clones (e.g.
-    /// `<vendor>/.cache/git`).
-    pub fn new(git_cache_dir: PathBuf) -> Self {
-        Self { git_cache_dir }
-    }
-
-    pub fn get_downloader_for_package(
-        &self,
-        package: &LocalPackage,
-    ) -> Option<Box<dyn VcsDownloader>> {
-        if package.package_type() == Some("metapackage") {
-            return None;
-        }
-        match package.installation_source()? {
-            InstallationSource::Dist => None,
-            InstallationSource::Source => {
-                let kind = package.source()?.kind.as_str();
-                match kind {
-                    "git" => {
-                        let git_util =
-                            GitUtil::new(ProcessExecutor::new(), self.git_cache_dir.clone());
-                        Some(Box::new(GitDownloader::new(git_util)))
-                    }
-                    "hg" => {
-                        let hg_util = HgUtil::new(ProcessExecutor::new());
-                        Some(Box::new(HgDownloader::new(hg_util)))
-                    }
-                    "svn" => {
-                        let svn_util = SvnUtil::new(ProcessExecutor::new());
-                        Some(Box::new(SvnDownloader::new(svn_util)))
-                    }
-                    _ => None,
-                }
-            }
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::composer::PackageReference;
-    use serde_json::Value;
-
-    fn pkg(
-        installation_source: Option<InstallationSource>,
-        source_kind: Option<&str>,
-    ) -> LocalPackage {
-        let source = source_kind.map(|kind| PackageReference {
-            kind: kind.to_string(),
-            url: "https://example/repo".into(),
-            reference: Some("abc123".into()),
-            shasum: None,
-        });
-        LocalPackage::new(
-            "vendor/pkg".into(),
-            "1.0.0".into(),
-            None,
-            Some("library".into()),
-            installation_source,
-            source,
-            None,
-            Value::Null,
-        )
-    }
-
-    #[test]
-    fn metapackage_returns_none() {
-        let dm = DownloadManager::new(PathBuf::from("/tmp/mz-test-cache"));
-        let mut p = pkg(Some(InstallationSource::Source), Some("git"));
-        // override type
-        p = LocalPackage::new(
-            "vendor/pkg".into(),
-            "1.0.0".into(),
-            None,
-            Some("metapackage".into()),
-            p.installation_source(),
-            p.source().cloned(),
-            None,
-            Value::Null,
-        );
-        assert!(dm.get_downloader_for_package(&p).is_none());
-    }
-
-    #[test]
-    fn dist_install_returns_none() {
-        let dm = DownloadManager::new(PathBuf::from("/tmp/mz-test-cache"));
-        let p = pkg(Some(InstallationSource::Dist), Some("git"));
-        assert!(dm.get_downloader_for_package(&p).is_none());
-    }
-
-    #[test]
-    fn source_install_with_git_returns_some() {
-        let dm = DownloadManager::new(PathBuf::from("/tmp/mz-test-cache"));
-        let p = pkg(Some(InstallationSource::Source), Some("git"));
-        assert!(dm.get_downloader_for_package(&p).is_some());
-    }
-
-    #[test]
-    fn unknown_source_kind_returns_none() {
-        let dm = DownloadManager::new(PathBuf::from("/tmp/mz-test-cache"));
-        let p = pkg(Some(InstallationSource::Source), Some("perforce"));
-        assert!(dm.get_downloader_for_package(&p).is_none());
-    }
-
-    #[test]
-    fn missing_installation_source_returns_none() {
-        let dm = DownloadManager::new(PathBuf::from("/tmp/mz-test-cache"));
-        let p = pkg(None, Some("git"));
-        assert!(dm.get_downloader_for_package(&p).is_none());
-    }
-}
diff --git a/crates/mozart-core/src/repository/installer_executor/filesystem.rs b/crates/mozart-core/src/repository/installer_executor/filesystem.rs
index 3f982e3..2b34e02 100644
--- a/crates/mozart-core/src/repository/installer_executor/filesystem.rs
+++ b/crates/mozart-core/src/repository/installer_executor/filesystem.rs
@@ -5,9 +5,10 @@
 //! [`crate::vcs`], and removes vendor directories. Test code substitutes a
 //! recording-only executor instead (added in a later step).
 
-use super::super::cache::Cache;
-use super::super::downloader;
-use super::{ExecuteContext, InstallerExecutor, PackageOperation};
+use crate::downloader::{GitDownloader, HgDownloader, SvnDownloader};
+use crate::repository::cache::Cache;
+use crate::repository::downloader;
+use crate::repository::installer_executor::{ExecuteContext, InstallerExecutor, PackageOperation};
 use std::path::Path;
 
 pub struct FilesystemExecutor {
@@ -135,6 +136,8 @@ fn install_from_source(
     vendor_dir: &Path,
     package_name: &str,
 ) -> anyhow::Result<()> {
+    use crate::downloader::VcsDownloader as _;
+
     let target = vendor_dir.join(package_name);
     if target.exists() {
         std::fs::remove_dir_all(&target)?;
@@ -145,23 +148,20 @@ fn install_from_source(
             let process = crate::vcs::process::ProcessExecutor::new();
             let git_util =
                 crate::vcs::util::git::GitUtil::new(process, vendor_dir.join(".cache").join("git"));
-            let downloader = crate::vcs::downloader::git::GitDownloader::new(git_util);
-            use crate::vcs::downloader::VcsDownloader as _;
+            let downloader = GitDownloader::new(git_util);
             downloader.download(url, reference, &target)?;
             downloader.install(url, reference, &target)?;
         }
         "svn" => {
             let process = crate::vcs::process::ProcessExecutor::new();
             let svn_util = crate::vcs::util::svn::SvnUtil::new(process);
-            let downloader = crate::vcs::downloader::svn::SvnDownloader::new(svn_util);
-            use crate::vcs::downloader::VcsDownloader as _;
+            let downloader = SvnDownloader::new(svn_util);
             downloader.install(url, reference, &target)?;
         }
         "hg" => {
             let process = crate::vcs::process::ProcessExecutor::new();
             let hg_util = crate::vcs::util::hg::HgUtil::new(process);
-            let downloader = crate::vcs::downloader::hg::HgDownloader::new(hg_util);
-            use crate::vcs::downloader::VcsDownloader as _;
+            let downloader = HgDownloader::new(hg_util);
             downloader.install(url, reference, &target)?;
         }
         _ => {