refactor(downloader): take &self across the downloader hierarchy

Concurrent package operations call into the same downloader instances
through Rc<RefCell<dyn DownloaderInterface>>; with &mut self methods
every call holds a RefMut across its awaits, which panics with
'already mutably borrowed' the moment two operations overlap. This is
groundwork for fanning out InstallationManager's download/install
loops (same rework HttpDownloader/CurlDownloader already got).

- DownloaderInterface/ChangeReportInterface/ArchiveDownloader/
  VcsDownloader methods now take &self; as_change_report_interface
  returns &dyn instead of &mut dyn.
- Implementors move their genuinely mutable state behind cells:
  FileDownloader.additional_cleanup_paths, the archive downloaders'
  cleanup_executed, ZipDownloader.zip_archive_object,
  VcsDownloaderBase.has_cleaned_changes, GitDownloader's stash/discard/
  cache maps and GitUtil, SvnDownloader.cache_credentials,
  PerforceDownloader.perforce. FileDownloader.io gains a RefCell layer
  so get_local_changes can keep PHP's NullIO swap under &self.
- ProcessExecutor::execute_async now returns a future that captures
  everything up front instead of borrowing the executor, and call
  sites build the future before awaiting, so no borrow on the shared
  executor is held while a subprocess runs.
- Filesystem::remove_directory_async becomes remove_directory_async_via
  taking the Rc handle: the Filesystem is only borrowed for the sync
  head/tail, never across the rm subprocess await (sync borrow_mut
  users like rename/ensure_directory_exists would otherwise collide).
- DownloadManager async call sites hold shared borrows only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

1 files changed, 10 insertions, 12 deletions

diff --git a/crates/shirabe/src/downloader/downloader_interface.rs b/crates/shirabe/src/downloader/downloader_interface.rs
index f63ac4e8..873438e2 100644
--- a/crates/shirabe/src/downloader/downloader_interface.rs
+++ b/crates/shirabe/src/downloader/downloader_interface.rs
@@ -8,7 +8,7 @@ pub trait DownloaderInterface: std::fmt::Debug {
     fn get_installation_source(&self) -> String;
 
     async fn download(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         prev_package: Option<PackageInterfaceHandle>,
@@ -17,7 +17,7 @@ pub trait DownloaderInterface: std::fmt::Debug {
 
     /// Convenience for the PHP default `$output = true` overload.
     async fn download3(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         prev_package: Option<PackageInterfaceHandle>,
@@ -26,7 +26,7 @@ pub trait DownloaderInterface: std::fmt::Debug {
     }
 
     async fn prepare(
-        &mut self,
+        &self,
         r#type: &str,
         package: PackageInterfaceHandle,
         path: &str,
@@ -34,7 +34,7 @@ pub trait DownloaderInterface: std::fmt::Debug {
     ) -> anyhow::Result<Option<PhpMixed>>;
 
     async fn install(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         output: bool,
@@ -42,7 +42,7 @@ pub trait DownloaderInterface: std::fmt::Debug {
 
     /// Convenience for the PHP default `$output = true` overload.
     async fn install2(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
     ) -> anyhow::Result<Option<PhpMixed>> {
@@ -50,14 +50,14 @@ pub trait DownloaderInterface: std::fmt::Debug {
     }
 
     async fn update(
-        &mut self,
+        &self,
         initial: PackageInterfaceHandle,
         target: PackageInterfaceHandle,
         path: &str,
     ) -> anyhow::Result<Option<PhpMixed>>;
 
     async fn remove(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
         output: bool,
@@ -65,7 +65,7 @@ pub trait DownloaderInterface: std::fmt::Debug {
 
     /// Convenience for the PHP default `$output = true` overload.
     async fn remove2(
-        &mut self,
+        &self,
         package: PackageInterfaceHandle,
         path: &str,
     ) -> anyhow::Result<Option<PhpMixed>> {
@@ -73,16 +73,14 @@ pub trait DownloaderInterface: std::fmt::Debug {
     }
 
     async fn cleanup(
-        &mut self,
+        &self,
         r#type: &str,
         package: PackageInterfaceHandle,
         path: &str,
         prev_package: Option<PackageInterfaceHandle>,
     ) -> anyhow::Result<Option<PhpMixed>>;
 
-    fn as_change_report_interface(
-        &mut self,
-    ) -> Option<&mut dyn crate::downloader::ChangeReportInterface> {
+    fn as_change_report_interface(&self) -> Option<&dyn crate::downloader::ChangeReportInterface> {
         None
     }