feat(tvix/castore): add composition module

Change-Id: I0868f3278db85ae5fe030089ee9033837bc08748
Signed-off-by: Yureka <tvl@yuka.dev>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11853
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/castore/src/directoryservice/memory.rs

@@ -8,6 +8,7 @@ use tracing::{instrument, warn};
 
 use super::utils::traverse_directory;
 use super::{DirectoryPutter, DirectoryService, SimplePutter};
+use crate::composition::{CompositionContext, ServiceBuilder};
 
 #[derive(Clone, Default)]
 pub struct MemoryDirectoryService {
@@ -85,3 +86,19 @@ impl DirectoryService for MemoryDirectoryService {
         Box::new(SimplePutter::new(self.clone()))
     }
 }
+
+#[derive(serde::Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct MemoryDirectoryServiceConfig {}
+
+#[async_trait]
+impl ServiceBuilder for MemoryDirectoryServiceConfig {
+    type Output = dyn DirectoryService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        _context: &CompositionContext<dyn DirectoryService>,
+    ) -> Result<Arc<dyn DirectoryService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        Ok(Arc::new(MemoryDirectoryService::default()))
+    }
+}