docs(tvix/composition): add comment about stack r/8391

Change-Id: I3888b5034c53728e2f9cfe24213f8854eb38bfe1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12005
Autosubmit: yuka <yuka@yuka.dev>
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

1 files changed, 3 insertions, 0 deletions

diff --git a/tvix/castore/src/composition.rs b/tvix/castore/src/composition.rs
index 53e2fe1594fb..53673cf46e45 100644
--- a/tvix/castore/src/composition.rs
+++ b/tvix/castore/src/composition.rs
@@ -274,6 +274,9 @@ pub fn add_default_services(reg: &mut Registry) {
 }
 
 pub struct CompositionContext<'a> {
+    // The stack used to detect recursive instantiations and prevent deadlocks
+    // The TypeId of the trait object is included to distinguish e.g. the
+    // BlobService "default" and the DirectoryService "default".
     stack: Vec<(TypeId, String)>,
     composition: Option<&'a Composition>,
 }