feat(tvix/glue/store_io): have KnownPaths track fetches too r/7994

Have fetcher builtins call queue_fetch() whenever they don't need to
fetch something immediately, and teach TvixStoreIO::store_path_to_node
on how to look up (and call ingest_and persist on our Fetcher).

Change-Id: Id4bd9d639fac9e4bee20c0b1c584148740b15c2f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11501
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>

1 files changed, 14 insertions, 5 deletions

diff --git a/tvix/glue/src/builtins/fetchers.rs b/tvix/glue/src/builtins/fetchers.rs
index ec5dd969bced..0de3d5462561 100644
--- a/tvix/glue/src/builtins/fetchers.rs
+++ b/tvix/glue/src/builtins/fetchers.rs
@@ -87,11 +87,20 @@ pub(crate) mod fetcher_builtins {
             .map_err(|e| ErrorKind::TvixError(Rc::new(e)))?
         {
             Some(store_path) => {
-                let path = store_path.to_absolute_path().into();
-                // TODO: add fetch to fetcher
-                drop(fetch);
-
-                Ok(Value::Path(Box::new(path)))
+                // Move the fetch to KnownPaths, so it can be actually fetched later.
+                let sp = state
+                    .known_paths
+                    .borrow_mut()
+                    .add_fetch(fetch, &name)
+                    .expect("Tvix bug: should only fail if the store path cannot be calculated");
+
+                debug_assert_eq!(
+                    sp, store_path,
+                    "calculated store path by KnownPaths should match"
+                );
+
+                // Emit the calculated Store Path.
+                Ok(Value::Path(Box::new(store_path.to_absolute_path().into())))
             }
             None => {
                 // If we don't have enough info, do the fetch now.