Add check for slow store to be noop and conditionally replace with fa…

…st (#670)

nativelink-store/src/fast_slow_store.rs

@@ -19,6 +19,7 @@ use std::sync::Arc;
 
 use async_trait::async_trait;
 use futures::{join, FutureExt};
+use nativelink_config::stores::StoreConfig;
 use nativelink_error::{make_err, Code, Error, ResultExt};
 use nativelink_util::buf_channel::{make_buf_channel_pair, DropCloserReadHalf, DropCloserWriteHalf};
 use nativelink_util::common::DigestInfo;
@@ -44,13 +45,23 @@ impl FastSlowStore {
         fast_store: Arc<dyn Store>,
         slow_store: Arc<dyn Store>,
     ) -> Self {
+        let slow_store = if matches!(_config.slow, StoreConfig::noop) {
+            fast_store.clone()
+        } else {
+            slow_store
+        };
+
         Self { fast_store, slow_store }
     }
 
     pub fn fast_store(&self) -> &Arc<dyn Store> {
         &self.fast_store
     }
 
+    pub fn slow_store(&self) -> &Arc<dyn Store> {
+        &self.slow_store
+    }
+
     /// Ensure our fast store is populated. This should be kept as a low
     /// cost function. Since the data itself is shared and not copied it should be fairly
     /// low cost to just discard the data, but does cost a few mutex locks while

nativelink-store/tests/fast_slow_store_test.rs

@@ -18,6 +18,7 @@ use std::sync::Arc;
 use nativelink_error::Error;
 use nativelink_store::fast_slow_store::FastSlowStore;
 use nativelink_store::memory_store::MemoryStore;
+use nativelink_store::noop_store::NoopStore;
 use nativelink_util::common::DigestInfo;
 use nativelink_util::store_trait::Store;
 use rand::rngs::SmallRng;
@@ -381,4 +382,33 @@ mod fast_slow_store_tests {
         );
         Ok(())
     }
+
+    // Regression test for https://github.com/TraceMachina/nativelink/issues/665
+    #[tokio::test]
+    async fn slow_store_replaced_by_fast_store_when_noop() -> Result<(), Error> {
+        let fast_store = Arc::new(MemoryStore::new(&nativelink_config::stores::MemoryStore::default()));
+        let slow_store = Arc::new(NoopStore::new());
+        let fast_slow_store_config = nativelink_config::stores::FastSlowStore {
+            fast: nativelink_config::stores::StoreConfig::memory(nativelink_config::stores::MemoryStore::default()),
+            slow: nativelink_config::stores::StoreConfig::noop,
+        };
+        let fast_slow_store = Arc::new(FastSlowStore::new(
+            &fast_slow_store_config,
+            fast_store.clone(),
+            slow_store.clone(),
+        ));
+
+        assert_eq!(
+            Arc::as_ptr(fast_slow_store.fast_store()),
+            Arc::as_ptr(&fast_store),
+            "Fast store should be the same as the fast_slow_store's fast store"
+        );
+        assert_eq!(
+            Arc::as_ptr(fast_slow_store.slow_store()),
+            Arc::as_ptr(&fast_store),
+            "Slow store should be replaced by fast store when configured as noop"
+        );
+
+        Ok(())
+    }
 }