revisionstore: move DataStore::prefetch onto RemoteDataStore

Summary:
The RemoteDataStore is expected to be implemented into the higher level types,
while we don't want low level ones to pretend to have a prefetch method.

Reviewed By: quark-zju

Differential Revision: D17437893

fbshipit-source-id: 52ec90a6edf9aa5dac852fb827275be7fd361080

edenscmnative/bindings/modules/pymanifest/src/lib.rs

@@ -18,7 +18,7 @@ use manifest::{self, DiffType, FileMetadata, FileType, FsNode, Manifest};
 use pathmatcher::{AlwaysMatcher, Matcher};
 use pypathmatcher::PythonMatcher;
 use pyrevisionstore::PythonDataStore;
-use revisionstore::DataStore;
+use revisionstore::{DataStore, RemoteDataStore};
 use types::{Key, Node, RepoPath, RepoPathBuf};
 
 struct ManifestStore<T> {
@@ -31,7 +31,7 @@ impl<T> ManifestStore<T> {
     }
 }
 
-impl<T: DataStore> manifest::TreeStore for ManifestStore<T> {
+impl<T: DataStore + RemoteDataStore> manifest::TreeStore for ManifestStore<T> {
     fn get(&self, path: &RepoPath, node: Node) -> Fallible<Bytes> {
         let key = Key::new(path.to_owned(), node);
         self.underlying.get(&key).map(|data| Bytes::from(data))

edenscmnative/bindings/modules/pyrevisionstore/src/pythondatastore.rs

@@ -8,7 +8,7 @@ use cpython::{
 };
 use failure::Fallible;
 
-use revisionstore::{DataStore, Delta, LocalStore, Metadata};
+use revisionstore::{DataStore, Delta, LocalStore, Metadata, RemoteDataStore};
 use types::Key;
 
 use crate::pyerror::pyerr_to_error;
@@ -103,7 +103,9 @@ impl DataStore for PythonDataStore {
         let py_dict = PyDict::extract(py, &py_meta).map_err(|e| pyerr_to_error(py, e))?;
         to_metadata(py, &py_dict).map_err(|e| pyerr_to_error(py, e))
     }
+}
 
+impl RemoteDataStore for PythonDataStore {
     fn prefetch(&self, keys: Vec<Key>) -> Fallible<()> {
         let gil = Python::acquire_gil();
         let py = gil.python();

lib/revisionstore/src/datastore.rs

@@ -36,9 +36,18 @@ pub trait DataStore: LocalStore {
     fn get_delta(&self, key: &Key) -> Fallible<Delta>;
     fn get_delta_chain(&self, key: &Key) -> Fallible<Vec<Delta>>;
     fn get_meta(&self, key: &Key) -> Fallible<Metadata>;
-    fn prefetch(&self, _keys: Vec<Key>) -> Fallible<()> {
-        Ok(())
-    }
+}
+
+/// The `RemoteDataStore` trait indicates that data can fetched over the network. Care must be
+/// taken to avoid serially fetching data and instead data should be fetched in bulk via the
+/// `prefetch` API.
+pub trait RemoteDataStore {
+    /// Attempt to bring the data corresponding to the passed in keys to a local store.
+    ///
+    /// When implemented on a pure remote store, like the `EdenApi`, the method will always fetch
+    /// everything that was asked. On a higher level store, such as the `ContentStore`, this will
+    /// avoid fetching data that is already present locally.
+    fn prefetch(&self, keys: Vec<Key>) -> Fallible<()>;
 }
 
 pub trait MutableDeltaStore: DataStore {
@@ -63,6 +72,14 @@ impl<T: DataStore + ?Sized, U: Deref<Target = T>> DataStore for U {
     }
 }
 
+/// Implement `RemoteDataStore` for all types that can be `Deref` into a `RemoteDataStore`. This
+/// includes all the smart pointers like `Box`, `Rc`, `Arc`.
+impl<T: RemoteDataStore + ?Sized, U: Deref<Target = T>> RemoteDataStore for U {
+    fn prefetch(&self, keys: Vec<Key>) -> Fallible<()> {
+        T::prefetch(self, keys)
+    }
+}
+
 impl<T: MutableDeltaStore + ?Sized, U: Deref<Target = T>> MutableDeltaStore for U {
     fn add(&self, delta: &Delta, metadata: &Metadata) -> Fallible<()> {
         T::add(self, delta, metadata)

lib/revisionstore/src/lib.rs

@@ -31,7 +31,7 @@ pub mod unionhistorystore;
 
 pub use crate::contentstore::ContentStore;
 pub use crate::datapack::{DataEntry, DataPack, DataPackVersion};
-pub use crate::datastore::{DataStore, Delta, Metadata, MutableDeltaStore};
+pub use crate::datastore::{DataStore, Delta, Metadata, MutableDeltaStore, RemoteDataStore};
 pub use crate::historypack::{HistoryEntry, HistoryPack, HistoryPackVersion};
 pub use crate::historystore::{Ancestors, HistoryStore, MutableHistoryStore};
 pub use crate::indexedlogdatastore::IndexedLogDataStore;