backingstore: add TreeContentStore to impl TreeStore

Summary: `manifest::Tree` wants to have a store that implements `TreeStore`. However at current we don't want to introduce dependency between `manifest` and `contentstore`. So we create this wrapper struct to provide the trait implementation. This will allow us to use `manifest` to parse manifest data we get from hg store.

Reviewed By: chadaustin, xavierd

Differential Revision: D18365354

fbshipit-source-id: 3687032c7f51570ef51ccc4004efc87f64ef2188

eden/scm/lib/backingstore/Cargo.toml

@@ -5,8 +5,9 @@ authors = ["Facebook Source Control Team <sourcecontrol-dev@fb.com>"]
 edition = "2018"
 
 [dependencies]
-revisionstore = { path = "../revisionstore" }
 configparser = { path = "../configparser" }
+manifest = { path = "../manifest" }
+revisionstore = { path = "../revisionstore" }
 types = { path = "../types" }
 bytes = "0.4.12"
 failure = "0.1.6"

eden/scm/lib/backingstore/src/lib.rs

@@ -15,5 +15,6 @@
 
 mod backingstore;
 mod raw;
+mod treecontentstore;
 
 pub use crate::backingstore::BackingStore;

eden/scm/lib/backingstore/src/treecontentstore.rs

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This software may be used and distributed according to the terms of the
+ * GNU General Public License version 2.
+ */
+
+use bytes::Bytes;
+use failure::{format_err, Fallible};
+use manifest::TreeStore;
+use revisionstore::{ContentStore, DataStore};
+use types::{HgId, Key, RepoPath};
+
+pub(crate) struct TreeContentStore {
+    inner: ContentStore,
+}
+
+impl TreeContentStore {
+    pub fn new(inner: ContentStore) -> Self {
+        TreeContentStore { inner }
+    }
+}
+
+impl TreeStore for TreeContentStore {
+    fn get(&self, path: &RepoPath, hgid: HgId) -> Fallible<Bytes> {
+        let key = Key::new(path.to_owned(), hgid);
+
+        self.inner.get(&key).and_then(|opt| {
+            opt.ok_or_else(|| format_err!("hgid: {:?} path: {:?} is not found.", path, hgid))
+                .map(Into::into)
+        })
+    }
+
+    fn insert(&self, _path: &RepoPath, _hgid: HgId, _data: Bytes) -> Fallible<()> {
+        Err(format_err!("insert is not implemented."))
+    }
+}