Feature: add feature flag storage-v2 to enable RaftLogStorage and Raf…

…tStateMachine

`storage-v2`: enables `RaftLogStorage` and `RaftStateMachine` as the v2 storage
This is a temporary feature flag, and will be removed in the future, when v2 storage is stable.
This feature disables `Adapter`, which is for v1 storage to be used as v2.
V2 storage separates log store and state machine store so that log IO and state machine IO can be parallelized naturally.

guide/src/feature-flags.md

@@ -18,3 +18,9 @@ By default openraft enables no features.
    compat-07 = ["compat", "single-term-leader", "serde", "dep:or07", "compat-07-testing"]
    compat-07-testing = ["dep:tempdir", "anyhow", "dep:serde_json"]
    ```
+
+- `storage-v2`: enables `RaftLogStorage` and `RaftStateMachine` as the v2 storage
+  This is a temporary feature flag, and will be removed in the future, when v2 storage is stable.
+  This feature disables `Adapter`, which is for v1 storage to be used as v2.
+  V2 storage separates log store and state machine store so that log IO and state machine IO can be parallelized naturally. 
+

openraft/Cargo.toml

@@ -78,6 +78,11 @@ compat = []
 compat-07 = ["compat", "serde", "dep:or07", "compat-07-testing"]
 compat-07-testing = ["dep:tempfile", "anyhow", "dep:serde_json"]
 
+# Allows an application to implement a custom the v2 storage API.
+# See `openraft::storage::v2` for more details.
+# V2 API are unstable and may change in the future.
+storage-v2 = []
+
 # default = ["single-term-leader"]
 
 [package.metadata.docs.rs]

openraft/src/storage/mod.rs

@@ -1,6 +1,6 @@
 //! The Raft storage interface and data types.
 
-pub(crate) mod adapter;
+#[cfg(not(feature = "storage-v2"))] pub(crate) mod adapter;
 mod callback;
 mod helper;
 mod log_store_ext;
@@ -10,7 +10,7 @@ mod v2;
 use std::fmt::Debug;
 use std::ops::RangeBounds;
 
-pub use adapter::Adaptor;
+#[cfg(not(feature = "storage-v2"))] pub use adapter::Adaptor;
 use async_trait::async_trait;
 pub use helper::StorageHelper;
 pub use log_store_ext::RaftLogReaderExt;

openraft/src/storage/v2.rs

@@ -23,6 +23,11 @@ pub(crate) mod sealed {
     /// Seal [`RaftLogStorage`] and [`RaftStateMachine`]. This is to prevent users from implementing
     /// them before being stable.
     pub trait Sealed {}
+
+    /// Implement non-public trait [`Sealed`] for all types so that [`RaftLogStorage`] and
+    /// [`RaftStateMachine`] can be implemented by 3rd party crates.
+    #[cfg(feature = "storage-v2")]
+    impl<T> Sealed for T {}
 }
 
 #[async_trait]