feat: add ChainState type (#1249)

crates/storage/provider/src/providers/mod.rs

@@ -10,6 +10,7 @@ use std::sync::Arc;
 
 mod state;
 pub use state::{
+    chain::ChainState,
     historical::{HistoricalStateProvider, HistoricalStateProviderRef},
     latest::{LatestStateProvider, LatestStateProviderRef},
 };

crates/storage/provider/src/providers/state/chain.rs

@@ -0,0 +1,18 @@
+use crate::StateProvider;
+use std::marker::PhantomData;
+
+/// A type that can access the state at a specific access point (block number or tag)
+///
+/// Depending on the desired access point, the state must be accessed differently. For example, the
+/// "Latest" state is stored in a different location than previous blocks. And the "Pending" state
+/// is accessed differently than the "Latest" state.
+///
+/// This unifies [StateProvider] access when the caller does not know or care where the state is
+/// being accessed from, e.g. in RPC where the requested access point may be
+/// `Pending|Latest|Number|Hash`.
+///
+/// Note: The lifetime of this type is limited by the type that created it.
+pub struct ChainState<'a> {
+    _inner: Box<dyn StateProvider>,
+    _phantom: PhantomData<&'a ()>,
+}

crates/storage/provider/src/providers/state/mod.rs

@@ -1,3 +1,4 @@
 //! [StateProvider](crate::StateProvider) implementations
+pub(crate) mod chain;
 pub(crate) mod historical;
 pub(crate) mod latest;

crates/storage/provider/src/traits/state.rs

@@ -7,7 +7,7 @@ use reth_primitives::{
 };
 
 /// An abstraction for a type that provides state data.
-#[auto_impl(&)]
+#[auto_impl(&, Box)]
 pub trait StateProvider: BlockHashProvider + AccountProvider + Send + Sync {
     /// Get storage.
     fn storage(&self, account: Address, storage_key: StorageKey) -> Result<Option<StorageValue>>;