backends: implement as_any() on OpStore and OpHeadsStore too

It's useful for custom commands to be able to downcast to custom
backend types.

lib/src/op_heads_store.rs

@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 
+use std::any::Any;
 use std::collections::HashSet;
 use std::fmt::Debug;
 use std::sync::Arc;
@@ -35,6 +36,8 @@ pub trait OpHeadsStoreLock {}
 
 /// Manages the set of current heads of the operation log.
 pub trait OpHeadsStore: Send + Sync + Debug {
+    fn as_any(&self) -> &dyn Any;
+
     fn name(&self) -> &str;
 
     /// Remove the old op heads and add the new one.

lib/src/op_store.rs

@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 
+use std::any::Any;
 use std::collections::{BTreeMap, HashMap, HashSet};
 use std::fmt::{Debug, Error, Formatter};
 use std::iter;
@@ -434,6 +435,8 @@ pub enum OpStoreError {
 pub type OpStoreResult<T> = Result<T, OpStoreError>;
 
 pub trait OpStore: Send + Sync + Debug {
+    fn as_any(&self) -> &dyn Any;
+
     fn name(&self) -> &str;
 
     fn root_operation_id(&self) -> &OperationId;

lib/src/simple_op_heads_store.rs

@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 
+use std::any::Any;
 use std::fmt::{Debug, Formatter};
 use std::fs;
 use std::path::{Path, PathBuf};
@@ -71,6 +72,10 @@ struct SimpleOpHeadsStoreLock {
 impl OpHeadsStoreLock for SimpleOpHeadsStoreLock {}
 
 impl OpHeadsStore for SimpleOpHeadsStore {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
     fn name(&self) -> &str {
         Self::name()
     }

lib/src/simple_op_store.rs

@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 
+use std::any::Any;
 use std::collections::{BTreeMap, HashMap, HashSet};
 use std::fmt::Debug;
 use std::io::{ErrorKind, Write};
@@ -94,6 +95,10 @@ impl SimpleOpStore {
 }
 
 impl OpStore for SimpleOpStore {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
     fn name(&self) -> &str {
         Self::name()
     }