use a distinct error for out-of-sync replica

taskchampion/src/errors.rs

@@ -4,6 +4,12 @@ use thiserror::Error;
 #[non_exhaustive]
 /// Errors returned from taskchampion operations
 pub enum Error {
+    /// A task-database-related error
     #[error("Task Database Error: {0}")]
     Database(String),
+    /// An error specifically indicating that the local replica cannot
+    /// be synchronized with the sever, due to being out of date or some
+    /// other irrecoverable error.
+    #[error("Local replica is out of sync with the server")]
+    OutOfSync,
 }

taskchampion/src/replica.rs

@@ -140,7 +140,7 @@ impl Replica {
     ) -> anyhow::Result<()> {
         self.taskdb
             .sync(server, avoid_snapshots)
-            .context("Failed to synchronize")?;
+            .context("Failed to synchronize with server")?;
         self.rebuild_working_set(false)
             .context("Failed to rebuild working set after sync")?;
         Ok(())

taskchampion/src/taskdb/sync.rs

@@ -1,6 +1,7 @@
 use super::{ops, snapshot};
 use crate::server::{AddVersionResult, GetVersionResult, Server, SnapshotUrgency};
 use crate::storage::{Operation, StorageTxn};
+use crate::Error;
 use log::{info, trace, warn};
 use serde::{Deserialize, Serialize};
 use std::str;
@@ -97,7 +98,7 @@ pub(super) fn sync(
                 );
                 if let Some(requested) = requested_parent_version_id {
                     if parent_version_id == requested {
-                        anyhow::bail!("Server's task history has diverged from this replica");
+                        return Err(Error::OutOfSync.into());
                     }
                 }
                 requested_parent_version_id = Some(parent_version_id);