refactor(store)!: reset to defaults before merging the on-disk state in reload (#3599)

* refactor(store)!: reset to defaults before merging the on-disk state in reload

`Store::reload` / `reload()` previously merged the on-disk state into the
current in-memory store. It now resets the store to its defaults first,
so in-memory keys that are neither in the defaults nor on disk are
dropped. `reload_ignore_defaults` / `reload({ ignoreDefaults: true })`
is unchanged.

* test(store): cover reload resetting to the defaults before merging the on-disk state

---------

Co-authored-by: Lucas Nogueira <lucas@crabnebula.dev>

.changes/store-reload-defaults.md

@@ -0,0 +1,6 @@
+---
+"store": major
+"store-js": major
+---
+
+**Breaking:** `Store::reload` (and `reload()` in JavaScript) now resets the store to its defaults before merging the on-disk state into it, so in-memory keys that are neither in the defaults nor on disk are dropped. Previously the on-disk state was merged into the current in-memory store. Use `reload_ignore_defaults` / `reload({ ignoreDefaults: true })` to fully match the on-disk state.

plugins/store/Cargo.toml

@@ -35,3 +35,6 @@ tracing = { workspace = true }
 thiserror = { workspace = true }
 dunce = { workspace = true }
 tokio = { version = "1", features = ["sync", "time", "macros"] }
+
+[dev-dependencies]
+tauri = { workspace = true, features = ["test"] }

plugins/store/guest-js/index.ts

@@ -405,9 +405,9 @@ interface IStore {
    * This method is useful if the on-disk state was edited by the user and you want to synchronize the changes.
    *
    * Note:
-   *   - This method loads the data and merges it with the current store,
-   *     this behavior will be changed to resetting to default first and then merging with the on-disk state in v3,
-   *     to fully match the store with the on-disk state, set {@linkcode ReloadOptions | ignoreDefaults} to `true`
+   *   - This method resets the store to its defaults and then merges the on-disk state into it,
+   *     so keys that are neither in the defaults nor on disk are dropped.
+   *     To fully match the store with the on-disk state (ignoring defaults), set {@linkcode ReloadOptions | ignoreDefaults} to `true`
    *   - This method does not emit change events.
    *
    * @returns

plugins/store/src/store.rs

@@ -300,12 +300,13 @@ impl<R: Runtime> StoreInner<R> {
 
     /// Update the store from the on-disk state
     ///
-    /// Note: This method loads the data and merges it with the current store
+    /// Note: This method resets the store to its defaults and then merges the on-disk state into it
     pub fn load(&mut self) -> crate::Result<()> {
         let bytes = fs::read(&self.path)?;
+        let entries = (self.deserialize_fn)(&bytes).map_err(crate::Error::Deserialize)?;
 
-        self.cache
-            .extend((self.deserialize_fn)(&bytes).map_err(crate::Error::Deserialize)?);
+        self.cache = self.defaults.clone().unwrap_or_default();
+        self.cache.extend(entries);
 
         Ok(())
     }
@@ -525,9 +526,9 @@ impl<R: Runtime> Store<R> {
     /// Update the store from the on-disk state
     ///
     /// Note:
-    ///   - This method loads the data and merges it with the current store,
-    ///     this behavior will be changed to resetting to default first and then merging with the on-disk state in v3,
-    ///     to fully match the store with the on-disk state,
+    ///   - This method resets the store to its defaults and then merges the on-disk state into it,
+    ///     so keys that are neither in the defaults nor on disk are dropped.
+    ///     To fully match the store with the on-disk state (ignoring defaults),
     ///     use [`reload_ignore_defaults`](Self::reload_ignore_defaults) instead
     ///   - This method does not emit change events
     pub fn reload(&self) -> crate::Result<()> {
@@ -613,3 +614,74 @@ impl<R: Runtime> Drop for Store<R> {
         self.apply_pending_auto_save();
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+    use tauri::{
+        test::{mock_app, MockRuntime},
+        App,
+    };
+
+    fn temp_store_path(name: &str) -> PathBuf {
+        let dir =
+            std::env::temp_dir().join(format!("tauri-plugin-store-{}-{name}", std::process::id()));
+        fs::create_dir_all(&dir).unwrap();
+        dir.join("store.json")
+    }
+
+    fn store(app: &App<MockRuntime>, path: PathBuf) -> StoreInner<MockRuntime> {
+        let mut defaults = HashMap::new();
+        defaults.insert("default-key".to_string(), json!("default"));
+        defaults.insert("shared-key".to_string(), json!("default"));
+        StoreInner::new(
+            app.handle().clone(),
+            path,
+            Some(defaults),
+            crate::default_serialize,
+            crate::default_deserialize,
+        )
+    }
+
+    #[test]
+    fn load_resets_to_defaults_before_merging_the_on_disk_state() {
+        let app = mock_app();
+        let path = temp_store_path("load");
+        let mut store = store(&app, path.clone());
+        fs::write(&path, r#"{ "disk-key": "disk", "shared-key": "disk" }"#).unwrap();
+        // neither in the defaults nor on disk, so it must be dropped
+        store
+            .cache
+            .insert("memory-key".to_string(), json!("memory"));
+
+        store.load().unwrap();
+
+        assert_eq!(store.get("default-key"), Some(&json!("default")));
+        assert_eq!(store.get("disk-key"), Some(&json!("disk")));
+        // the on-disk state takes precedence over the defaults
+        assert_eq!(store.get("shared-key"), Some(&json!("disk")));
+        assert_eq!(store.get("memory-key"), None);
+
+        let _ = fs::remove_dir_all(path.parent().unwrap());
+    }
+
+    #[test]
+    fn load_ignore_defaults_matches_the_on_disk_state() {
+        let app = mock_app();
+        let path = temp_store_path("load-ignore-defaults");
+        let mut store = store(&app, path.clone());
+        fs::write(&path, r#"{ "disk-key": "disk" }"#).unwrap();
+        store
+            .cache
+            .insert("memory-key".to_string(), json!("memory"));
+
+        store.load_ignore_defaults().unwrap();
+
+        assert_eq!(store.get("disk-key"), Some(&json!("disk")));
+        assert_eq!(store.get("default-key"), None);
+        assert_eq!(store.get("memory-key"), None);
+
+        let _ = fs::remove_dir_all(path.parent().unwrap());
+    }
+}