Add cache_version flag to saved state

Can be used to determine whether the cache file format has been broken after an update.
If so, the cache will be discarded and recreated.

src/library.rs

@@ -10,8 +10,8 @@ use rspotify::model::Id;
 use serde::de::DeserializeOwned;
 use serde::Serialize;
 
-use crate::config;
 use crate::config::Config;
+use crate::config::{self, CACHE_VERSION};
 use crate::events::EventManager;
 use crate::model::album::Album;
 use crate::model::artist::Artist;
@@ -70,13 +70,22 @@ impl Library {
     }
 
     fn load_cache<T: DeserializeOwned>(&self, cache_path: PathBuf, store: Arc<RwLock<Vec<T>>>) {
+        let saved_cache_version = self.cfg.state().cache_version;
+        if saved_cache_version < CACHE_VERSION {
+            debug!(
+                "Cache version for {:?} has changed from {} to {}, ignoring cache",
+                cache_path, saved_cache_version, CACHE_VERSION
+            );
+            return;
+        }
+
         if let Ok(contents) = std::fs::read_to_string(&cache_path) {
             debug!("loading cache from {}", cache_path.display());
             let parsed: Result<Vec<T>, _> = serde_json::from_str(&contents);
             match parsed {
                 Ok(cache) => {
                     debug!(
-                        "cache from {} loaded ({} lists)",
+                        "cache from {} loaded ({} items)",
                         cache_path.display(),
                         cache.len()
                     );