feat: add remove_string() to storage trait (#8264)

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This PR adds a `remove_string()` API to the Storage trait and also
implements it in the `FileStorage` and `LocalStorage` stucts.

crates/eframe/src/epi.rs

@@ -942,6 +942,9 @@ pub trait Storage {
     /// Set the value for the given key.
     fn set_string(&mut self, key: &str, value: String);
 
+    /// Remove a given key.
+    fn remove_string(&mut self, key: &str);
+
     /// write-to-disk or similar
     fn flush(&mut self);
 }

crates/eframe/src/native/file_storage.rs

@@ -159,6 +159,11 @@ impl crate::Storage for FileStorage {
         }
     }
 
+    fn remove_string(&mut self, key: &str) {
+        self.kv.remove(key);
+        self.dirty = true;
+    }
+
     fn flush(&mut self) {
         if self.dirty {
             profiling::scope!("FileStorage::flush");

crates/eframe/src/web/app_runner.rs

@@ -431,5 +431,9 @@ impl epi::Storage for LocalStorage {
         super::storage::local_storage_set(key, &value);
     }
 
+    fn remove_string(&mut self, key: &str) {
+        super::storage::local_storage_remove(key);
+    }
+
     fn flush(&mut self) {}
 }

crates/eframe/src/web/storage.rs

@@ -24,6 +24,23 @@ pub fn local_storage_set(key: &str, value: &str) {
     }
 }
 
+/// Remove data from local storage.
+pub fn local_storage_remove(key: &str) {
+    match local_storage() {
+        Some(storage) => {
+            if let Err(err) = storage.remove_item(key) {
+                log::warn!(
+                    "local_storage_remove failed: key={key}, err={}",
+                    crate::web::string_from_js_value(&err)
+                );
+            }
+        }
+        None => {
+            log::warn!("local_storage unavailable");
+        }
+    }
+}
+
 #[cfg(feature = "persistence")]
 pub(crate) fn load_memory(ctx: &egui::Context) {
     if let Some(memory_string) = local_storage_get("egui_memory_ron") {