Add `eframe::storage_dir` (#3286)

* Add `eframe::storage_dir`

Now you can easily tell where eframe stores its state

* egui_plot: work even without the `serde` featur flag

crates/eframe/src/epi/mod.rs

@@ -139,13 +139,8 @@ pub trait App {
     /// Only called when the "persistence" feature is enabled.
     ///
     /// On web the state is stored to "Local Storage".
-    /// On native the path is picked using [`directories_next::ProjectDirs::data_dir`](https://docs.rs/directories-next/2.0.0/directories_next/struct.ProjectDirs.html#method.data_dir) which is:
-    /// * Linux:   `/home/UserName/.local/share/APP_ID`
-    /// * macOS:   `/Users/UserName/Library/Application Support/APP_ID`
-    /// * Windows: `C:\Users\UserName\AppData\Roaming\APP_ID`
     ///
-    /// where `APP_ID` is determined by either [`NativeOptions::app_id`] or
-    /// the title argument to [`crate::run_native`].
+    /// On native the path is picked using [`crate::storage_dir`].
     fn save(&mut self, _storage: &mut dyn Storage) {}
 
     /// Called when the user attempts to close the desktop window and/or quit the application.
@@ -422,13 +417,10 @@ pub struct NativeOptions {
 
     /// The application id, used for determining the folder to persist the app to.
     ///
-    /// On native the path is picked using [`directories_next::ProjectDirs::data_dir`](https://docs.rs/directories-next/2.0.0/directories_next/struct.ProjectDirs.html#method.data_dir) which is:
-    /// * Linux:   `/home/UserName/.local/share/APP_ID`
-    /// * macOS:   `/Users/UserName/Library/Application Support/APP_ID`
-    /// * Windows: `C:\Users\UserName\AppData\Roaming\APP_ID`
+    /// On native the path is picked using [`crate::storage_dir`].
     ///
     /// If you don't set [`Self::app_id`], the title argument to [`crate::run_native`]
-    /// will be used instead.
+    /// will be used as app id instead.
     ///
     /// ### On Wayland
     /// On Wayland this sets the Application ID for the window.

crates/eframe/src/lib.rs

@@ -159,6 +159,11 @@ pub use web::{WebLogger, WebRunner};
 #[cfg(any(feature = "glow", feature = "wgpu"))]
 mod native;
 
+#[cfg(not(target_arch = "wasm32"))]
+#[cfg(any(feature = "glow", feature = "wgpu"))]
+#[cfg(feature = "persistence")]
+pub use native::file_storage::storage_dir;
+
 /// This is how you start a native (desktop) app.
 ///
 /// The first argument is name of your app, used for the title bar of the native window

crates/eframe/src/native/epi_integration.rs

@@ -331,7 +331,7 @@ pub fn handle_app_output(
 /// For loading/saving app state and/or egui memory to disk.
 pub fn create_storage(_app_name: &str) -> Option<Box<dyn epi::Storage>> {
     #[cfg(feature = "persistence")]
-    if let Some(storage) = super::file_storage::FileStorage::from_app_name(_app_name) {
+    if let Some(storage) = super::file_storage::FileStorage::from_app_id(_app_name) {
         return Some(Box::new(storage));
     }
     None

crates/eframe/src/native/file_storage.rs

@@ -3,6 +3,20 @@ use std::{
     path::{Path, PathBuf},
 };
 
+/// The folder where `eframe` will store its state.
+///
+/// The given `app_id` is either [`crate::NativeOptions::app_id`] or
+/// the title argument to [`crate::run_native`].
+///
+/// On native the path is picked using [`directories_next::ProjectDirs::data_dir`](https://docs.rs/directories-next/2.0.0/directories_next/struct.ProjectDirs.html#method.data_dir) which is:
+/// * Linux:   `/home/UserName/.local/share/APP_ID`
+/// * macOS:   `/Users/UserName/Library/Application Support/APP_ID`
+/// * Windows: `C:\Users\UserName\AppData\Roaming\APP_ID`
+pub fn storage_dir(app_id: &str) -> Option<PathBuf> {
+    directories_next::ProjectDirs::from("", "", app_id)
+        .map(|proj_dirs| proj_dirs.data_dir().to_path_buf())
+}
+
 // ----------------------------------------------------------------------------
 
 /// A key-value store backed by a [RON](https://github.com/ron-rs/ron) file on disk.
@@ -24,7 +38,7 @@ impl Drop for FileStorage {
 
 impl FileStorage {
     /// Store the state in this .ron file.
-    pub fn from_ron_filepath(ron_filepath: impl Into<PathBuf>) -> Self {
+    fn from_ron_filepath(ron_filepath: impl Into<PathBuf>) -> Self {
         let ron_filepath: PathBuf = ron_filepath.into();
         log::debug!("Loading app state from {:?}…", ron_filepath);
         Self {
@@ -36,9 +50,8 @@ impl FileStorage {
     }
 
     /// Find a good place to put the files that the OS likes.
-    pub fn from_app_name(app_name: &str) -> Option<Self> {
-        if let Some(proj_dirs) = directories_next::ProjectDirs::from("", "", app_name) {
-            let data_dir = proj_dirs.data_dir().to_path_buf();
+    pub fn from_app_id(app_id: &str) -> Option<Self> {
+        if let Some(data_dir) = storage_dir(app_id) {
             if let Err(err) = std::fs::create_dir_all(&data_dir) {
                 log::warn!(
                     "Saving disabled: Failed to create app path at {:?}: {}",

crates/egui_plot/src/lib.rs

@@ -126,6 +126,7 @@ struct PlotMemory {
     last_click_pos_for_zoom: Option<Pos2>,
 }
 
+#[cfg(feature = "serde")]
 impl PlotMemory {
     pub fn load(ctx: &Context, id: Id) -> Option<Self> {
         ctx.data_mut(|d| d.get_persisted(id))
@@ -136,6 +137,17 @@ impl PlotMemory {
     }
 }
 
+#[cfg(not(feature = "serde"))]
+impl PlotMemory {
+    pub fn load(ctx: &Context, id: Id) -> Option<Self> {
+        ctx.data_mut(|d| d.get_temp(id))
+    }
+
+    pub fn store(self, ctx: &Context, id: Id) {
+        ctx.data_mut(|d| d.insert_temp(id, self));
+    }
+}
+
 // ----------------------------------------------------------------------------
 
 /// Indicates a vertical or horizontal cursor line in plot coordinates.