Remove the `directories` dependency (#4904)

eframe now has its own logic to find the storage_dir to persist the app
when the persistence feature is enabled, instead of using the
directories crate. The directory should be the same as before (verified
with a unit test).

* Closes <https://github.com/emilk/egui/issues/4884>
* [x] I have followed the instructions in the PR template

Cargo.lock

@@ -1180,6 +1180,7 @@ dependencies = [
  "glow",
  "glutin",
  "glutin-winit",
+ "home",
  "image",
  "js-sys",
  "log",
@@ -1200,6 +1201,7 @@ dependencies = [
  "web-time",
  "wgpu",
  "winapi",
+ "windows-sys 0.52.0",
  "winit",
 ]
 
@@ -2059,11 +2061,11 @@ checksum = "dfa686283ad6dd069f105e5ab091b04c62850d3e4cf5d67debad1933f55023df"
 
 [[package]]
 name = "home"
-version = "0.5.5"
+version = "0.5.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5444c27eef6923071f7ebcc33e3444508466a76f7a2b93da00ed6e19f30c1ddb"
+checksum = "e3d1354bf6b7235cb4a0576c2619fd4ed18183f689b12b006a0ee7329eeff9a5"
 dependencies = [
- "windows-sys 0.48.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]

Cargo.toml

@@ -77,6 +77,7 @@ document-features = " 0.2.8"
 glow = "0.13"
 glutin = "0.32.0"
 glutin-winit = "0.5.0"
+home = "0.5.9"
 image = { version = "0.25", default-features = false }
 log = { version = "0.4", features = ["std"] }
 nohash-hasher = "0.2"
@@ -95,6 +96,7 @@ wgpu = { version = "22.1.0", default-features = false, features = [
     # Make the renderer `Sync` even on wasm32, because it makes the code simpler:
     "fragile-send-sync-non-atomic-wasm",
 ] }
+windows-sys = "0.52"
 winit = { version = "0.30.5", default-features = false }
 
 [workspace.lints.rust]

crates/eframe/Cargo.toml

@@ -63,7 +63,7 @@ glow = ["dep:egui_glow", "dep:glow", "dep:glutin-winit", "dep:glutin"]
 
 ## Enable saving app state to disk.
 persistence = [
-  "directories",
+  "dep:home",
   "egui-winit/serde",
   "egui/persistence",
   "ron",
@@ -148,7 +148,6 @@ image = { workspace = true, features = ["png"] } # Needed for app icon
 winit = { workspace = true, default-features = false, features = ["rwh_06"] }
 
 # optional native:
-directories = { version = "5", optional = true }
 egui-wgpu = { workspace = true, optional = true, features = [
   "winit",
 ] } # if wgpu is used, use it with winit
@@ -158,6 +157,7 @@ pollster = { version = "0.3", optional = true } # needed for wgpu
 # this can be done at the same time we expose x11/wayland features of winit crate.
 glutin = { workspace = true, optional = true }
 glutin-winit = { workspace = true, optional = true }
+home = { workspace = true, optional = true }
 puffin = { workspace = true, optional = true }
 wgpu = { workspace = true, optional = true, features = [
   # Let's enable some backends so that users can use `eframe` out-of-the-box
@@ -185,6 +185,7 @@ objc2-app-kit = { version = "0.2.0", features = [
 # windows:
 [target.'cfg(any(target_os = "windows"))'.dependencies]
 winapi = { version = "0.3.9", features = ["winuser"] }
+windows-sys = { workspace = true, features = ["Win32_Foundation", "Win32_UI_Shell", "Win32_System_Com"] }
 
 # -------------------------------------------
 # web:
@@ -253,3 +254,7 @@ wgpu = { workspace = true, optional = true, features = [
   # without having to explicitly opt-in to backends
   "webgpu",
 ] }
+
+# Native dev dependencies for testing
+[target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
+directories = "5"

crates/eframe/src/epi.rs

@@ -351,8 +351,8 @@ pub struct NativeOptions {
     /// persisted (only if the "persistence" feature is enabled).
     pub persist_window: bool,
 
-    /// The folder where `eframe` will store the app state. If not set, eframe will get the paths
-    /// from [directories].
+    /// The folder where `eframe` will store the app state. If not set, eframe will use a default
+    /// data storage path for each target system.
     pub persistence_path: Option<std::path::PathBuf>,
 
     /// Controls whether to apply dithering to minimize banding artifacts.

crates/eframe/src/native/file_storage.rs

@@ -10,13 +10,80 @@ use std::{
 /// [`egui::ViewportBuilder::app_id`] of [`crate::NativeOptions::viewport`]
 /// or the title argument to [`crate::run_native`].
 ///
-/// On native the path is picked using [`directories::ProjectDirs::data_dir`](https://docs.rs/directories/5.0.1/directories/struct.ProjectDirs.html#method.data_dir) which is:
+/// On native, the path is:
 /// * Linux:   `/home/UserName/.local/share/APP_ID`
 /// * macOS:   `/Users/UserName/Library/Application Support/APP_ID`
-/// * Windows: `C:\Users\UserName\AppData\Roaming\APP_ID`
+/// * Windows: `C:\Users\UserName\AppData\Roaming\APP_ID\data`
 pub fn storage_dir(app_id: &str) -> Option<PathBuf> {
-    directories::ProjectDirs::from("", "", app_id)
-        .map(|proj_dirs| proj_dirs.data_dir().to_path_buf())
+    use egui::os::OperatingSystem as OS;
+    use std::env::var_os;
+    match OS::from_target_os() {
+        OS::Nix => var_os("XDG_DATA_HOME")
+            .map(PathBuf::from)
+            .filter(|p| p.is_absolute())
+            .or_else(|| home::home_dir().map(|p| p.join(".local").join("share")))
+            .map(|p| {
+                p.join(
+                    app_id
+                        .to_lowercase()
+                        .replace(|c: char| c.is_ascii_whitespace(), ""),
+                )
+            }),
+        OS::Mac => home::home_dir().map(|p| {
+            p.join("Library")
+                .join("Application Support")
+                .join(app_id.replace(|c: char| c.is_ascii_whitespace(), "-"))
+        }),
+        OS::Windows => roaming_appdata().map(|p| p.join(app_id).join("data")),
+        OS::Unknown | OS::Android | OS::IOS => None,
+    }
+}
+
+// Adapted from
+// https://github.com/rust-lang/cargo/blob/6e11c77384989726bb4f412a0e23b59c27222c34/crates/home/src/windows.rs#L19-L37
+#[cfg(all(windows, not(target_vendor = "uwp")))]
+#[allow(unsafe_code)]
+fn roaming_appdata() -> Option<PathBuf> {
+    use std::ffi::OsString;
+    use std::os::windows::ffi::OsStringExt;
+    use std::ptr;
+    use std::slice;
+
+    use windows_sys::Win32::Foundation::S_OK;
+    use windows_sys::Win32::System::Com::CoTaskMemFree;
+    use windows_sys::Win32::UI::Shell::{
+        FOLDERID_RoamingAppData, SHGetKnownFolderPath, KF_FLAG_DONT_VERIFY,
+    };
+
+    extern "C" {
+        fn wcslen(buf: *const u16) -> usize;
+    }
+    unsafe {
+        let mut path = ptr::null_mut();
+        match SHGetKnownFolderPath(
+            &FOLDERID_RoamingAppData,
+            KF_FLAG_DONT_VERIFY as u32,
+            0,
+            &mut path,
+        ) {
+            S_OK => {
+                let path_slice = slice::from_raw_parts(path, wcslen(path));
+                let s = OsString::from_wide(&path_slice);
+                CoTaskMemFree(path.cast());
+                Some(PathBuf::from(s))
+            }
+            _ => {
+                // Free any allocated memory even on failure. A null ptr is a no-op for `CoTaskMemFree`.
+                CoTaskMemFree(path.cast());
+                None
+            }
+        }
+    }
+}
+
+#[cfg(any(not(windows), target_vendor = "uwp"))]
+fn roaming_appdata() -> Option<PathBuf> {
+    None
 }
 
 // ----------------------------------------------------------------------------
@@ -171,3 +238,23 @@ where
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn directories_storage_dir(app_id: &str) -> Option<PathBuf> {
+        directories::ProjectDirs::from("", "", app_id)
+            .map(|proj_dirs| proj_dirs.data_dir().to_path_buf())
+    }
+
+    #[test]
+    fn storage_path_matches_directories() {
+        use super::storage_dir;
+        for app_id in [
+            "MyApp", "My App", "my_app", "my-app", "My.App", "my/app", "my:app", r"my\app",
+        ] {
+            assert_eq!(directories_storage_dir(app_id), storage_dir(app_id));
+        }
+    }
+}