Web: warn before reloading a document with unsaved changes (#812) (#856)

apps/pdfcraft-web/Cargo.toml

@@ -16,5 +16,5 @@ egui = { workspace = true }
 
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 wasm-bindgen-futures = "0.4"
-web-sys = { version = "0.3", features = ["Window", "Document", "Element", "HtmlCanvasElement", "HtmlElement", "Location", "Url", "UrlSearchParams", "Response"] }
+web-sys = { version = "0.3", features = ["Window", "Document", "Element", "HtmlCanvasElement", "HtmlElement", "Location", "Url", "UrlSearchParams", "Response", "Event"] }
 js-sys = "0.3"

apps/pdfcraft-web/src/main.rs

@@ -51,6 +51,9 @@ fn main() {
                             ctx.request_repaint();
                         });
                     }
+                    // eframe never raises a close request on a browser reload or tab close, so `guard_quit` never
+                    // prompts; ask the browser to confirm instead while a document has unsaved work (#812).
+                    warn_before_unload(app.unsaved_flag.clone());
                     Ok(Box::new(app))
                 }),
             )
@@ -61,6 +64,20 @@ fn main() {
     });
 }
 
+#[cfg(target_arch = "wasm32")]
+fn warn_before_unload(unsaved: std::sync::Arc<std::sync::atomic::AtomicBool>) {
+    use eframe::wasm_bindgen::{JsCast, closure::Closure};
+    let Some(window) = web_sys::window() else { return };
+    let handler = Closure::<dyn FnMut(web_sys::Event)>::new(move |event: web_sys::Event| {
+        if unsaved.load(std::sync::atomic::Ordering::Relaxed) {
+            event.prevent_default();
+        }
+    });
+    if window.add_event_listener_with_callback("beforeunload", handler.as_ref().unchecked_ref()).is_ok() {
+        handler.forget();
+    }
+}
+
 #[cfg(target_arch = "wasm32")]
 fn query_param(key: &str) -> Option<String> {
     let search = web_sys::window()?.location().search().ok()?;

crates/ui-egui/src/editing.rs

@@ -590,8 +590,14 @@ impl PdfCraftApp {
         ctx.send_viewport_cmd(egui::ViewportCommand::Close);
     }
 
+    /// Publish whether any document has unsaved work, for the browser's reload warning (#812).
+    pub(crate) fn sync_unsaved_flag(&self) {
+        self.unsaved_flag.store(self.first_dirty().is_some(), std::sync::atomic::Ordering::Relaxed);
+    }
+
     /// Intercept window close while documents have unsaved changes.
     pub(crate) fn guard_quit(&mut self, ctx: &egui::Context) {
+        self.sync_unsaved_flag();
         if !ctx.input(|i| i.viewport().close_requested()) {
             return;
         }
@@ -926,6 +932,19 @@ mod revert_draft_tests {
         assert!(app.views[index].forms.committed.is_some() && app.views[index].pending_edit.is_some());
     }
 
+    #[test]
+    fn unsaved_flag_follows_dirty_state() {
+        use std::sync::atomic::Ordering;
+        // `guard_quit` runs every frame, also on the web, where no close request ever arrives.
+        let ctx = egui::Context::default();
+        let mut app = app();
+        app.guard_quit(&ctx);
+        assert!(!app.unsaved_flag.load(Ordering::Relaxed));
+        assert!(app.apply_edit(Edit::SetFieldValue { name: "name".into(), value: FieldValue::Text("Changed".into()) }));
+        app.guard_quit(&ctx);
+        assert!(app.unsaved_flag.load(Ordering::Relaxed));
+    }
+
     #[test]
     fn successful_revert_clears_focused_or_queued_drafts_only_on_its_document() {
         for queued in [false, true] {

crates/ui-egui/src/lib.rs

@@ -424,6 +424,8 @@ pub struct PdfCraftApp {
     startup_superseded: bool,
     /// Asynchronous opens that failed (web `?file=` fetches), shown as a notice.
     pub failed_inbox: FailedInbox,
+    /// Mirrors "some document has unsaved work" each frame, so the web page's `beforeunload` handler can read it (#812).
+    pub unsaved_flag: std::sync::Arc<std::sync::atomic::AtomicBool>,
     /// Requests from the operating system, polled every frame (macOS Apple events).
     pub os_events: Option<OsEventsFn>,
     /// A pending "save changes?" question (closing a dirty tab or quitting).
@@ -689,6 +691,7 @@ impl PdfCraftApp {
             startup_inbox: Default::default(),
             startup_superseded: false,
             failed_inbox: Default::default(),
+            unsaved_flag: Default::default(),
             os_events: None,
             close_request: None,
             save_override: None,