Show a Cancel mnemonic on the unsaved-changes prompt. (#4622)

Windows and Linux already marked Yes and No. Cancel had no letter, so the prompt now shows (C)ancel and C cancels. macOS still hides the letters and keeps the shortcut. (#4582)

Co-authored-by: Brandon Thomas <[email protected]>

crates/ui-egui/src/discard_ui.rs

@@ -249,7 +249,9 @@ pub fn show(app: &mut PhotocraftApp, ctx: &egui::Context) {
     // The answers in the platform's words; `dialog_buttons` puts them in its order. Windows (and
     // Linux) ask Yes / No / Cancel with Y, N and Esc, as Photoshop does there; macOS asks
     // Don't Save / Cancel / Save. Esc always cancels (the modal closes on it).
-    let cancel = (ButtonRole::Cancel, "Cancel", mac.then_some(Key::C), 84.0, Answer::Cancel);
+    // Yes/No already show Y/N. Cancel gets C on every platform (#4582). macOS still hides the
+    // letters and keeps the shortcut.
+    let cancel = (ButtonRole::Cancel, "Cancel", Some(Key::C), 84.0, Answer::Cancel);
     let buttons = if reverts {
         vec![(ButtonRole::Default, "Revert", Some(Key::R), 84.0, Answer::Discard), cancel]
     } else if mac {
@@ -506,18 +508,14 @@ mod tests {
     fn windows_and_linux_ask_yes_no_cancel_with_the_default_first() {
         for os in [egui::os::OperatingSystem::Windows, egui::os::OperatingSystem::Nix] {
             let mut h = prompt_on(os);
-            let labels = ["(Y)es", "(N)o", "Cancel"];
+            let labels = ["(Y)es", "(N)o", "(C)ancel"];
             assert_eq!(drawn_order(&h, labels), labels, "{os:?}");
             tab_walks(&mut h, labels);
             h.key_press(Key::N);
             h.run_steps(2);
             assert_eq!(docs_left(&h), Some(1), "N answered the first document");
-            // Cancel has no letter here: C does nothing, Esc cancels.
             h.key_press(Key::C);
             h.run_steps(2);
-            assert_eq!(docs_left(&h), Some(1));
-            h.key_press(Key::Escape);
-            h.run_steps(2);
             assert!(h.state().discard.is_none());
             assert_eq!(h.state().session.documents().len(), 1, "Cancel keeps the unanswered document");
         }
@@ -584,6 +582,7 @@ mod tests {
         assert_eq!(button_label(true, "Don't Save", Some(Key::D)), tl!("Don't Save"));
         assert_eq!(button_label(true, "Cancel", Some(Key::C)), tl!("Cancel"));
         assert_eq!(button_label(false, "Don't Save", Some(Key::D)), "(D)on't Save");
+        assert_eq!(button_label(false, "Cancel", Some(Key::C)), "(C)ancel");
     }
 
     #[test]