Backspace still erases while Shift is held (#707) (#747)

Co-authored-by: Brandon Thomas <echelon@gmail.com>

crates/ui-egui/src/keys.rs

@@ -112,17 +112,29 @@ fn dispatch(app: &mut WordApp, key: Key, m: Modifiers) -> bool {
         let _ = app.run(spec.id, json!({}));
         return true;
     }
-    // Shift extends caret movement.
+    // Shift extends caret movement; Shift+Backspace still erases (#707).
     if m.shift
         && let Some(spec) = app.session.keymap.resolve(&reg, &combo(m, name, false))
-        && spec.id.starts_with("caret.")
+        && let Some(params) = shift_variant_params(spec.id)
     {
-        let _ = app.run(spec.id, json!({"extend": true}));
+        let _ = app.run(spec.id, params);
         return true;
     }
     false
 }
 
+/// How a command bound to a plain key runs when Shift is also held and nothing is bound to the
+/// shifted combo: caret moves extend the selection, Backspace erases as usual (#707).
+fn shift_variant_params(id: &str) -> Option<Value> {
+    if id.starts_with("caret.") {
+        Some(json!({"extend": true}))
+    } else if id == "text.backspace" {
+        Some(json!({}))
+    } else {
+        None
+    }
+}
+
 /// F1–F12: shortcuts on these work without the canvas focused.
 fn is_function_key(key: Key) -> bool {
     matches!(key, Key::F1 | Key::F2 | Key::F3 | Key::F4 | Key::F5 | Key::F6 | Key::F7 | Key::F8 | Key::F9 | Key::F10 | Key::F11 | Key::F12)
@@ -322,6 +334,13 @@ pub fn global_shortcuts(app: &mut WordApp, ctx: &egui::Context) {
 mod tests {
     use super::*;
 
+    #[test]
+    fn shift_backspace_still_erases() {
+        assert_eq!(shift_variant_params("text.backspace"), Some(json!({})));
+        assert_eq!(shift_variant_params("caret.left"), Some(json!({"extend": true})));
+        assert_eq!(shift_variant_params("text.delete"), None);
+    }
+
     #[test]
     fn only_plain_paste_releases_paste_a_clipboard_picture() {
         let m = |command, shift, alt| egui::Modifiers { command, shift, alt, ..Default::default() };