Shift+Arrow on a whole column or row keeps the view on the rows or columns it showed (fixes #2451)

crates/ui-egui/src/grid.rs

@@ -701,9 +701,14 @@ pub fn show(app: &mut SheetApp, ui: &mut egui::Ui) {
     // Keep the active cell (or the moving end of an extension) visible after keyboard moves.
     if app.grid.ensure_visible {
         app.grid.ensure_visible = false;
-        let cell = if std::mem::take(&mut app.grid.reveal_moving_end) { sel.moving_end() } else { sel.active };
+        let moving = std::mem::take(&mut app.grid.reveal_moving_end);
+        let cell = if moving { sel.moving_end() } else { sel.active };
         let from = app.grid.reveal_from.take();
         let target = app.editor.as_ref().and_then(|e| e.point_cell).unwrap_or(cell);
+        // A whole column's moving end sits on the sheet's last row (a whole row's on its last
+        // column): extending it only moves across, so the view keeps its place the other way.
+        let extended = (moving && target == cell).then(|| sel.current());
+        let before = view.scroll;
         if paper {
             crate::paper_view::ensure_covers(app, &wb, si, target);
             geo = make_geo(app, view.scroll);
@@ -731,6 +736,12 @@ pub fn show(app: &mut SheetApp, ui: &mut egui::Ui) {
         } else if from.is_some_and(|f| f.col >= geo.fc) {
             view.scroll.x = 0.0;
         }
+        if extended.is_some_and(|r| r.is_full_cols()) {
+            view.scroll.y = before.y;
+        }
+        if extended.is_some_and(|r| r.is_full_rows()) {
+            view.scroll.x = before.x;
+        }
         view.scroll = view.scroll.max(egui::Vec2::ZERO);
         geo = make_geo(app, view.scroll);
     }

crates/ui-egui/tests/it/selection_scroll.rs

@@ -290,3 +290,47 @@ fn down_from_a_frozen_header_row_goes_to_row_2_at_the_top_from_far_down() {
     assert_eq!(scroll(&h).y, 0.0);
     assert!(visible(&h, "A2"));
 }
+
+#[test]
+fn shift_arrows_on_a_whole_column_leave_the_rows_where_they_are() {
+    // A whole column's moving end is on the sheet's last row: Shift+Right from Ctrl+Space must
+    // widen it to the next columns without scrolling down to the bottom of the sheet.
+    let mut h = harness();
+    h.state_mut().session.execute("selection.set", json!({"cell": "A100"})).unwrap();
+    h.state_mut().grid.ensure_visible = true;
+    h.run_steps(2);
+    let down = scroll(&h).y;
+    assert!(down > 0.0 && visible(&h, "A100"));
+    h.state_mut().session.execute("selection.column", json!({})).unwrap();
+    h.run_steps(2);
+    key(&mut h, Key::ArrowRight, Modifiers::SHIFT);
+    assert_eq!(h.state().session.active().unwrap().selection.current(), RangeRef::parse("A:B").unwrap());
+    assert_eq!(scroll(&h).y, down, "the view stays on the rows it showed");
+    // The columns still scroll to follow the extension.
+    for _ in 0..30 {
+        key(&mut h, Key::ArrowRight, Modifiers::SHIFT);
+    }
+    assert!(visible(&h, "AF100") && !visible(&h, "A100"));
+    assert_eq!(scroll(&h).y, down);
+}
+
+#[test]
+fn shift_arrows_on_a_whole_row_leave_the_columns_where_they_are() {
+    let mut h = harness();
+    h.state_mut().session.execute("selection.set", json!({"cell": "CA1"})).unwrap();
+    h.state_mut().grid.ensure_visible = true;
+    h.run_steps(2);
+    let right = scroll(&h).x;
+    assert!(right > 0.0 && visible(&h, "CA1"));
+    h.state_mut().session.execute("selection.row", json!({})).unwrap();
+    h.run_steps(2);
+    key(&mut h, Key::ArrowDown, Modifiers::SHIFT);
+    assert_eq!(h.state().session.active().unwrap().selection.current(), RangeRef::parse("1:2").unwrap());
+    assert_eq!(scroll(&h).x, right, "the view stays on the columns it showed");
+    // The rows still scroll to follow the extension.
+    for _ in 0..60 {
+        key(&mut h, Key::ArrowDown, Modifiers::SHIFT);
+    }
+    assert!(visible(&h, "CA62") && !visible(&h, "CA1"));
+    assert_eq!(scroll(&h).x, right);
+}