#3136: ask before a drag and drop replaces data

Dragging the selection's border onto cells that hold data replaced them
without asking, so dragging column B onto column A silently destroyed A.
Excel asks "There's already data here. Do you want to replace it?" first
(its "Alert before overwriting cells" option, on by default).

The drop now runs a new `range.move {range?, to, overwrite?}` command:
a cut and paste that returns a confirm question when the destination
holds data other than the moved cells; the grid shows it with OK and
Cancel, and OK runs it again with `overwrite: true`. A refused move
leaves the sheet and the clipboard as they were.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/edit/clipboard.rs

@@ -1,7 +1,8 @@
 use super::cell::input_to_cell;
 use super::paste_special::paste_special;
 use super::{
-    Cell, Clipboard, EngineError, Json, RangeRef, Result, Session, Value, cell_param_on, edit, json, ok, str_param, target_ranges, target_sheet,
+    Cell, Clipboard, EngineError, Json, RangeRef, Result, Session, Value, bad, bool_param, cell_param_on, edit, json, ok, str_param, target_ranges,
+    target_sheet,
 };
 
 // ---------------------------------------------------------------- clipboard
@@ -163,6 +164,32 @@ pub(super) fn paste(s: &mut Session, p: &Json) -> Result<Json> {
     paste_special(s, &json!({"what": "all", "at": p.get("at").cloned().unwrap_or(Json::Null)}))
 }
 
+/// Drag and drop (dragging the selection's border): moves `range` so its top-left cell lands on
+/// `to`, as Cut and Paste would. Like Excel, it asks before replacing cells that hold data (other
+/// than the moved cells themselves); run it again with `overwrite: true` to replace them. A
+/// refused or failed move leaves the clipboard as it was.
+pub(super) fn range_move(s: &mut Session, p: &Json) -> Result<Json> {
+    let sheet = target_sheet(s, p)?;
+    let to = cell_param_on(s, p, "to", sheet)?.ok_or_else(|| bad("range.move", "missing `to`"))?;
+    let kept = s.clipboard.take();
+    let moved = cut(s, p).and_then(|_| {
+        let src = s.clipboard.as_ref().map(|c| c.range).unwrap_or_default();
+        let dest = to.offset(i64::from(src.height()) - 1, i64::from(src.width()) - 1).map(|end| RangeRef::new(to, end));
+        if bool_param(p, "overwrite") != Some(true)
+            && let Some(dest) = dest
+            && let Some(sh) = s.doc()?.wb.sheet(sheet)
+            && sh.cells.iter_range(dest).any(|(c, cell)| !src.contains(c) && cell.has_content())
+        {
+            return Err(EngineError::Confirm("There's already data here. Do you want to replace it?".into()));
+        }
+        paste(s, &json!({"at": to.a1()}))
+    });
+    if moved.is_err() {
+        s.clipboard = kept;
+    }
+    moved
+}
+
 fn paste_text(s: &mut Session, p: &Json, text: &str) -> Result<Json> {
     let sheet = target_sheet(s, p)?;
     let at = cell_param_on(s, p, "at", sheet)?.unwrap_or(s.doc()?.selection.current().start);

crates/engine/src/cmd/edit/tests.rs

@@ -353,6 +353,34 @@ fn cut_paste_that_overflows_the_grid_moves_nothing() {
     assert_eq!(get(&mut s, "XFD2")["value"], json!(2.0));
 }
 
+#[test]
+fn drag_and_drop_asks_before_replacing_data() {
+    // #3136: dragging column B's border onto column A replaced A without asking.
+    let mut s = Session::new();
+    s.new_workbook();
+    s.execute("range.setValues", json!({"range": "A1:B3", "values": [["Apple", "Kiwi"], ["Pear", "Plum"], ["Fig", "Lime"]]})).unwrap();
+    s.execute("edit.copy", json!({"range": "D9"})).unwrap();
+    let text = |s: &mut Session, a: &str| s.execute("cell.get", json!({"cell": a})).unwrap()["input"].clone();
+    let r = s.execute("range.move", json!({"range": "B:B", "to": "A1"}));
+    let Err(EngineError::Confirm(q)) = r else { panic!("{r:?}") };
+    assert_eq!(q, "There's already data here. Do you want to replace it?");
+    // Nothing moved, and the copy made before is still on the clipboard.
+    assert_eq!(text(&mut s, "A1"), json!("Apple"));
+    assert_eq!(text(&mut s, "B1"), json!("Kiwi"));
+    assert!(s.clipboard.as_ref().is_some_and(|c| !c.cut && c.range.a1() == "D9"));
+    // Confirmed, column B replaces column A.
+    s.execute("range.move", json!({"range": "B:B", "to": "A1", "overwrite": true})).unwrap();
+    assert_eq!(text(&mut s, "A1"), json!("Kiwi"));
+    assert_eq!(text(&mut s, "A3"), json!("Lime"));
+    assert_eq!(text(&mut s, "B1"), json!(""));
+    // Onto empty cells, or overlapping only the moved cells themselves, nothing is asked.
+    s.execute("range.move", json!({"range": "A1:A3", "to": "A2"})).unwrap();
+    assert_eq!(text(&mut s, "A4"), json!("Lime"));
+    s.execute("range.move", json!({"range": "A2:A4", "to": "C2"})).unwrap();
+    assert_eq!(text(&mut s, "C2"), json!("Kiwi"));
+    assert!(s.execute("range.move", json!({"range": "C2"})).is_err(), "`to` is required");
+}
+
 #[test]
 fn replace_case_insensitive() {
     assert_eq!(replace_ci("Apple apple APPLE", "apple", "pear"), "pear pear pear");