From baac184ed87e55642527b72e37c194e8ae32f82d Mon Sep 17 00:00:00 2001
From: MarekSpodBiedry <73122968+MarekSpodBiedry@users.noreply.github.com>
Date: Mon, 12 Oct 2026 08:31:22 +0200
Subject: [PATCH] Reject row/column insert counts past the worksheet and clamp
 delete counts instead of overflowing (#531)

---
 crates/engine/src/cmd/sheet.rs             |  9 ++++-
 crates/engine/tests/line_count_overflow.rs | 47 ++++++++++++++++++++++
 2 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 crates/engine/tests/line_count_overflow.rs

diff --git a/crates/engine/src/cmd/sheet.rs b/crates/engine/src/cmd/sheet.rs
index f05b77d91..48209050a 100644
--- a/crates/engine/src/cmd/sheet.rs
+++ b/crates/engine/src/cmd/sheet.rs
@@ -249,10 +249,14 @@ fn cancel_copy_mode(s: &mut Session) {
 
 fn insert_lines(s: &mut Session, p: &Json, axis: Axis) -> Result<Json> {
     let (at, count) = lines(s, p, axis)?;
+    let limit = if axis == Axis::Rows { MAX_ROWS } else { MAX_COLS };
+    if at.checked_add(count).is_none_or(|end| end > limit) {
+        let cmd = if axis == Axis::Rows { "home.insertRows" } else { "home.insertColumns" };
+        return Err(bad(cmd, "the inserted lines would extend past the end of the worksheet"));
+    }
     check_lines_protection(s, p, axis, at, count, true)?;
     let sheet = target_sheet(s, p)?;
     // Refuse to push data off the sheet.
-    let limit = if axis == Axis::Rows { MAX_ROWS } else { MAX_COLS };
     if let Some(u) = s.doc()?.wb.sheet(sheet).and_then(|sh| sh.used_range()) {
         let last = if axis == Axis::Rows { u.end.row } else { u.end.col };
         if last >= at && last as u64 + count as u64 >= limit as u64 {
@@ -290,6 +294,9 @@ fn insert_lines(s: &mut Session, p: &Json, axis: Axis) -> Result<Json> {
 
 fn delete_lines(s: &mut Session, p: &Json, axis: Axis) -> Result<Json> {
     let (at, count) = lines(s, p, axis)?;
+    let limit = if axis == Axis::Rows { MAX_ROWS } else { MAX_COLS };
+    // Deleting past the last line only removes up to the end of the worksheet.
+    let count = count.min(limit.saturating_sub(at)).max(1);
     check_lines_protection(s, p, axis, at, count, false)?;
     let sheet = target_sheet(s, p)?;
     let out = edit(s, |cx| {
diff --git a/crates/engine/tests/line_count_overflow.rs b/crates/engine/tests/line_count_overflow.rs
new file mode 100644
index 000000000..9ae58d1a9
--- /dev/null
+++ b/crates/engine/tests/line_count_overflow.rs
@@ -0,0 +1,47 @@
+use gridcraft_engine::{EngineError, Session};
+use serde_json::json;
+
+fn session() -> Session {
+    let mut session = Session::new();
+    session.new_workbook();
+    session
+}
+
+#[test]
+fn insert_with_an_out_of_range_count_is_a_normal_error() {
+    for (id, key, at) in [("home.insertRows", "rows", "3:3"), ("home.insertColumns", "cols", "C:C")] {
+        let mut session = session();
+        let err = session.execute(id, json!({ key: at, "count": u32::MAX })).unwrap_err();
+        assert!(matches!(err, EngineError::BadParams { .. }), "{id}: {err:?}");
+    }
+}
+
+#[test]
+fn insert_after_a_formatted_line_with_an_out_of_range_count_is_a_normal_error() {
+    // A custom size on the preceding line and no cells: the used-range guard has nothing to check.
+    let mut session = session();
+    session.execute("home.rowHeight", json!({"rows": "2:2", "height": 30})).unwrap();
+    let err = session.execute("home.insertRows", json!({"rows": "3:3", "count": u32::MAX})).unwrap_err();
+    assert!(matches!(err, EngineError::BadParams { .. }), "{err:?}");
+
+    let mut session = session();
+    session.execute("home.columnWidth", json!({"cols": "B:B", "width": 100})).unwrap();
+    let err = session.execute("home.insertColumns", json!({"cols": "C:C", "count": u32::MAX})).unwrap_err();
+    assert!(matches!(err, EngineError::BadParams { .. }), "{err:?}");
+}
+
+#[test]
+fn delete_with_an_out_of_range_count_does_not_panic() {
+    for (id, key, at) in [("home.deleteRows", "rows", "3:3"), ("home.deleteColumns", "cols", "C:C")] {
+        let mut session = session();
+        let res = session.execute(id, json!({ key: at, "count": u32::MAX }));
+        assert!(!matches!(res, Err(EngineError::Internal(..))), "{id}: {res:?}");
+    }
+}
+
+#[test]
+fn insert_and_delete_with_a_small_count_still_work() {
+    let mut session = session();
+    session.execute("home.insertRows", json!({"rows": "1:1", "count": 3})).unwrap();
+    session.execute("home.deleteRows", json!({"rows": "1:1", "count": 3})).unwrap();
+}