From a0ec1fb785ab17d084ac76d5ad41024169d32214 Mon Sep 17 00:00:00 2001
From: DCM4711 <107349915+DCM4711@users.noreply.github.com>
Date: Wed, 14 Oct 2026 20:24:56 +0200
Subject: [PATCH] Selection: whole columns and rows don't widen to merged cells

Clicking column B's header on a sheet with A2:C2 merged selected A:C,
because selection.set grows every area until merged cells are whole.
Excel leaves header selections alone: column B stays B:B and row 3 stays
3:3. Cell ranges still take merged cells whole (B1:B3 -> A1:C3).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 crates/engine/src/selection.rs |  6 +++++-
 crates/engine/src/tests.rs     | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/crates/engine/src/selection.rs b/crates/engine/src/selection.rs
index 27418a21a..4df6fbe4a 100644
--- a/crates/engine/src/selection.rs
+++ b/crates/engine/src/selection.rs
@@ -63,9 +63,13 @@ impl Selection {
     pub fn a1(&self) -> String {
         self.ranges.iter().map(|r| r.a1()).collect::<Vec<_>>().join(",")
     }
-    /// Expands areas so merged cells are included whole.
+    /// Expands areas so merged cells are included whole. Whole columns and whole rows stay as
+    /// they are: clicking column B's header selects just B even when B1:C1 is merged, as in Excel.
     pub fn expand_merges(&mut self, sheet: &Sheet) {
         for r in self.ranges.iter_mut() {
+            if r.is_full_cols() || r.is_full_rows() {
+                continue;
+            }
             let mut cur = *r;
             loop {
                 let mut grown = cur;
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index ae499a189..9051d29e4 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -2267,6 +2267,21 @@ fn whole_sheet_selection_stays_within_the_data() {
     assert!(s.execute("data.removeDuplicates", json!({"range": "A1:XFD1048576", "header": false})).is_ok());
 }
 
+#[test]
+fn whole_columns_and_rows_ignore_merges_but_cell_ranges_take_them_whole() {
+    // As in Excel: a merged A2:C2 doesn't widen a click on column B's header to A:C, nor a
+    // merged B2:B4 a click on row 3's header to rows 2:4; a cell range still takes them whole.
+    let mut s = s();
+    s.execute("home.mergeCenter", json!({"range": "A2:C2"})).unwrap();
+    s.execute("home.mergeCenter", json!({"range": "E2:E4"})).unwrap();
+    let sel = |s: &mut Session, range: &str| s.execute("selection.set", json!({"range": range})).unwrap()["selection"].clone();
+    assert_eq!(sel(&mut s, "B:B"), "B:B");
+    assert_eq!(sel(&mut s, "A:B"), "A:B");
+    assert_eq!(sel(&mut s, "3:3"), "3:3");
+    assert_eq!(sel(&mut s, "B1:B3"), "A1:C3");
+    assert_eq!(sel(&mut s, "E3"), "E2:E4");
+}
+
 #[test]
 fn parity_counts() {
     let (done, total) = crate::catalog::parity();