From 79a4cbac57e4a708e2a8e339ec0ec7ecb7788116 Mon Sep 17 00:00:00 2001
From: "Dylan M. Taylor" <dylan@dylanmtaylor.com>
Date: Tue, 3 Nov 2026 19:01:13 +0000
Subject: [PATCH] FORMULATEXT and the cell editor keep a hidden formula's
 source hidden

---
 crates/calc/src/eval/call.rs      |  9 ++++++---
 crates/engine/src/tests.rs        | 13 +++++++++++++
 crates/ui-egui/src/app/editing.rs |  5 +++++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/crates/calc/src/eval/call.rs b/crates/calc/src/eval/call.rs
index 08d563d43..64300188f 100644
--- a/crates/calc/src/eval/call.rs
+++ b/crates/calc/src/eval/call.rs
@@ -52,13 +52,16 @@ impl<'h> Evaluator<'h> {
             "ISFORMULA" | "FORMULATEXT" => {
                 let Some(Ev::R(a)) = args.first().map(|a| self.eval(a)) else { return err(CellError::NA) };
                 let Some(a) = a.first() else { return err(CellError::NA) };
-                let f = self.host.workbook().sheet(a.sheet).and_then(|s| s.cell(a.range.start)).and_then(|c| c.formula.clone());
+                let wb = self.host.workbook();
+                let f = wb.sheet(a.sheet).and_then(|s| s.cell(a.range.start)).and_then(|c| c.formula.clone());
+                // A formula formatted Hidden on a protected sheet stays hidden from FORMULATEXT too.
+                let hidden = wb.sheet(a.sheet).is_some_and(|s| s.is_protected() && wb.styles.get(s.style_id(a.range.start)).protection.hidden);
                 if name == "ISFORMULA" {
                     Ev::V(Value::Bool(f.is_some()))
                 } else {
                     match f {
-                        Some(f) => Ev::V(Value::text(format!("={}", f.text))),
-                        None => err(CellError::NA),
+                        Some(f) if !hidden => Ev::V(Value::text(format!("={}", f.text))),
+                        _ => err(CellError::NA),
                     }
                 }
             }
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index fe42b6977..a811b01b9 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -5572,3 +5572,16 @@ fn clearing_links_and_notes_keeps_allow_edit_ranges() {
     let sh = s.doc().unwrap().wb.active().unwrap().clone();
     assert!(sh.hyperlinks.is_empty() && sh.comments.is_empty());
 }
+
+#[test]
+fn formulatext_does_not_reveal_a_hidden_formula() {
+    let mut s = s();
+    s.execute("cell.set", json!({"cell": "A1", "input": "=1+1"})).unwrap();
+    s.execute("home.formatCells", json!({"range": "A1", "style": {"protection": {"locked": false, "hidden": true}}})).unwrap();
+    s.execute("home.formatCells", json!({"range": "B1", "style": {"protection": {"locked": false}}})).unwrap();
+    s.execute("cell.set", json!({"cell": "B1", "input": "=FORMULATEXT(A1)"})).unwrap();
+    assert_eq!(v(&s, "B1"), Value::from("=1+1"), "not protected yet");
+    s.execute("review.protectSheet", json!({})).unwrap();
+    s.execute("cell.set", json!({"cell": "B1", "input": "=FORMULATEXT(A1)"})).unwrap();
+    assert_eq!(v(&s, "B1"), Value::Error(gridcraft_core::CellError::NA));
+}
diff --git a/crates/ui-egui/src/app/editing.rs b/crates/ui-egui/src/app/editing.rs
index 8682a435c..a5ac8a176 100644
--- a/crates/ui-egui/src/app/editing.rs
+++ b/crates/ui-egui/src/app/editing.rs
@@ -50,6 +50,11 @@ impl SheetApp {
             self.session.mode = gridcraft_engine::Mode::Edit;
             return;
         }
+        // A hidden formula's source isn't loaded into an edit (a blank edit would also write over
+        // it on commit): no edit starts. Typing still replaces the cell.
+        if text.is_none() && gridcraft_engine::display::formula_hidden(&d.wb, sh, at) {
+            return;
+        }
         let locale = self.ui.language.formula_locale();
         let current = if sh.cell_pictures.contains_key(&at) {
             String::new()