Edit: text that would parse as a number or formula keeps its quote prefix in the editor (#1362)

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

ROADMAP.md

@@ -21,6 +21,7 @@ This page is the summary. The detail is in:
 
 | Number | Value | Kind |
 |---|---|---|
+| 2026-10-14 | Editing a cell with text that would read back as a number, boolean, date or formula (entered with a leading apostrophe) shows the apostrophe in the editor and formula bar, so Enter unchanged keeps it text (#1362) |
 | **Feature breadth** (weighted) | **~75%** | estimated, anchored on two measurements: ribbon catalog 274 / 290 (94.5%), worksheet functions 513 / 523 (98.1%; 504 working, 96.4%) |
 | **Ready for real work** | **~50%** | estimated from written weights (51.6); [target-app-parity.md](docs/target-app-parity.md) |
 | **Mainstream practitioner** | **~50%** | estimated: typical analyst/finance user, weekly features, × 0.90 interaction × 0.92 stability × 0.88 file exchange; [method](docs/target-app-parity.md#mainstream-practitioner) |

crates/engine/src/display.rs

@@ -33,6 +33,25 @@ pub fn format(v: &Value, code: &str, wb: &Workbook) -> Formatted {
     format_value(v, &parsed(code), wb.date_system)
 }
 
+/// Whether typing `t` back into a General cell would not give the text `t` again (it would parse
+/// as a number, boolean, error, date or formula, or lose a leading apostrophe). Such text is shown
+/// for editing with a leading `'`, as Excel does for text carrying a quote prefix, so that
+/// committing the editor unchanged keeps the cell as text.
+fn text_needs_quote_prefix(t: &str, sys: gridcraft_core::date::DateSystem) -> bool {
+    if t.is_empty() {
+        return false;
+    }
+    let mut chars = t.chars();
+    let (first, second) = (chars.next(), chars.next());
+    if matches!(first, Some('=' | '\'')) {
+        return true;
+    }
+    if matches!(first, Some('+' | '-')) && second.is_some_and(|c| c.is_ascii_alphabetic() || c == '(') {
+        return true;
+    }
+    !matches!(gridcraft_core::parse::parse_input(t, sys).value, Value::Text(ref x) if x.as_ref() == t)
+}
+
 /// What the cell editor and the formula bar start from. Same as `Cell::input_text`, except that a
 /// constant number in a date or time format is shown as a date (as the grid shows it), not as its
 /// serial. When the formatted text would not read back as the same date (for example
@@ -41,6 +60,13 @@ pub fn format(v: &Value, code: &str, wb: &Workbook) -> Formatted {
 pub fn edit_text(wb: &Workbook, sheet: &Sheet, c: CellRef) -> String {
     let raw = sheet.input_text(c);
     let Some(cell) = sheet.cell(c) else { return raw };
+    if let Value::Text(t) = &cell.value
+        && cell.formula.is_none()
+        && wb.styles.get(cell.style).num_fmt.as_str() != "@"
+        && text_needs_quote_prefix(t, wb.date_system)
+    {
+        return format!("'{raw}");
+    }
     let Value::Number(n) = &cell.value else { return raw };
     let code = wb.styles.get(cell.style).num_fmt.as_str();
     if cell.formula.is_some() || !parsed(code).is_date() {

crates/engine/src/tests.rs

@@ -3282,3 +3282,26 @@ fn paste_special_validation_moves_relative_references() {
     assert!(!ok(&mut s, "C3", "5"), "the pasted rule checks C3, not A1");
     assert!(ok(&mut s, "C3", "20"));
 }
+
+#[test]
+fn editing_quote_prefixed_text_keeps_it_text() {
+    let mut s = s();
+    for (i, input) in ["'00123", "'=1+1", "'TRUE", "''abc"].iter().enumerate() {
+        let cell = format!("A{}", i + 1);
+        s.execute("cell.set", json!({"cell": cell, "input": input})).unwrap();
+        let at = CellRef::parse(&cell).unwrap();
+        let before = v(&s, &cell);
+        let edit = {
+            let d = s.doc().unwrap();
+            crate::display::edit_text(&d.wb, d.wb.active().unwrap(), at)
+        };
+        assert_eq!(&edit, input, "edit text of {cell}");
+        // Committing the editor unchanged leaves the cell as it was.
+        s.execute("cell.set", json!({"cell": cell, "input": edit})).unwrap();
+        assert_eq!(v(&s, &cell), before, "{cell}");
+    }
+    // Plain text is shown as typed, without a prefix.
+    s.execute("cell.set", json!({"cell": "B1", "input": "hello"})).unwrap();
+    let d = s.doc().unwrap();
+    assert_eq!(crate::display::edit_text(&d.wb, d.wb.active().unwrap(), CellRef::parse("B1").unwrap()), "hello");
+}