Model: an input name that reads as a cell reference is refused

A macro could declare an input called Q1, AB12 or Sum1, and a step written
with plain A1 text, as a recorded one is, would then resolve to the input's
range instead of the cell. check_limits refuses such names; the docs say so.
Regression test.

crates/engine/src/macros/tests.rs

@@ -149,6 +149,20 @@ fn a_visible_name_that_looks_like_macro_storage_is_left_alone() {
     assert_eq!(wb.names, vec![name]);
 }
 
+#[test]
+fn input_names_that_read_as_cell_references_are_refused() {
+    // A recorded step holds plain A1 text; an input called `Q1` would take its place.
+    let with_input = |name: &str| json!({"name": "M", "inputs": [{"name": name}]});
+    for name in ["Q1", "AB12", "Sum1", "a1"] {
+        let err = parse_macro(&with_input(name)).unwrap_err();
+        assert!(err.contains("reads as a cell reference"), "{name}: {err}");
+    }
+    for name in ["Amount", "Q", "Sales_Q1", "Total1a"] {
+        assert!(parse_macro(&with_input(name)).is_ok(), "{name}");
+    }
+    assert!(parse_macro(&with_input("Row")).unwrap_err().contains("token of its own"));
+}
+
 #[test]
 fn a_hidden_macro_name_this_build_did_not_write_is_kept() {
     // `_gc_macro_index_0` is not a numbered item: it is neither read nor dropped on open, and a

crates/model/src/macros.rs

@@ -113,6 +113,10 @@ impl Macro {
             if ["Output", "Row", "Column", "Name"].iter().any(|r| r.eq_ignore_ascii_case(n)) {
                 return Err(format!("'{n}' is a token of its own and can't name an input."));
             }
+            // A step written with plain A1 text (a recorded one) must keep meaning the cell.
+            if gridcraft_core::RangeRef::parse(n).is_some() {
+                return Err(format!("'{n}' reads as a cell reference and can't name an input."));
+            }
             if self.inputs.iter().take(k).any(|o| o.name.eq_ignore_ascii_case(n)) {
                 return Err(format!("Two inputs are called '{n}'."));
             }

docs/macros.md

@@ -39,7 +39,10 @@ version.
 - **Inputs**: `kind` (`cell` or `range`), `rows` and `cols` as `[min, max]` (0 for no maximum;
   rows exclude the header), `header`, `colTypes` (`number`, `text`, `date`, `bool`, `any`),
   `nonEmpty` and `defaultRef`. These declare what a range must look like for the macro to work
-  on it. This version stores and checks the declaration; it does not bind inputs or run macros.
+  on it. An input's name is letters, digits and `_`, starting with a letter, and is neither a
+  token of its own (`Output`, `Row`, `Column`, `Name`) nor something that reads as a cell
+  reference (`Q1`), so a step written with plain A1 text keeps meaning the cell. This version
+  stores and checks the declaration; it does not bind inputs or run macros.
 - **Limits**: 1,000 macros a workbook, 10,000 steps a macro, and Repeat and If nested 4 deep.
 
 ## Storage