eval/refops

/// An operand of a reference operator: its reference, or the error value that is the result.
fn reference(operand: &CalcValue) -> Result<&ReferenceLike, CalcValue> {
    match operand.core_ref() {
        CoreRef::Reference(reference) => Ok(reference),
        CoreRef::Error(_) if operand.callable_value().is_none() => Err(operand.clone()),
        _ => Err(CalcValue::error(WorksheetErrorCode::Value)),
    }
}

/// The references of `operands`, all on one sheet, or the value that is the result.
fn references(operands: &[CalcValue]) -> Result<Vec<&ReferenceLike>, CalcValue> {
    let mut out = Vec::with_capacity(operands.len());
    for operand in operands {
        out.push(reference(operand)?);
    }
    let sheet = out[0].sheet();
    // A 3-D reference meets none of the operators (Excel 16.0, 2026-10-23:
    // `=SUM(Ja:Ma!A1:A2 Ja:Ma!A1)` is #VALUE!).
    if out
        .iter()
        .any(|reference| reference.sheet() != sheet || reference.spans_sheets())
    {
        return Err(CalcValue::error(WorksheetErrorCode::Value));
    }
    Ok(out)
}

fn bounds(area: GridArea) -> (u32, u32, u32, u32) {
    (
        area.first().row(),
        area.first().column(),
        area.last().row(),
        area.last().column(),
    )
}

/// The area of `like`'s sheet between the given rows and columns, which lie on the grid.
fn area(like: GridArea, top: u32, left: u32, bottom: u32, right: u32) -> GridArea {
    let sheet = like.sheet();
    GridArea::new(
        CellKey::new(sheet, top, left).expect("a corner of areas on the grid"),
        CellKey::new(sheet, bottom, right).expect("a corner of areas on the grid"),
    )
    .expect("both corners lie on one sheet")
}