Function plan_function_order_by

src/sql/src/plan/query.rs:5176–5193

Plans the ORDER BY clause of a window function. Unfortunately, we have to create two HIR structs from an AST OrderByExpr: A ColumnOrder has asc/desc and nulls first/last, but can't represent an HirScalarExpr, just a column reference by index. Therefore, we return both HirScalarExprs and ColumnOrders. Note that the column references in the ColumnOrders point NOT to input columns, but into the `Vec

(
    ecx: &ExprContext,
    order_by: &[OrderByExpr<Aug>],
)

/// Note that the column references in the ColumnOrders point NOT to input columns, but into the
/// `Vec<HirScalarExpr>` that we return.
fn plan_function_order_by(
    ecx: &ExprContext,
    order_by: &[OrderByExpr<Aug>],
) -> Result<(Vec<HirScalarExpr>, Vec<ColumnOrder>), PlanError> {
    let mut order_by_exprs = vec![];
    let mut col_orders = vec![];
    {
        for (i, obe) in order_by.iter().enumerate() {
            // Unlike `SELECT ... ORDER BY` clauses, function `ORDER BY` clauses
            // do not support ordinal references in PostgreSQL. So we use
            // `plan_expr` directly rather than `plan_order_by_or_distinct_expr`.
            let expr = plan_expr(ecx, &obe.expr)?.type_as_any(ecx)?;
            order_by_exprs.push(expr);
            col_orders.push(resolve_desc_and_nulls_last(obe, i));
        }
    }
    Ok((order_by_exprs, col_orders))
}

/// Returns a human-readable rendering of `name`, falling back to a debug
/// dump of the `ResolvedItemName` if humanization fails. Used to construct