Function validate_self_ref_count

nodedb-sql/src/planner/cte.rs:260–307

Validate that the CTE name appears exactly once in the recursive arm and not inside a subquery, aggregate function, or the nullable side of an outer join. Returns `Ok(())` if the reference is valid, or a typed error otherwise.

(expr: &SetExpr, cte_name: &str)

///
/// Returns `Ok(())` if the reference is valid, or a typed error otherwise.
fn validate_self_ref_count(expr: &SetExpr, cte_name: &str) -> Result<()> {
    let select = match expr {
        SetExpr::Select(s) => s,
        // Non-SELECT arm: no self-ref needed.
        _ => return Ok(()),
    };

    let mut count = 0usize;

    for from in &select.from {
        if table_ref_matches(&from.relation, cte_name) {
            count += 1;
        }
        for join in &from.joins {
            if table_ref_matches(&join.relation, cte_name) {
                // Reject self-ref on the nullable side of an outer join.
                if is_nullable_join_side(&join.join_operator) {
                    return Err(SqlError::InvalidRecursiveSelfRef {
                        cte_name: cte_name.to_owned(),
                        reason: "self-reference on the nullable side of an outer join is not \
                                 permitted; use INNER JOIN or move the CTE reference to the \
                                 driving table position"
                            .into(),
                    });
                }
                count += 1;
            }
        }
    }

    // Subquery self-references are not permitted.
    if where_contains_subquery_ref(&select.selection, cte_name) {
        return Err(SqlError::InvalidRecursiveSelfRef {
            cte_name: cte_name.to_owned(),
            reason: "self-reference inside a subquery is not permitted".into(),
        });
    }

    if count > 1 {
        return Err(SqlError::InvalidRecursiveSelfRef {
            cte_name: cte_name.to_owned(),
            reason: format!("self-reference appears {count} times; exactly one is required"),
        });
    }

    // count == 0 is fine for the value-generating case (no table ref at all).
    Ok(())
}

fn table_ref_matches(factor: &ast::TableFactor, cte_name: &str) -> bool {
    match factor {