Function sql_impl

src/sql/src/func.rs:346–401

Backing implementation for sql_impl_func and sql_impl_cast. See those functions for details.

(
    expr: &str,
)

/// Backing implementation for sql_impl_func and sql_impl_cast. See those
/// functions for details.
pub fn sql_impl(
    expr: &str,
) -> impl Fn(&ExprContext, Vec<SqlScalarType>) -> Result<HirScalarExpr, PlanError> + use<> {
    let expr = mz_sql_parser::parser::parse_expr(expr).unwrap_or_else(|e| {
        panic!(
            "static function definition failed to parse {}: {}",
            expr.quoted(),
            e,
        )
    });
    move |ecx, types| {
        // Reconstruct an expression context where the parameter types are
        // bound to the types of the expressions in `args`.
        let mut scx = ecx.qcx.scx.clone();
        scx.param_types = RefCell::new(
            types
                .into_iter()
                .enumerate()
                .map(|(i, ty)| (i + 1, ty))
                .collect(),
        );
        let qcx = QueryContext::root(&scx, ecx.qcx.lifetime);

        let (mut expr, new_ids) = names::resolve(qcx.scx.catalog, expr.clone())?;
        scx.sql_impl_resolved_ids
            .lock()
            .expect("planning is single-threaded")
            .extend_from(&new_ids);
        // Desugar the expression
        transform_ast::transform(&scx, &mut expr)?;

        let ecx_name = format!(
            "static function definition (or its outer context '{}')",
            ecx.name
        );
        let ecx = ExprContext {
            qcx: &qcx,
            name: ecx_name.as_str(),
            scope: &Scope::empty(),
            relation_type: &SqlRelationType::empty(),
            // Constrain the new context by the outer context's `allow_subqueries`.
            // (We could potentially to the same for `allow_aggregates` and `allow_windows`, I just
            // don't want to think these through until we have a concrete use case.)
            // (`allow_parameters` we have to set true, because that is the machinery for function
            // arguments, i.e., parameters from in here won't escape `sql_impl_func` or
            // `sql_impl_cast`.)
            allow_aggregates: false,
            allow_subqueries: ecx.allow_subqueries,
            allow_parameters: true,
            allow_windows: false,
        };

        // Plan the expression.
        query::plan_expr(&ecx, &expr)?.type_as_any(&ecx)
    }
}

// Constructs a definition for a built-in function out of a static SQL