Function get_cast

src/sql/src/plan/typeconv.rs:1115–1155

Get casts directly between two [`SqlScalarType`]s, with control over the allowed [`CastContext`]. Returns `Err` when the cast is not supported: either no cast exists ([`CastError::InvalidCast`]) or the cast is disallowed ([`CastError::UnsupportedRangeElementType`], e.g. range over float/uint).

(
    ecx: &ExprContext,
    ccx: CastContext,
    from: &SqlScalarType,
    to: &SqlScalarType,
)

/// ([`CastError::InvalidCast`]) or the cast is disallowed
/// ([`CastError::UnsupportedRangeElementType`], e.g. range over float/uint).
fn get_cast(
    ecx: &ExprContext,
    ccx: CastContext,
    from: &SqlScalarType,
    to: &SqlScalarType,
) -> Result<Cast, CastError> {
    use CastContext::*;

    if from == to || (ccx == Implicit && from.base_eq(to)) {
        return Ok(Box::new(|expr| expr));
    }

    // Reject casts to range types with unsupported element types at plan time.
    if let SqlScalarType::Range { element_type } = to {
        validate_range_element_type(ecx, element_type)?;
    }

    let imp = match VALID_CASTS.get(&(from.into(), to.into())) {
        Some(imp) => imp,
        None => {
            return Err(CastError::InvalidCast {
                ccx,
                from: ecx.humanize_sql_scalar_type(from, false),
                to: ecx.humanize_sql_scalar_type(to, false),
            });
        }
    };
    let template = if ccx >= imp.context {
        Some(&imp.template)
    } else {
        None
    };
    match template.and_then(|template| (template.0)(ecx, ccx, from, to)) {
        Some(cast) => Ok(cast),
        None => Err(CastError::InvalidCast {
            ccx,
            from: ecx.humanize_sql_scalar_type(from, false),
            to: ecx.humanize_sql_scalar_type(to, false),
        }),
    }
}

/// Converts an expression to `SqlScalarType::String`.
///