Function find_match

src/sql/src/func.rs:1084–1295

Finds an exact match based on the arguments, or, if no exact match, finds the best match available. Patterned after [PostgreSQL's type conversion matching algorithm][pgparser]. [pgparser]: https://www.postgresql.org/docs/current/typeconv-func.html

(
    ecx: &ExprContext,
    types: &[CoercibleScalarType],
    impls: Vec<&'a FuncImpl<R>>,
)

///
/// [pgparser]: https://www.postgresql.org/docs/current/typeconv-func.html
fn find_match<'a, R: std::fmt::Debug>(
    ecx: &ExprContext,
    types: &[CoercibleScalarType],
    impls: Vec<&'a FuncImpl<R>>,
) -> Result<&'a FuncImpl<R>, usize> {
    let all_types_known = types.iter().all(|t| t.is_coerced());

    // Check for exact match.
    if all_types_known {
        let known_types: Vec<_> = types.iter().filter_map(|t| t.as_coerced()).collect();
        let matching_impls: Vec<&FuncImpl<_>> = impls
            .iter()
            .filter(|i| i.params.exact_match(&known_types))
            .cloned()
            .collect();

        if matching_impls.len() == 1 {
            return Ok(matching_impls[0]);
        }
    }

    // No exact match. Apply PostgreSQL's best match algorithm. Generate
    // candidates by assessing their compatibility with each implementation's
    // parameters.
    let mut candidates: Vec<Candidate<_>> = Vec::new();
    macro_rules! maybe_get_last_candidate {
        () => {
            if candidates.len() == 1 {
                return Ok(&candidates[0].fimpl);
            }
        };
    }
    let mut max_exact_matches = 0;

    for fimpl in impls {
        let mut exact_matches = 0;
        let mut preferred_types = 0;
        let mut near_matches = 0;

        for (i, arg_type) in types.iter().enumerate() {
            let param_type = &fimpl.params[i];

            match arg_type {
                CoercibleScalarType::Coerced(arg_type) => {
                    if param_type == arg_type {
                        exact_matches += 1;
                    }
                    if param_type.is_preferred_by(arg_type) {
                        preferred_types += 1;
                    }
                    if param_type.is_near_match(arg_type) {
                        near_matches += 1;
                    }
                }
                CoercibleScalarType::Record(_) | CoercibleScalarType::Uncoerced => {
                    if param_type.prefers_self() {
                        preferred_types += 1;
                    }