Method determine_key

src/sql/src/func.rs:1463–1524

Attempt to resolve all polymorphic types to a single "key" type. For `target_for_param_type` to be useful, this must have already been called.

(&mut self, ecx: &ExprContext)

    /// `target_for_param_type` to be useful, this must have already been
    /// called.
    fn determine_key(&mut self, ecx: &ExprContext) -> bool {
        self.key = if !self.seen.iter().any(|v| v.is_coerced()) {
            match &self.compat {
                // No encountered param was polymorphic
                None => None,
                // Params were polymorphic, but we never received a known type.
                // This cannot be delegated to `guess_best_common_type`, which
                // will incorrectly guess string, which is incompatible with
                // `BestCommonList`, `BestCommonMap`.
                Some(t) => match t {
                    PolymorphicCompatClass::BestCommonAny => Some(SqlScalarType::String),
                    PolymorphicCompatClass::BestCommonList => Some(SqlScalarType::List {
                        custom_id: None,
                        element_type: Box::new(SqlScalarType::String),
                    }),
                    PolymorphicCompatClass::BestCommonMap => Some(SqlScalarType::Map {
                        value_type: Box::new(SqlScalarType::String),
                        custom_id: None,
                    }),
                    // Do not infer type.
                    PolymorphicCompatClass::StructuralEq | PolymorphicCompatClass::Any => None,
                },
            }
        } else {
            // If we saw any polymorphic parameters, we must have determined the
            // compatibility type.
            let compat = self.compat.as_ref().unwrap();

            let r = match compat {
                PolymorphicCompatClass::Any => {
                    let mut s = self
                        .seen
                        .iter()
                        .filter_map(|f| f.as_coerced().cloned())
                        .collect::<Vec<_>>();
                    let (candiate, remaining) =
                        s.split_first().expect("have at least one non-None element");
                    if remaining.iter().all(|r| r.base_eq(candiate)) {
                        s.remove(0)
                    } else {
                        return false;
                    }
                }
                _ => match typeconv::guess_best_common_type(ecx, &self.seen) {
                    Ok(r) => r,
                    Err(_) => return false,
                },
            };

            // Ensure the best common type is compatible.
            for t in self.seen.iter() {
                if let CoercibleScalarType::Coerced(t) = t {
                    if !compat.compatible(ecx, t, &r) {
                        return false;
                    }
                }
            }
            Some(r)