Function build_generic_subs

src/inheritance.rs:1298–1358

Build a substitution map from a class's template parameters and concrete type arguments. Handles right-alignment when fewer arguments than template parameters are provided (see [`apply_generic_args`] for details on the heuristic). Returns an empty map when no substitutions can be made (e.g. when `template_params` or `type_args` is empty).

(
    class: &ClassInfo,
    type_args: &[PhpType],
)

/// Returns an empty map when no substitutions can be made (e.g. when
/// `template_params` or `type_args` is empty).
pub(crate) fn build_generic_subs(
    class: &ClassInfo,
    type_args: &[PhpType],
) -> HashMap<String, PhpType> {
    if class.template_params.is_empty() || type_args.is_empty() {
        return HashMap::new();
    }

    // When fewer type arguments are provided than template parameters,
    // right-align the args so that trailing (value) params get bound
    // and leading key-like params stay unbound.  This handles the
    // common PHP pattern of writing `Collection<Model>` instead of
    // `Collection<int, Model>` — the single arg should bind to
    // `TValue`/`TModel`, not `TKey`.
    //
    // The heuristic only activates when every skipped leading param
    // has an `array-key` (or `int` / `string`) bound, which is the
    // universal convention for collection key parameters.
    let offset = if type_args.len() < class.template_params.len() {
        let skip = class.template_params.len() - type_args.len();
        let all_skipped_are_key_like = class.template_params[..skip].iter().all(|param| {
            class
                .template_param_bounds
                .get(param)
                .is_some_and(is_key_like_bound)
        });
        if all_skipped_are_key_like { skip } else { 0 }
    } else {
        0
    };

    let mut subs = HashMap::new();
    for (i, param_name) in class.template_params.iter().enumerate() {
        if i < offset {
            // Skipped (right-aligned) params: fall back to their
            // declared upper bound or `mixed` so the raw template
            // name never leaks into downstream consumers.
            let fallback = class
                .template_param_bounds
                .get(param_name)
                .cloned()
                .unwrap_or_else(PhpType::mixed);
            subs.insert(param_name.to_string(), fallback);
            continue;
        }
        if let Some(arg) = type_args.get(i - offset) {
            subs.insert(param_name.to_string(), arg.clone());
        } else {
            // Unbound param (more template params than type args and
            // right-alignment didn't apply): use upper bound or `mixed`.
            let fallback = class
                .template_param_bounds
                .get(param_name)
                .cloned()
                .unwrap_or_else(PhpType::mixed);
            subs.insert(param_name.to_string(), fallback);
        }
    }