Function build_method_precondition_checks 

pub(crate) fn build_method_precondition_checks(
    inputs: &Punctuated<FnArg, Comma>,
    per_param: &HashMap<String, ParamAttrs>,
    coerce_all: bool,
) -> Vec<String>

Build R-side precondition stopifnot() lines for a parameter list, given its match_arg/choices per-param map and whether coerce is active for the whole method.

Neither impl methods nor trait methods carry a per-param coerce flag (only function-wide coerce, see ParsedMethod::per_param docs), so coerce_params is always empty here. Shared by MethodContext::precondition_checks and TraitMethodContext::precondition_checks.