Function param_key 

pub(crate) fn param_key(rust_name: &str) -> String

The {r_param} part of a parameter’s placeholders: its Rust name (rust_name, crate::naming::ident_name) without leading underscores, also when it declares an R formal (#1842). The placeholders are replaced before R reads the text, and placeholder_ident_suffix makes Rust identifiers of them, so a declared formal, which may hold a ., never becomes part of one.