Function normalize_r_arg_string 

pub fn normalize_r_arg_string(name: &str) -> String

Normalizes a Rust argument name (its crate::naming::ident_name, no r#) for R.

• Leading _ → stripped (Rust convention for unused params)
• Leading __ → stripped
• Otherwise → unchanged

Examples

• _x → x
• _to → to
• __field → field
• value → value

Note: We strip underscores rather than prefixing “unused” because R callers (like vctrs) may use named arguments that must match the original name.

This is the R formal of a parameter without a declared formal = ".." only: R-facing names come from Formals::of, which applies it.