Function peeled_inputs 

pub(crate) fn peeled_inputs(
    inputs: &Punctuated<FnArg, Comma>,
    markers: &[(String, Vec<ParamMarker>)],
) -> Result<Punctuated<FnArg, Comma>>

inputs with each marked parameter’s type replaced by the type under its markers (markers, keyed by Rust name): what every R-side consumer and the conversion see. The item re-emitted for the user keeps the markers.