Function postprocess_singletons 

pub fn postprocess_singletons(
    tokens: TokenStream,
    resolved_exprs: impl IntoIterator<Item = TokenStream>,
) -> Punctuated<Expr, Comma>

Replaces singleton references with the code needed to actually get the value inside.

• tokens - The tokens to update singleton references within.
• resolved_exprs - Token streams that correspond 1:1 and in the same order as the singleton references within tokens (found in-order via preprocess_singletons).

For shared refs: splices the resolved expression directly (e.g. &T or &Option<T>). For mutable refs: splices the resolved expression directly (e.g. &mut T or &mut Option<T>).