warning: the following explicit lifetimes could be elided: 'a
      --> src/rcvec.rs:96:6
       |
    96 | impl<'a, T> RcVecMut<'a, T> {
       |      ^^              ^^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes
       = note: `-W clippy::needless-lifetimes` implied by `-W clippy::all`
       = help: to override `-W clippy::all` add `#[allow(clippy::needless_lifetimes)]`
    help: elide the lifetimes
       |
    96 - impl<'a, T> RcVecMut<'a, T> {
    96 + impl<T> RcVecMut<'_, T> {
       |

    warning: docs for function which may panic missing `# Panics` section
       --> src/lib.rs:836:5
        |
    836 |     pub fn new(ch: char, spacing: Spacing) -> Self {
        |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
    note: first possible panic found here
       --> src/lib.rs:846:13
        |
    846 |             panic!("unsupported proc macro punctuation character {:?}", ch);
        |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_panics_doc
        = note: `-W clippy::missing-panics-doc` implied by `-W clippy::pedantic`
        = help: to override `-W clippy::pedantic` add `#[allow(clippy::missing_panics_doc)]`

Valid punctuation characters generated by:

    use proc_macro::{Punct, Spacing, TokenStream};
    use std::panic;

    #[proc_macro]
    pub fn punct_chars(_input: TokenStream) -> TokenStream {
        for ch in '\0'..=char::MAX {
            if let Ok(_) = panic::catch_unwind(|| {
                let _ = Punct::new(ch, Spacing::Alone);
            }) {
                eprintln!("{:?}", ch);
            }
        }
        TokenStream::new()
    }

Check valid punctuation character in Punct::new