Unparseable code is generated, because ɔ (\u{596}) is not a possible start for a token.

Right now, we do not test if UTF-8 characters are actually valid characters in identifiers, but always assume they are:

• unicode-ident (used by syn and proc-macro2, so we already transitively depend on it) or
• unicode-xid (used by rust's lexer, so we can be sure that its output cannot be wrong, but it is slower, and would pull in more data).

Fuzzing failure in derive (crash-6ae39f08ef6a67885629f22599c93da39eb05bab)

Artifact:

data:application/octet-steam;base64,w/8vLy56ezp7e3t7e3sne3sqKirWltKyeNKSeH19dmFsdWVzdEUqKnRFKgAAAAAXRSoAAAAAAAAAV3N0cnVjdHhyAJI/nnqM0phva2EAAAAmywo=

Formatted test case:

#[test]
fn test() -> Result<(), syn::Error> {
    let input = quote! {
        #[template(
            ext = "//.z{:{{{{",
            source = "{'{{***\u{596}ҲxҒx}}valuestE**tE*\0\0\0\0\u{17}E*\0\0\0\0\0\0\0Wstructxr\0"
        )]
        struct ka {}
    };
    let output = crate::derive_template(input, import_askama);
    let _: syn::File = syn::parse2(output)?;
    Ok(())
}

fn import_askama() -> TokenStream {
    quote! {
        extern crate askama;
    }
}