`ruint-macro/src/lib`: BLOCKED) Replace with Diagnostic API when stable.

[github-actions[bot]]

On 2022-05-28 @recmo wrote in 1ec2e50 “Recognize new tags”:

BLOCKED) Replace with Diagnostic API when stable. See https://doc.rust-lang.org/stable/proc_macro/struct.Diagnostic.html

    );
    TokenStream::from_str(&source).unwrap()
}

/// Construct a compiler error message.
// FEATURE: (BLOCKED) Replace with Diagnostic API when stable.
// See <https://doc.rust-lang.org/stable/proc_macro/struct.Diagnostic.html>
fn error(span: Span, message: &str) -> TokenStream {
    // See: https://docs.rs/syn/1.0.70/src/syn/error.rs.html#243
    TokenStream::from_iter(vec![
        TokenTree::Ident(Ident::new("compile_error", span)),
        TokenTree::Punct({

From ruint-macro/src/lib.rs:24