macros: simplify tt matchers (original) (raw)

Ideally, tt matches either a single token or delimited sequence (e.g. { arbitrary tokens }).
However, the following compiles today:

macro_rules! m { ($t:tt) => {} } m!($x); m!($(x)*); m!($x:ident);

We want to avoid leaking details of macro_rules! syntax into the semantics of tt, at least for macros 2.0.