error: no rules expected the token `$`
  --> $DIR/best-failure.rs:4:30
   |
LL | macro_rules! number {
   | ------------------- when calling this macro
...
LL |         number!(neg $signed, $self);
   |                              ^^^^^ no rules expected this token in macro call
...
LL | number! { false => u8; }
   | ------------------------ in this macro invocation
   |
note: while trying to match meta-variable `$self:ident`
  --> $DIR/best-failure.rs:2:17
   |
LL |     (neg false, $self:ident) => { $self };
   |                 ^^^^^^^^^^^
   = note: this error originates in the macro `number` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error