Follow token checking is too restrictive.

[vadimcn]

macro_rules! foo {
    ( $x:ident $(: $y:ident )* ) => ( $x $(: $y )* )
}

<anon>:2:16: 2:30 error: `$x:ident` is followed by a sequence repetition, which is not allowed for `ident` fragments
<anon>:2     ( $x:ident $(: $y:ident )* ) => ( $x $(: $y )* )

The RFC says that ident may be followed by any token, so why repetition of any tokens would be invalid?

[vadimcn]

cc @cmr

[emberian]

The follow sets are only for real tokens, not complex NTs. To extend this properly, the algorithm will need to compute the FIRST of the following token to ensure that it is a subset of the FOLLOW set for that token.

[vadimcn]

Created PR to amend the RFC.

[steveklabnik]

Traige: the RFC was pursued, so closing this.