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Follow token checking is too restrictive. #21545
Description
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?
Activity
vadimcn commentedon Jan 23, 2015
cc @cmr
emberian commentedon Jan 23, 2015
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 commentedon Jan 24, 2015
Created PR to amend the RFC.
steveklabnik commentedon Feb 2, 2016
Traige: the RFC was pursued, so closing this.