bug#15594: trunk r114639: * lisp/progmodes/ruby-mode.el (ruby-smie-grammar): Add rule for paren-free

[Stefan Monnier]

>> Calling ruby-smie--forward-token is a bit dangerous since that function
>> might itself be called from ruby-smie--forward-token.  It might work,
>> but you'll have to think hard about why an inf-loop is not possible.
> Hopefully because both `ruby-smie--forward-token' and
> ruby-smie--backward-token' would only call `ruby-smie--forward-token', and
> only when (> pos (point)), IOW there has to be some whitespace skipping done
> between the recursive calls.

Only recursing in one direction (only forward or only backward) is
a good way to guarantee progress, indeed.  But currently
ruby-smie--implicit-semi-p calls ruby-smie--backward-token, so beware.


        Stefan