I wrote:
Bison 2.2 also has a new feature:
: * %require "VERSION" : This specifies that the grammar file depends on features implemented : in Bison version VERSION or higher.
Since we actively use some newer (2.0 and/or 2.1) features of Bison, we actually should use this check, to avoid users even trying with older Bisons which cannot work. OTOH, since the check is new in 2.2, we can't "%require 2.1", so by using this check we would needlessly (ATM) require Bison 2.2.
What should we do? Perhaps wait until 2.2 is more widespread, then require it?
Of course, there's also this bug in previous Bisons, leading to a parser crash the Chief observed, that Waldek fixed for 2.2. This would suggest to upgrade to Bison 2.2 sooner rather than later. Still, by adding a "%require" directive, we would force users to upgrade (only those who actually rebuild the Bison file at all, though, i.e. not for a normal GPC build).
Frank