Re: Reject invalid values for parse.lac in C++ skeleton lalr1.cc

[Akim Demaille]

Hi Adrian,

> Le 19 janv. 2020 à 19:41, Adrian Vogelsgesang <address@hidden> a écrit :
> 
> Hi,
> 
> As reported by Hans Åberg in 
> https://lists.gnu.org/archive/html/bug-bison/2020-01/msg00021.html, the C++ 
> skeleton lalr1.cc accepted arbitrary values for parse.lac.

Yes.  Too bad it was caught after the release of 3.5.1, I would have wanted it
to be part of it.

> The attached patch makes sure we only accept the two values “none” and “full” 
> and reject all other values. You can also find this patch on 
> https://github.com/akimd/bison/pull/23

Great!

> I am not completely convinced this patch is the right solution, though.
> Although not intentionally, version 3.5.0 and 3.5.1 accepted “-Dparse.lac” to 
> enable LAC-support. With this patch, “-Dparse.lac” is rejected again and 
> “-Dparse.lac=full” has to be used instead. Personally, I think we can live 
> with this breaking behavior, In particular given that “-Dparse.lac” was never 
> documented and I would prefer to keep the set of supported parameters as 
> small as possible.
> What do you think?

I would have asked myself exactly the same questions, reaching the same
conclusion.  I'll wrap 3.5.2 with this patch in a week or two, just in
case something else pops up.  Maybe I'll be done with the CI under Windows,
and more tweaks might be needed.

Thanks for the prompt reaction.

A few minor issues:

> Just as the yacc.c skeleton, the lalr1.cc skeleton should reject
> reject invalid value for parse.lac.

Too many "rejects", and I guess "values".


+AT_BISON_CHECK([[-Dparse.lac=none input.y]], [[0]], [], [])
+AT_BISON_CHECK([[-Dparse.lac=none -L c++ input.y]], [[0]], [], [])
+AT_BISON_CHECK([[-Dparse.lac=full input.y]], [[0]], [], [])
+AT_BISON_CHECK([[-Dparse.lac=full -L c++ input.y]], [[0]], [], [])

Rely on the default values here, pass only the first argument.

Cheers!