Re: Bison 3.6 requires runtime type information?

[Akim Demaille]

Hi Adrian,

> Le 27 juin 2020 à 10:21, Adrian <withoutpointk@gmail.com> a écrit :
> 
> Hi,
> 
> The exact error message I'm getting is:
> 
> In constructor 'Parser::semantic_type::semantic_type(T&&)’:
> error: cannot use typeid with -fno-rtti

So your skeleton is lalr1.cc (variants are not supported by glr.cc).

> I'm just specifying %language "c++".
> What's the difference between using that declaration and using the
> skeleton declaration?

From the language and directives such as %glr-parser, a skeleton is
chosen.

> Should I be doing both (but everything seemed to work fine with C++
> and bison 3.4.2 without the skeleton declaration)?

No, what you did is fine.

> I'm not sure exactly what command I'm running as I'm using the cmake module.
> But I would guess the only flags it passes are for setting the output files.
> 
> When I grep the bison 3.6.4 source for "typeid", I find references
> inside data/skeletons/variant.hh.
> Indeed, I am using variants along with api.token.constructor.
> However, strangely when I grep the 3.4.2 source, I also find
> references to typeid (in that same file),
> so I'm not sure why I'm only getting a compilation error now.
> 
> Hopefully this provides more useful information.
> Please let me know if I can provide anything else.

We don't _need_ rtti, we just use it when Bison's assertions are
enabled, via

%define parse.assert

in which case you should not pass -fno-rtti to the compiler, indeed.

I'll add the commit below to the documentation.  Note that I don't
think anything changed on this regard since 3.4, the problem might be
elsewhere.

Cheers!


commit 4efb2f7bd27d496e2aacb8867b53f7d22d8dfeda
Author: Akim Demaille <akim.demaille@gmail.com>
Date:   Sat Jun 27 10:31:59 2020 +0200

    doc: parse.assert in C++ requires RTTI
    
    * doc/bison.texi (%define Summary): Say it.

diff --git a/doc/bison.texi b/doc/bison.texi
index ac71fe6d..41461d29 100644
--- a/doc/bison.texi
+++ b/doc/bison.texi
@@ -6658,7 +6658,10 @@ In C, some important invariants in the implementation of 
the parser are
 checked when this option is enabled.
 
 In C++, when variants are used (@pxref{C++ Variants}), symbols must be
-constructed and destroyed properly.  This option checks these constraints.
+constructed and destroyed properly.  This option checks these constraints
+using runtime type information (RTTI).  Therefore the generated code cannot
+be compiled with RTTI disabled (via compiler options such as
+@option{-fno-rtti}).
 
 @item Accepted Values: Boolean