Re: [nft PATCH v2] parser_bison: Fix for bison < 3.6

Hey Phil,

I see a configure failure after this change [1] on ubuntu-24.04.

  ./configure: line 5247: syntax error near unexpected token `3.6,'
  ./configure: line 5247: `			AX_PROG_BISON_VERSION(3.6,'
  Error: Process completed with exit code 2.

Does ax_prog_bison_version.m4 need to be added to the m4 directory?

Thanks.
E.

[1]: https://github.com/firewalld/firewalld/actions/runs/30020547439/job/89969654992

On Thu, Jul 23, 2026 at 12:09:14PM +0200, Phil Sutter wrote:
> On Thu, Jun 11, 2026 at 02:52:25PM +0200, Phil Sutter wrote:
> > Support for 'custom' parse.error value was added in bison-3.6. Fall back
> > to previous value for earlier versions.
> > 
> > This is harder to get right than it seems: On one hand, preprocessor
> > macros can't be used in parser_bison.y's declaration section and
> > automake forbids conditional changes to AM_YFLAGS on the other.
> > 
> > Another aspect complicating things is compiling with (an up to date)
> > parser_bison.c in place vs. without: Dist tarballs generally have it in
> > place, relieving users from having to provide a YACC when compiling. The
> > existing parser_bison.c either uses parse.error=custom or not which does
> > not (should not) change when compiling. Hiding yyreport_syntax_error()
> > behind a CPPFLAG which may be set or not depending on bison presence and
> > version then causes trouble if it doesn't match how parser_bison.c was
> > created.
> > 
> > Avoid these pitfalls by:
> > - Not relying upon a preprocessor define to control parser_bison.c
> >   compilation, instead check existence of the bison-internal
> >   YY_LAC_ESTABLISH macro
> > - Exporting the above macro existence check in a variable for use by
> >   main.c (thereby crossing the libnftables library boundary)
> > 
> > Also:
> > - Introduce have_prebuilt_bison variable in configure.ac, unifying the
> >   parser_bison.c existence check and solidify the latter by also
> >   comparing its timestamp
> > - Report extended parser errors enableval in configure only if
> >   parser_bison.c will be recreated, otherwise we can't quite tell if it
> >   will turn out to be enabled or not
> > 
> > Suggested-by: Jan Kończak <[email protected]>
> > Fixes: 67b822f2b2624 ("parser_bison: on syntax errors, output expected tokens")
> > Signed-off-by: Phil Sutter <[email protected]>
> 
> Patch applied.
>