Re: [PATCH nft v2] parser_bison: on syntax errors, output expected tokens

["Jan Kończak" <jan.konczak@cs.put.poznan.pl>]

> Or am I missing some detail about YYBISON?

No, I don't think you're missing any detail there. I considered this
less intrusive than forcing a define in the configure.ac. Adding a C
macro BISON_CUSTOM_ERROR from configure is actually more versatile.


I just discovered that while autotools forbid conditional AM_YFLAGS,
they allow conditional YACC. It's counterintuitive to me why.
Yet, the following works in Makefile.am:

| if BISON_CUSTOM_ERROR
| YACC += -D parse.error=custom -D parse.lac=full
| AM_CFLAGS += -DBISON_CUSTOM_ERROR
| else
| YACC += -D parse.error=verbose
| endif

Then, the configure.ac has just to set the BISON_CUSTOM_ERROR, without
putting there the flags/define which nobody expects to be there.
To me this looks cleaner.


I guess adding a AC_ARG_ENABLE on that might be worthwhile, too.
Running "nft --debug parser ..." with parse.lac=full yields extra
output which one may or may not prefer if one wishes to debug
parser_bison.y. I mean, something akin to this:

| AC_ARG_ENABLE([custom_parser_errors],
|        AS_HELP_STRING(
|                [--disable-custom-parser-errors],
|                [Disable use of parse.error=custom and LAC in Bison]
|        ),[
|                # keeping the user choice for custom-parser-errors
|        ],[
|                enable_custom_parser_errors=no
|                AC_SUBST([BISON],[$ac_cv_prog_YACC])
|                AX_PROG_BISON_VERSION([3.6],
|                    [enable_custom_parser_errors=yes])
|        ]
| )
| AM_CONDITIONAL([BISON_CUSTOM_ERROR],
|                [test "x$enable_custom_parser_errors" != xno])


Regards, Jan