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

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

> conditional setting of AM_YFLAGS variable in Makefile.am is problematic
> (...)
> what I tried was:
> |   AM_YFLAGS = -d -Wno-yacc
> |  
> |  +if BISON_CUSTOM_ERROR
> |  +AM_YFLAGS += …

Any conditional change in Makefile.am I came up with is put aside by
autotools. The lines "AM_YFLAGS += ..." end up in a ".PRECIOUS" target
in the resulting Makefile and are never applied before bison is called.

I guess moving the %define's from parser_bison.y to bison command line
arguments, and a '#if YYBISON >= 30704' that disables the error
reporting code is a way to go, one only must subdue the autotools.
The YYBISON macro generated by bison has the version encoded starting
from 3.7.4, hence that particular version.

My (working) take on that would be as follows, though I can tell that
mangling the options in configure.ac is a shitty workaround. I never
really wrote autotools configs myself, and I don't have a clue how to
do it better. Feel free to include any part of it in case it helps.

Regards, Jan

====================================================================
diff --git a/configure.ac b/configure.ac
index 0d3ee2ac..9b61cd38 100644
--- a/configure.ac
+++ b/configure.ac
@@ -45,6 +45,13 @@ then
         exit 1
 fi
 
+AC_PATH_PROG([BISON],[bison])
+AX_PROG_BISON_VERSION([3.7.4],[
+	AC_SUBST([YACC], [$(echo "$ac_cv_prog_YACC -D parse.error=custom -D parse.lac=full")])
+],[
+	AC_SUBST([YACC], [$(echo "$ac_cv_prog_YACC -D parse.error=verbose")])
+])
+
 AM_PROG_AR
 LT_INIT([disable-static])
 AC_EXEEXT
diff --git a/src/parser_bison.y b/src/parser_bison.y
index 5a334bf0..25b875ec 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -221,8 +221,14 @@ int nft_lex(void *, void *, void *);
 %parse-param		{ void *scanner }
 %parse-param		{ struct parser_state *state }
 %lex-param		{ scanner }
-%define parse.error custom
-%define parse.lac full
+// Note: configure.ac controls the following defines:
+// if bison version is 3.7.4 or newer:
+//   %define parse.lac full
+//   %define parse.error custom
+// else
+//   %define parse.error verbose
+// Notice that bison 3.6 introduces parse.error custom, but starting from
+// 3.7.4 a numeric macro enablkes checking version
 %locations
 
 %initial-action {
@@ -6537,6 +6543,7 @@ exthdr_key		:	HBH	close_scope_hbh	{ $$ = IPPROTO_HOPOPTS; }
 
 %%
 
+#if YYBISON >= 30704
 static int
 yyreport_syntax_error(const yypcontext_t *yyctx, struct nft_ctx *nft,
                       void *scanner, struct parser_state *state)
@@ -6592,3 +6599,4 @@ yyreport_syntax_error(const yypcontext_t *yyctx, struct nft_ctx *nft,
 	free(msg);
 	return 0;
 }
+#endif