From 7ffc0a6534fb66ad27d22984e25bd0789f4404b6 Mon Sep 17 00:00:00 2001
From: Jan Maria Matejka <mq@ucw.cz>
Date: Tue, 14 Aug 2018 14:36:44 +0200
Subject: [PATCH] Bison: A bit more verbose error messages in config.

---
 Makefile.in   | 1 +
 aclocal.m4    | 2 ++
 conf/Makefile | 2 +-
 configure.ac  | 5 +++++
 4 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Makefile.in b/Makefile.in
index 6e281cfc..b755df44 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -10,6 +10,7 @@ CPPFLAGS=-I$(objdir) -I$(srcdir) @CPPFLAGS@
 CFLAGS=$(CPPFLAGS) @CFLAGS@
 LDFLAGS=@LDFLAGS@
 M4FLAGS=@M4FLAGS@
+BISONFLAGS=@BISONFLAGS@
 LIBS=@LIBS@
 DAEMON_LIBS=@DAEMON_LIBS@
 CLIENT_LIBS=@CLIENT_LIBS@
diff --git a/aclocal.m4 b/aclocal.m4
index 28a632c8..c401d447 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -185,9 +185,11 @@ AC_DEFUN([BIRD_CHECK_BISON_VERSION],
       ;;
     2.*)
       bird_bison_synclines=no
+      bird_bison_enhanced_error=no
       ;;
     3.* | 4.* | 5.* | 6.* | 7.* | 8.* | 9.*)
       bird_bison_synclines=yes
+      bird_bison_enhanced_error=yes
       ;;
     *)
       AC_MSG_ERROR([Couldn't parse Bison version $$1. Call the developers for help.])
diff --git a/conf/Makefile b/conf/Makefile
index 47024d26..39628bff 100644
--- a/conf/Makefile
+++ b/conf/Makefile
@@ -20,7 +20,7 @@ $(o)commands.h: | $(s)gen_commands.m4 $(srcdir)/client/cmds.m4
 $(o)cf-parse.tab.h: $(o)cf-parse.tab.c
 
 $(o)cf-parse.tab.c: $(o)cf-parse.y
-	$(BISON) $(BISON_DEBUG) -dv -pcf_ -b $(@:.tab.c=) $<
+	$(BISON) $(BISON_DEBUG) $(BISONFLAGS) -dv -pcf_ -b $(@:.tab.c=) $<
 
 $(o)cf-lex.c: $(s)cf-lex.l
 	$(FLEX) $(FLEX_DEBUG) -s -B -8 -Pcf_ -o$@ $<
diff --git a/configure.ac b/configure.ac
index 9a2e55e2..943d3a7b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -164,7 +164,12 @@ if test "$bird_bison_synclines" = yes; then
   M4FLAGS="$M4FLAGS -s"
 fi
 
+if test "$bird_bison_enhanced_error" = yes; then
+  BISONFLAGS="$BISONFLAGS -Dparse.lac=full -Dparse.error=verbose"
+fi
+
 AC_SUBST([M4FLAGS])
+AC_SUBST([BISONFLAGS])
 
 BIRD_CHECK_PROG_FLAVOR_GNU([$M4],
   [],