# added --enable-gcc-warnings (not for user consumption).

configure.in

@@ -16,6 +16,29 @@ AM_PROG_CC_STDC
 AC_PROG_INSTALL
 AC_PROG_RANLIB
 
+AC_ARG_ENABLE(gcc-warnings,
+[  --enable-gcc-warnings   turn on lots of GCC warnings (not recommended)],
+[case "${enableval}" in
+   yes|no) ;;
+   *)      AC_MSG_ERROR([bad value ${enableval} for gcc-warnings option]) ;;
+ esac
+],
+enableval=no
+)
+if test "${enableval}" = yes; then
+  BISON_WARNING(-Wall)
+  BISON_WARNING(-W)
+  BISON_WARNING(-Wbad-function-cast)
+  BISON_WARNING(-Wcast-align)
+  BISON_WARNING(-Wcast-qual)
+  BISON_WARNING(-Wmissing-declarations)
+  BISON_WARNING(-Wmissing-prototypes)
+  BISON_WARNING(-Wnested-externs)
+  BISON_WARNING(-Wno-char-subscripts)
+  BISON_WARNING(-Wstrict-prototypes)
+  BISON_WARNING(-Wwrite-strings)
+fi
+
 dnl Checks for libraries.
 
 dnl Checks for header files.

m4/warning.m4

@@ -0,0 +1,11 @@
+AC_DEFUN(BISON_WARNING,
+[AC_MSG_CHECKING(whether compiler accepts $1)
+AC_SUBST(WARNING_CFLAGS)
+ac_save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS $1"
+AC_TRY_COMPILE(,
+[int x;],
+WARNING_CFLAGS="$WARNING_CFLAGS $1"
+AC_MSG_RESULT(yes),
+AC_MSG_RESULT(no))
+CFLAGS="$ac_save_CFLAGS"])

src/Makefile.am

@@ -5,7 +5,7 @@ DEFS = @DEFS@ \
   -DXPFILE=\"${datadir}/bison.simple\" \
   -DXPFILE1=\"${datadir}/bison.hairy\" \
   -DLOCALEDIR=\"${datadir}/locale\"
-INCLUDES = -I../intl -I$(top_srcdir)/intl -I..
+INCLUDES = -I../intl -I$(top_srcdir)/intl -I.. $(WARNING_CFLAGS)
 LDADD = @INTLLIBS@ ../lib/libbison.a
 
 bin_PROGRAMS = bison