From c929feb416d9936267830cb05d801a1ec34193be Mon Sep 17 00:00:00 2001
From: Sebastian Harl <sh@tokkee.org>
Date: Thu, 4 Dec 2014 17:35:45 +0100
Subject: [PATCH] Bootstrap the build system for C++ as well.

That is, check CXX support for strict compiler flags.

Also, use all configured strict flags when checking for other strict flags.
This way, we detect problems when using flags that are not supported in C++
mode.
---
 configure.ac    | 63 ++++++++++++++++++++++++++++++++++++++++++-------
 src/Makefile.am |  1 +
 2 files changed, 55 insertions(+), 9 deletions(-)

diff --git a/configure.ac b/configure.ac
index e395d5f..10c18c9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,6 +44,7 @@ AC_LANG(C)
 AC_SYS_LARGEFILE
 
 AC_PROG_CC
+AC_PROG_CXX
 AC_PROG_CPP
 AC_PROG_INSTALL
 AC_PROG_LN_S
@@ -72,14 +73,25 @@ m4_ifdef([LT_INIT],
 )
 
 test_cc_flags() {
-	AC_LANG_CONFTEST([AC_LANG_PROGRAM([[ ]], [[ ]])])
-	$CC -c conftest.c $CFLAGS $@ > /dev/null 2> /dev/null
+	AC_LANG_CONFTEST([int main(void){}])
+	$CC -c conftest.c $CFLAGS $STRICT_CFLAGS $@ > /dev/null 2> /dev/null
 	ret=$?
 	rm -f conftest.o
 	return $ret
 }
 
+test_cxx_flags() {
+	AC_LANG_PUSH(C++)
+	AC_LANG_CONFTEST([int main(void){}])
+	$CXX -c conftest.c $CXXFLAGS $STRICT_CXXFLAGS $@ > /dev/null 2> /dev/null
+	ret=$?
+	rm -f conftest.o
+	AC_LANG_POP(C++)
+	return $ret
+}
+
 STRICT_CFLAGS=""
+STRICT_CXXFLAGS=""
 
 m4_divert_once([HELP_ENABLE], [
 Build options:])
@@ -130,23 +142,37 @@ AC_ARG_ENABLE([hardening],
 		[enable_hardening="yes"])
 
 if test "x$enable_hardening" = "xyes"; then
-	hardening=0
+	hardening_cc=0
+	hardening_cxx=0
 	hardening_tests=0
 	for flag in -Wformat -Wformat-security; do
 		hardening_tests=$(($hardening_tests + 1))
-		AC_MSG_CHECKING([whether $CC accepts $flag])
 
+		AC_MSG_CHECKING([whether $CC accepts $flag])
 		if test_cc_flags $flag; then
 			STRICT_CFLAGS="$STRICT_CFLAGS $flag"
-			hardening=$(($hardening + 1))
+			hardening_cc=$(($hardening_cc + 1))
+			AC_MSG_RESULT([yes])
+		else
+			AC_MSG_RESULT([no])
+		fi
+
+		AC_MSG_CHECKING([whether $CXX accepts $flag])
+		if test_cxx_flags $flag; then
+			STRICT_CXXFLAGS="$STRICT_CXXFLAGS $flag"
+			hardening_cxx=$(($hardening_cxx + 1))
 			AC_MSG_RESULT([yes])
 		else
 			AC_MSG_RESULT([no])
 		fi
 	done
-	if test $hardening -ne $hardening_tests; then
+	if test $hardening_cc -ne $hardening_tests; then
 		AC_MSG_WARN(
-				[Some hardening options are not supported by your compiler!])
+				[Some hardening options are not supported by your C compiler!])
+	fi
+	if test $hardening_cxx -ne $hardening_tests; then
+		AC_MSG_WARN(
+				[Some hardening options are not supported by your C++ compiler!])
 	fi
 fi
 
@@ -159,13 +185,20 @@ AC_ARG_ENABLE([strict-checks],
 
 for flag in -Wall -Werror; do
 	AC_MSG_CHECKING([whether $CC accepts $flag])
-
 	if test_cc_flags $flag; then
 		STRICT_CFLAGS="$STRICT_CFLAGS $flag"
 		AC_MSG_RESULT([yes])
 	else
 		AC_MSG_RESULT([no])
 	fi
+
+	AC_MSG_CHECKING([whether $CXX accepts $flag])
+	if test_cxx_flags $flag; then
+		STRICT_CXXFLAGS="$STRICT_CXXFLAGS $flag"
+		AC_MSG_RESULT([yes])
+	else
+		AC_MSG_RESULT([no])
+	fi
 done
 
 if test "x$enable_strict_checks" = "xyes"; then
@@ -182,16 +215,28 @@ if test "x$enable_strict_checks" = "xyes"; then
 			-Wshadow \
 			-Wstrict-prototypes; do
 		AC_MSG_CHECKING([whether $CC accepts $flag])
-
 		if test_cc_flags $flag; then
 			STRICT_CFLAGS="$STRICT_CFLAGS $flag"
 			AC_MSG_RESULT([yes])
 		else
 			AC_MSG_RESULT([no])
 		fi
+
+		dnl -Wshadow produces unnecessary warnings/errors in case a
+		dnl C function name "shadows" a struct constructor.
+		if test "x$flag" != "x-Wshadow"; then
+			AC_MSG_CHECKING([whether $CXX accepts $flag])
+			if test_cxx_flags $flag; then
+				STRICT_CXXFLAGS="$STRICT_CXXFLAGS $flag"
+				AC_MSG_RESULT([yes])
+			else
+				AC_MSG_RESULT([no])
+			fi
+		fi
 	done
 fi
 AC_SUBST([STRICT_CFLAGS])
+AC_SUBST([STRICT_CXXFLAGS])
 
 AC_ARG_ENABLE([gcov],
 		AS_HELP_STRING([--enable-gcov],
diff --git a/src/Makefile.am b/src/Makefile.am
index 64b6ec4..1583217 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -2,6 +2,7 @@ SUBDIRS = liboconfig
 
 # coverage related flags are only set when gcov is enabled
 AM_CFLAGS = @STRICT_CFLAGS@ @COVERAGE_CFLAGS@ @PROFILING_CFLAGS@
+AM_CXXFLAGS = @STRICT_CXXFLAGS@ @COVERAGE_CFLAGS@ @PROFILING_CFLAGS@
 AM_LDFLAGS = @COVERAGE_LDFLAGS@ @PROFILING_LDFLAGS@
 AM_CPPFLAGS  = -I"${top_srcdir}/src/include"
 AM_CPPFLAGS += -DSYSCONFDIR='"${sysconfdir}"'
-- 
2.30.2