AC_DEFUN([_NM_COMPILER_FLAG], [

	CFLAGS_SAVED="$CFLAGS"

	CFLAGS="$CFLAGS $GLIB_CFLAGS -Werror $1"

	AC_MSG_CHECKING([whether $1 works as expected])

	AC_COMPILE_IFELSE([AC_LANG_SOURCE([[]])], [

		AC_COMPILE_IFELSE([AC_LANG_SOURCE([[$2]])], [

			AC_MSG_RESULT(yes)

			CFLAGS="$CFLAGS_SAVED"

			$3

		],[

			AC_MSG_RESULT(no)

			CFLAGS="$CFLAGS_SAVED"

			$4

		])

	],[

		AC_MSG_RESULT(not supported)

		CFLAGS="$CFLAGS_SAVED"

	])

])

dnl Check whether a particular compiler flag is supported,

dnl append it to the specified variable if the check succeeds.

dnl NM_COMPILER_FLAG([ENV-VAR], [FLAG], [ACTION-IF-SUPPORTED], [ACTION-IF-NOT-SUPPORTED])

AC_DEFUN([NM_COMPILER_FLAG], [

        _NM_COMPILER_FLAG([$2], [], [

		eval "AS_TR_SH([$1])='$$1 $2'"

		$3

	], [$4])

])

dnl Check whether a particular warning is not emitted with code provided,

dnl append an option to disable the warning to a specified variable if the check fails.

dnl NM_COMPILER_WARNING([ENV-VAR], [C-SNIPPET], [WARNING]])

AC_DEFUN([NM_COMPILER_WARNING], [

        _NM_COMPILER_FLAG([-W$2], [$3], [eval "AS_TR_SH([$1])='$$1 -W$2'"], [eval "AS_TR_SH([$1])='$$1 -Wno-$2'"])

])

dnl NM_COMPILER_WARNINGS([ENV-VAR], [MORE-WARNINGS])

AC_DEFUN([NM_COMPILER_WARNINGS],

[AC_ARG_ENABLE(more-warnings,

	AS_HELP_STRING([--enable-more-warnings], [Possible values: no/yes/error]),

	set_more_warnings="$enableval",set_more_warnings=$2)

AC_MSG_CHECKING(for more warnings)

if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then

	AC_MSG_RESULT(yes)

	dnl This is enabled in clang by default, makes little sense,

	dnl and causes the build to abort with -Werror.

	CFLAGS_SAVED="$$1"

	eval "AS_TR_SH([$1])='$$1 -Qunused-arguments'"

	AC_COMPILE_IFELSE([AC_LANG_SOURCE([])], [], eval "AS_TR_SH([$1])='$CFLAGS_SAVED'")

	unset CFLAGS_SAVED

	dnl clang only warns about unknown warnings, unless

	dnl called with "-Werror=unknown-warning-option"

	dnl Test if the compiler supports that, and if it does

	dnl attach it to the CFLAGS.

	NM_COMPILER_WARNING([$1], [unknown-warning-option], [])

	CFLAGS_MORE_WARNINGS="-Wall"

	if test "x$set_more_warnings" = xerror; then

		CFLAGS_MORE_WARNINGS="$CFLAGS_MORE_WARNINGS -Werror"

	fi

	for option in \

		      -Wextra \

		      -Wdeclaration-after-statement \

		      -Wfloat-equal \

		      -Wformat-nonliteral \

		      -Wformat-security \

		      -Wimplicit-fallthrough \

		      -Wimplicit-function-declaration \

		      -Winit-self \

		      -Wlogical-op \

		      -Wmissing-declarations \

		      -Wmissing-include-dirs \

		      -Wmissing-prototypes \

		      -Wpointer-arith \

		      -Wshadow \

		      -Wshift-negative-value \

		      -Wstrict-prototypes \

		      -Wundef \

		      -Wvla \

		      -Wno-duplicate-decl-specifier \

		      -Wno-format-truncation \

		      -Wno-format-y2k \

		      -Wno-missing-field-initializers \

		      -Wno-pragmas \

		      -Wno-sign-compare \

		      -Wno-unused-parameter \

		      ; do

		dnl GCC 4.4 does not warn when checking for -Wno-* flags (https://gcc.gnu.org/wiki/FAQ#wnowarning)

		_NM_COMPILER_FLAG([-Wall $(printf '%s' "$option" | sed 's/^-Wno-/-W/')], [],

		                  [CFLAGS_MORE_WARNINGS="$CFLAGS_MORE_WARNINGS $option"], [])

	done

	unset option

	dnl Disable warnings triggered by known compiler problems

	dnl https://bugzilla.gnome.org/show_bug.cgi?id=745821

	NM_COMPILER_WARNING([$1], [unknown-attributes], [#include <glib.h>])

	dnl https://bugzilla.gnome.org/show_bug.cgi?id=744473

	NM_COMPILER_WARNING([$1], [typedef-redefinition], [#include <gio/gio.h>])

	dnl https://llvm.org/bugs/show_bug.cgi?id=21614

	NM_COMPILER_WARNING([$1], [array-bounds],

		[#include <string.h>]

		[void f () { strcmp ("something", "0"); }]

	)

	dnl https://llvm.org/bugs/show_bug.cgi?id=22949

	NM_COMPILER_WARNING([$1], [parentheses-equality],

		[#include <sys/wait.h>]

		[void f () { if (WIFCONTINUED(0)) return; }]

	)

	dnl systemd-dhcp's log_internal macro and our handle_warn are sometimes

	dnl used in void context,u sometimes in int. Makes clang unhappy.

	NM_COMPILER_WARNING([$1], [unused-value],

		[#define yolo ({ (666 + 666); })]

		[int f () { int i = yolo; yolo; return i; }]

	)

	dnl clang 3.9 would like to see "{ { 0 } }" here, but that does not

	dnl look too wise.

	NM_COMPILER_WARNING([$1], [missing-braces],

		[union { int a[1]; int b[2]; } c = { 0 }]

	)

	dnl a new warning in gcc 8, glib 2.55 doesn't play nice yet

	dnl https://bugzilla.gnome.org/show_bug.cgi?id=793272

	NM_COMPILER_WARNING([$1], [cast-function-type],

		[#include <glib-object.h>]

		[typedef struct { GObject parent; } NMObject;]

		[typedef struct { GObjectClass parent; } NMObjectClass;]

		[static void nm_object_init (NMObject *object) { } ]

		[static void nm_object_class_init (NMObjectClass *object) { }]

		[G_DEFINE_TYPE (NMObject, nm_object, G_TYPE_OBJECT)]

	)

	eval "AS_TR_SH([$1])='$CFLAGS_MORE_WARNINGS $$1'"

else

	AC_MSG_RESULT(no)

fi

])

AC_DEFUN([NM_LTO],

[AC_ARG_ENABLE(lto, AS_HELP_STRING([--enable-lto], [Enable Link Time Optimization for smaller size (default: no)]))

if (test "${enable_lto}" = "yes"); then

	CC_CHECK_FLAG_APPEND([lto_flags], [CFLAGS], [-flto])

	if (test -n "${lto_flags}"); then

		CFLAGS="-flto $CFLAGS"

	else

		AC_MSG_ERROR([Link Time Optimization -flto is not supported.])

	fi

else

	enable_lto='no'

fi

])

AC_DEFUN([NM_LD_GC],

[AC_ARG_ENABLE(ld-gc, AS_HELP_STRING([--enable-ld-gc], [Enable garbage collection of unused symbols on linking (default: auto)]))

if (test "${enable_ld_gc}" != "no"); then

	CC_CHECK_FLAG_APPEND([ld_gc_flags], [CFLAGS], [-fdata-sections -ffunction-sections -Wl,--gc-sections])

	if (test -n "${ld_gc_flags}"); then

		enable_ld_gc="yes"

		CFLAGS="$ld_gc_flags $CFLAGS"

	else

		if (test "${enable_ld_gc}" = "yes"); then

			AC_MSG_ERROR([Unused symbol eviction requested but not supported.])

		else

			enable_ld_gc="no"

		fi

	fi

fi

])