Always check -Wno-unused-but-set-variable gcc support

[zfs.git] / config / always-no-unused-but-set-variable.m4

diff --git a/config/always-no-unused-but-set-variable.m4 b/config/always-no-unused-but-set-variable.m4
new file mode 100644 (file)
index 0000000..0e2634d
--- /dev/null
+++ b/config/always-no-unused-but-set-variable.m4
@@ -0,0 +1,27 @@
+dnl #
+dnl # Check if gcc supports -Wno-unused-but-set-variable option.
+dnl #
+dnl # We actually invoke gcc with the -Wunused-but-set-variable option
+dnl # and infer the 'no-' version does or doesn't exist based upon
+dnl # the results.  This is required because when checking any of
+dnl # no- prefixed options gcc always returns success.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_NO_UNUSED_BUT_SET_VARIABLE], [
+       AC_MSG_CHECKING([for -Wno-unused-but-set-variable support])
+
+       saved_flags="$CFLAGS"
+       CFLAGS="$CFLAGS -Wunused-but-set-variable"
+
+       AC_RUN_IFELSE(AC_LANG_PROGRAM( [], []),
+       [
+               NO_UNUSED_BUT_SET_VARIABLE=-Wno-unused-but-set-variable
+               AC_MSG_RESULT([yes])
+       ],
+       [
+               NO_UNUSED_BUT_SET_VARIABLE=
+               AC_MSG_RESULT([no])
+       ])
+
+       CFLAGS="$saved_flags"
+       AC_SUBST([NO_UNUSED_BUT_SET_VARIABLE])
+])