[Libguestfs] [PATCH] build: build mlaugeas with -Wno-shift-negative-value

[Pino Toscano]

The embedded copy of ocaml-augeas does Val_int(-1), which in turns
triggers warnings in newer GCC versions about "left shift of negative
value".  The issue actually lies in the OCaml headers (mlvalues.h in
particular), and it was fixed in newer OCaml versions.

Since the code is actually correct, disable -Wshift-negative-value with
-Wno-shift-negative-value (checking whether the compiler has it).
---
 common/mlaugeas/Makefile.am | 2 +-
 m4/guestfs-c.m4             | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/common/mlaugeas/Makefile.am b/common/mlaugeas/Makefile.am
index d71d0074d..0f3cea820 100644
--- a/common/mlaugeas/Makefile.am
+++ b/common/mlaugeas/Makefile.am
@@ -53,7 +53,7 @@ libmlaugeas_a_CPPFLAGS = \
 	-I$(top_builddir) \
 	-I$(shell $(OCAMLC) -where)
 libmlaugeas_a_CFLAGS = \
-	$(WARN_CFLAGS) $(WERROR_CFLAGS) \
+	$(WARN_CFLAGS) $(NO_SNV_CFLAGS) $(WERROR_CFLAGS) \
 	$(LIBVIRT_CFLAGS) $(LIBXML2_CFLAGS) \
 	-fPIC
 
diff --git a/m4/guestfs-c.m4 b/m4/guestfs-c.m4
index 6621a2747..13310d5db 100644
--- a/m4/guestfs-c.m4
+++ b/m4/guestfs-c.m4
@@ -105,6 +105,12 @@ gl_WARN_ADD([-Wformat-truncation=1])
 
 AC_SUBST([WARN_CFLAGS])
 
+NO_SNV_CFLAGS=
+gl_COMPILER_OPTION_IF([-Wno-shift-negative-value],[
+    NO_SNV_CFLAGS="-Wno-shift-negative-value"
+])
+AC_SUBST([NO_SNV_CFLAGS])
+
 AC_DEFINE([lint], [1], [Define to 1 if the compiler is checking for lint.])
 AC_DEFINE([GNULIB_PORTCHECK], [1], [Enable some gnulib portability checks.])
 AH_VERBATIM([FORTIFY_SOURCE],[
-- 
2.13.6