[PULL v2 01/25] osdep: add 'ignore_value(x)' macro

[Stefan Hajnoczi <stefanha@xxxxxxxxxx>]

From: Daniel P. Berrangé <berrange@xxxxxxxxxx>

Functions annotated with 'warn_unused_result' cannot be cast
to (void) to silence the compiler. Add the ignore_value()
macro which tricks the compiler into thinking the result is
genuinely used, avoiding the need for manual workarounds where
the return value is intentionally ignored.

This clever macro is derived from one originating with the
GNULIB project:

  
https://gitweb.git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=lib/ignore-value.h;hb=HEAD

but simplified since we don't need compat with old GCC and
optimizing on clang is overkill.

Reviewed-by: Eric Blake <eblake@xxxxxxxxxx>
Reviewed-by: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
Message-id: 20261102142844.3464712-2-berrange@xxxxxxxxxx
Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
 include/qemu/osdep.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 50c7ce33b6a..b27d159d5bb 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -251,6 +251,14 @@ extern "C" {
 #endif
 
 
+/*
+ * Merely casting to (void) is not sufficient for functions
+ * annotated with the "warn_unused_result" attribute
+ */
+#define ignore_value(x) \
+    (__extension__ ({ __typeof__(x) __x = (x); (void) __x; }))
+
+
 /*
  * For mingw, as of v6.0.0, the function implementing the assert macro is
  * not marked as noreturn, so the compiler cannot delete code following an
-- 
2.56.0