[libvirt PATCH] meson: avoid bogus warnings from clang and g_autoptr

[Daniel P. Berrangé]

Clang has previously had trouble with G_DEFINE_AUTOPTR_CLEANUP_FUNC
generated code, thinking it was unused. We turn off -Wunused-function
to avoid tripping up on that with CLang.

New CLang has started having trouble with g_autoptr now too. In usage
scenarios where the variable is set, but never again read, it thinks
it is unused not realizing the destructor has useful side effects.
For this we have to skip -Wunused-but-set-variable on CLang.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 meson.build | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/meson.build b/meson.build
index 5af09d319a..dbd70b6483 100644
--- a/meson.build
+++ b/meson.build
@@ -470,6 +470,26 @@ if get_option('warning_level') == '2'
     supported_cc_flags += [ '-Wno-unused-function' ]
   endif
 
+  # Clang complains about unused variables in many scenarios arelated
+  # to attribute((cleanup)) aka g_auto*
+  w_unused_but_set_var_args = [ '-Wunused-but-set-variable', '-Werror' ]
+  w_unused_but_set_var_code = '''
+    static inline void free_pointer (void *p) {
+      void **pp = (void**)p;
+      free (*pp);
+    }
+
+    int main(void) {
+      __attribute__((cleanup(free_pointer))) char *buffer = 0x0;
+      buffer = 0x1;
+    }
+  '''
+  # We previously turned on unused-but-set-variable, so we must turn
+  # it off again explicitly now.
+  if not cc.compiles(w_unused_but_set_var_code, args: w_unused_but_set_var_args)
+    supported_cc_flags += [ '-Wno-unused-but-set-variable' ]
+  endif
+
 endif
 add_project_arguments(supported_cc_flags, language: 'c')
 
-- 
2.31.1