util: Do not expose fallthrough defines

Use meson to detect if the compiler supports the fallthrough attribute
and if so just add corresponding define to the private config.h.

This avoid leaking the fallthrough define outside of the projects
which can cause consuming projects to fail to compile.

Signed-off-by: Daniel Wagner <[email protected]>

Author: dwsuse

meson.build

@@ -186,6 +186,29 @@ conf.set10(
     description: 'Is linux/mctp.h include-able?'
 )
 
+if meson.version().version_compare('>= 0.48')
+  has_fallthrough = cc.has_function_attribute('fallthrough')
+else
+  has_fallthrough = cc.compiles(
+    '''int main(int argc, char **argv) {
+           switch(argc) {
+               case 0:
+                   __attribute__((__fallthrough__));
+               case 1:
+                   return 1;
+           }
+           return 0;
+       }
+    ''',
+    name: 'has fallthrough')
+endif
+
+if has_fallthrough
+  conf.set('fallthrough', '__attribute__((__fallthrough__))')
+else
+  conf.set('fallthrough', 'do {} while (0) /* fallthrough */')
+endif
+
 ################################################################################
 substs = configuration_data()
 substs.set('NAME',    meson.project_name())

src/nvme/util.h

@@ -17,12 +17,6 @@
  * libnvme utility functions
  */
 
-#if __has_attribute(__fallthrough__)
-# define fallthrough __attribute__((__fallthrough__))
-#else
-# define fallthrough do {} while (0) /* fallthrough */
-#endif
-
 /**
  * enum nvme_connect_err - nvme connect error codes
  * @ENVME_CONNECT_RESOLVE:	failed to resolve host