add portable nonnull macros (ros2#382)

* add portable nonnull macros

Signed-off-by: William Woodall <william@osrfoundation.org>

* undo spurious change

Signed-off-by: William Woodall <william@osrfoundation.org>

* uncrustify

Signed-off-by: William Woodall <william@osrfoundation.org>

Signed-off-by: William Woodall <william@osrfoundation.org>

Author: wjwwood

include/rcutils/macros.h

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-/// \file
+/// @file
 
 #ifndef RCUTILS__MACROS_H_
 #define RCUTILS__MACROS_H_
@@ -30,7 +30,7 @@ extern "C"
 #define RCUTILS_WARN_UNUSED _Check_return_
 #endif
 
-/// @cond Doxygen_Suppress
+/// \cond Doxygen_Suppress
 // This block either sets RCUTILS_THREAD_LOCAL or RCUTILS_THREAD_LOCAL_PTHREAD.
 #if defined _WIN32 || defined __CYGWIN__
 // Windows or Cygwin
@@ -142,6 +142,19 @@ extern "C"
 # define RCUTILS_UNLIKELY(x) (x)
 #endif  // _WIN32
 
+// Provide the compiler a hint about an argument being nonnull when possible.
+#ifndef _WIN32
+# define RCUTILS_NONNULL __attribute__((__nonnull__))
+# define RCUTILS_NONNULL_ARGS(...) __attribute__((__nonnull__(__VA_ARGS__)))
+# define RCUTILS_RETURNS_NONNULL __attribute__((__returns_nonnull__))
+# define RCUTILS_HAS_NONNULL 1
+#else
+# define RCUTILS_NONNULL
+# define RCUTILS_NONNULL_ARGS(...)
+# define RCUTILS_RETURNS_NONNULL
+# define RCUTILS_HAS_NONNULL 0
+#endif  // _WIN32
+
 #if defined RCUTILS_ENABLE_FAULT_INJECTION
 #include "rcutils/testing/fault_injection.h"