darwin-lib/warn-on-use.h

#ifndef _GL_WARN_ON_USE

# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
/* A compiler attribute is available in gcc versions 4.3.0 and later.  */
#  define _GL_WARN_ON_USE(function, message) \
extern __typeof__ (function) function __attribute__ ((__warning__ (message)))
# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
/* Verify the existence of the function.  */
#  define _GL_WARN_ON_USE(function, message) \
extern __typeof__ (function) function
# else /* Unsupported.  */
#  define _GL_WARN_ON_USE(function, message) \
_GL_WARN_EXTERN_C int _gl_warn_on_use
# endif
#endif

/* _GL_WARN_ON_USE_CXX (function, rettype, parameters_and_attributes, "string")
   is like _GL_WARN_ON_USE (function, "string"), except that the function is
   declared with the given prototype, consisting of return type, parameters,
   and attributes.
   This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does
   not work in this case.  */
#ifndef _GL_WARN_ON_USE_CXX
# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
#  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
extern rettype function parameters_and_attributes \
     __attribute__ ((__warning__ (msg)))
# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
/* Verify the existence of the function.  */
#  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
extern rettype function parameters_and_attributes
# else /* Unsupported.  */
#  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
_GL_WARN_EXTERN_C int _gl_warn_on_use
# endif
#endif

/* _GL_WARN_EXTERN_C declaration;
   performs the declaration with C linkage.  */
#ifndef _GL_WARN_EXTERN_C
# if defined __cplusplus
#  define _GL_WARN_EXTERN_C extern "C"
# else
#  define _GL_WARN_EXTERN_C extern
# endif
#endif