Re: new module 'c++defs'

[Bruno Haible]

Hi John,

> |   foo.cc: In function ‘int main()’:
> |   foo.cc:21: warning: call to ‘open’ declared with attribute warning: The 
> symbol ::open refers to the system function. Use gnulib::open instead.
> 
> Will this warning happen on all systems when a module is used, or just
> when the replacement function is needed?

It will happen on all systems, assuming g++ is used.

> How does this macro avoid
> causing trouble with things like myclass::open?

It uses the _GL_WARN_ON_USE macro.

> I guess I would 
> have a better understanding if I could see your latest version of the code.

Find the latest c++defs.h attached.

> Are your updated changes available somewhere for testing? 

I'm currently testing them on Linux, MacOS X, Solaris, and will commit them
afterwards.

Bruno


============================= build-aux/c++defs.h =============================
/* C++ compatible function declaration macros.
   Copyright (C) 2010 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published
   by the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#ifndef _GL_CXXDEFS_H
#define _GL_CXXDEFS_H

/* The three most frequent use cases of these macros are:

   * For providing a substitute for a function that is missing on some
     platforms, but is declared and works fine on the platforms on which
     it exists:

       #if @GNULIB_FOO@
       # if address@hidden@
       _GL_FUNCDECL_SYS (foo, ...);
       # endif
       _GL_CXXALIAS_SYS (foo, ...);
       _GL_CXXALIASWARN (foo);
       #elif defined GNULIB_POSIXCHECK
       ...
       #endif

   * For providing a replacement for a function that exists on all platforms,
     but is broken/insufficient and needs to be replaced on some platforms:

       #if @GNULIB_FOO@
       # if @REPLACE_FOO@
       #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
       #   undef foo
       #   define foo rpl_foo
       #  endif
       _GL_FUNCDECL_RPL (foo, ...);
       _GL_CXXALIAS_RPL (foo, ...);
       # else
       _GL_CXXALIAS_SYS (foo, ...);
       # endif
       _GL_CXXALIASWARN (foo);
       #elif defined GNULIB_POSIXCHECK
       ...
       #endif

   * For providing a replacement for a function that exists on some platforms
     but is broken/insufficient and needs to be replaced on some of them and
     is additionally either missing or undeclared on some other platforms:

       #if @GNULIB_FOO@
       # if @REPLACE_FOO@
       #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
       #   undef foo
       #   define foo rpl_foo
       #  endif
       _GL_FUNCDECL_RPL (foo, ...);
       _GL_CXXALIAS_RPL (foo, ...);
       # else
       #  if address@hidden@   or   if address@hidden@ 
       _GL_FUNCDECL_SYS (foo, ...);
       #  endif
       _GL_CXXALIAS_SYS (foo, ...);
       # endif
       _GL_CXXALIASWARN (foo);
       #elif defined GNULIB_POSIXCHECK
       ...
       #endif
*/

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

/* _GL_FUNCDECL_RPL (func, rettype, parameters_and_attributes);
   declares a replacement function, named rpl_func, with the given prototype,
   consisting of return type, parameters, and attributes.
   Example:
     _GL_FUNCDECL_RPL (open, int, (const char *filename, int flags, ...)
                                  _GL_ARG_NONNULL ((1)));
 */
#define _GL_FUNCDECL_RPL(func,rettype,parameters_and_attributes) \
  _GL_FUNCDECL_RPL_1 (rpl_##func, rettype, parameters_and_attributes)
#define _GL_FUNCDECL_RPL_1(rpl_func,rettype,parameters_and_attributes) \
  _GL_EXTERN_C rettype rpl_func parameters_and_attributes

/* _GL_FUNCDECL_SYS (func, rettype, parameters_and_attributes);
   declares the system function, named func, with the given prototype,
   consisting of return type, parameters, and attributes.
   Example:
     _GL_FUNCDECL_SYS (open, int, (const char *filename, int flags, ...)
                                  _GL_ARG_NONNULL ((1)));
 */
#define _GL_FUNCDECL_SYS(func,rettype,parameters_and_attributes) \
  _GL_EXTERN_C rettype func parameters_and_attributes

/* _GL_CXXALIAS_RPL (func, rettype, parameters)
   declares a C++ alias called GNULIB_NAMESPACE::func
   that redirects to rpl_func, if GNULIB_NAMESPACE is defined.
   Example:
     _GL_CXXALIAS_RPL (open, int, (const char *filename, int flags, ...));
 */
#define _GL_CXXALIAS_RPL(func,rettype,parameters) \
  _GL_CXXALIAS_RPL_1 (func, rpl_##func, rettype, parameters)
#if defined __cplusplus && defined GNULIB_NAMESPACE
# define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
    namespace GNULIB_NAMESPACE                                \
    {                                                         \
      rettype (*const func) parameters = ::rpl_func;          \
    }                                                         \
    _GL_EXTERN_C int _gl_cxxalias_dummy
#else
# define _GL_CXXALIAS_RPL_1(func,rpl_func,rettype,parameters) \
    _GL_EXTERN_C int _gl_cxxalias_dummy
#endif

/* _GL_CXXALIAS_SYS (func, rettype, parameters)
   declares a C++ alias called GNULIB_NAMESPACE::func
   that redirects to the system provided function func, if GNULIB_NAMESPACE
   is defined.
   Example:
     _GL_CXXALIAS_SYS (open, int, (const char *filename, int flags, ...));
 */
#if defined __cplusplus && defined GNULIB_NAMESPACE
  /* If we were to write
       rettype (*const func) parameters = ::func;
     like above in _GL_CXXALIAS_RPL_1, the compiler could optimize calls
     better (remove an indirection through a 'static' pointer variable),
     but then the _GL_CXXALIASWARN macro below would cause a warning not only
     for uses of ::func but also for uses of GNULIB_NAMESPACE::func.  */
# define _GL_CXXALIAS_SYS(func,rettype,parameters) \
    namespace GNULIB_NAMESPACE                     \
    {                                              \
      static rettype (*func) parameters = ::func;  \
    }                                              \
    _GL_EXTERN_C int _gl_cxxalias_dummy
#else
# define _GL_CXXALIAS_SYS(func,rettype,parameters) \
    _GL_EXTERN_C int _gl_cxxalias_dummy
#endif

/* _GL_CXXALIASWARN (func);
   causes a warning to be emitted when ::func is used but not when
   GNULIB_NAMESPACE::func is used.  */
#if defined __cplusplus && defined GNULIB_NAMESPACE
# define _GL_CXXALIASWARN(func) \
   _GL_CXXALIASWARN1 (func, GNULIB_NAMESPACE)
# define _GL_CXXALIASWARN1(func,namespace) \
   _GL_CXXALIASWARN2 (func, namespace)
# define _GL_CXXALIASWARN2(func,namespace) \
   _GL_WARN_ON_USE (func, \
                    "The symbol ::" #func " refers to the system function. " \
                    "Use " #namespace "::" #func " instead.")
#else
# define _GL_CXXALIASWARN(func) \
    _GL_EXTERN_C int _gl_cxxalias_dummy
#endif

#endif /* _GL_CXXDEFS_H */