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libiconv v1.14

    1: /* A C macro for emitting warnings if a function is used.
    2:    Copyright (C) 2010-2011 Free Software Foundation, Inc.
    3: 
    4:    This program is free software: you can redistribute it and/or modify it
    5:    under the terms of the GNU General Public License as published
    6:    by the Free Software Foundation; either version 3 of the License, or
    7:    (at your option) any later version.
    8: 
    9:    This program is distributed in the hope that it will be useful,
   10:    but WITHOUT ANY WARRANTY; without even the implied warranty of
   11:    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   12:    General Public License for more details.
   13: 
   14:    You should have received a copy of the GNU General Public License
   15:    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
   16: 
   17: /* _GL_WARN_ON_USE (function, "literal string") issues a declaration
   18:    for FUNCTION which will then trigger a compiler warning containing
   19:    the text of "literal string" anywhere that function is called, if
   20:    supported by the compiler.  If the compiler does not support this
   21:    feature, the macro expands to an unused extern declaration.
   22: 
   23:    This macro is useful for marking a function as a potential
   24:    portability trap, with the intent that "literal string" include
   25:    instructions on the replacement function that should be used
   26:    instead.  However, one of the reasons that a function is a
   27:    portability trap is if it has the wrong signature.  Declaring
   28:    FUNCTION with a different signature in C is a compilation error, so
   29:    this macro must use the same type as any existing declaration so
   30:    that programs that avoid the problematic FUNCTION do not fail to
   31:    compile merely because they included a header that poisoned the
   32:    function.  But this implies that _GL_WARN_ON_USE is only safe to
   33:    use if FUNCTION is known to already have a declaration.  Use of
   34:    this macro implies that there must not be any other macro hiding
   35:    the declaration of FUNCTION; but undefining FUNCTION first is part
   36:    of the poisoning process anyway (although for symbols that are
   37:    provided only via a macro, the result is a compilation error rather
   38:    than a warning containing "literal string").  Also note that in
   39:    C++, it is only safe to use if FUNCTION has no overloads.
   40: 
   41:    For an example, it is possible to poison 'getline' by:
   42:    - adding a call to gl_WARN_ON_USE_PREPARE([[#include <stdio.h>]],
   43:      [getline]) in configure.ac, which potentially defines
   44:      HAVE_RAW_DECL_GETLINE
   45:    - adding this code to a header that wraps the system <stdio.h>:
   46:      #undef getline
   47:      #if HAVE_RAW_DECL_GETLINE
   48:      _GL_WARN_ON_USE (getline, "getline is required by POSIX 2008, but"
   49:        "not universally present; use the gnulib module getline");
   50:      #endif
   51: 
   52:    It is not possible to directly poison global variables.  But it is
   53:    possible to write a wrapper accessor function, and poison that
   54:    (less common usage, like &environ, will cause a compilation error
   55:    rather than issue the nice warning, but the end result of informing
   56:    the developer about their portability problem is still achieved):
   57:    #if HAVE_RAW_DECL_ENVIRON
   58:    static inline char ***rpl_environ (void) { return &environ; }
   59:    _GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared");
   60:    # undef environ
   61:    # define environ (*rpl_environ ())
   62:    #endif
   63:    */
   64: #ifndef _GL_WARN_ON_USE
   65: 
   66: # if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
   67: /* A compiler attribute is available in gcc versions 4.3.0 and later.  */
   68: #  define _GL_WARN_ON_USE(function, message) \
   69: extern __typeof__ (function) function __attribute__ ((__warning__ (message)))
   70: # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
   71: /* Verify the existence of the function.  */
   72: #  define _GL_WARN_ON_USE(function, message) \
   73: extern __typeof__ (function) function
   74: # else /* Unsupported.  */
   75: #  define _GL_WARN_ON_USE(function, message) \
   76: _GL_WARN_EXTERN_C int _gl_warn_on_use
   77: # endif
   78: #endif
   79: 
   80: /* _GL_WARN_ON_USE_CXX (function, rettype, parameters_and_attributes, "string")
   81:    is like _GL_WARN_ON_USE (function, "string"), except that the function is
   82:    declared with the given prototype, consisting of return type, parameters,
   83:    and attributes.
   84:    This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does
   85:    not work in this case.  */
   86: #ifndef _GL_WARN_ON_USE_CXX
   87: # if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
   88: #  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
   89: extern rettype function parameters_and_attributes \
   90:      __attribute__ ((__warning__ (msg)))
   91: # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
   92: /* Verify the existence of the function.  */
   93: #  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
   94: extern rettype function parameters_and_attributes
   95: # else /* Unsupported.  */
   96: #  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
   97: _GL_WARN_EXTERN_C int _gl_warn_on_use
   98: # endif
   99: #endif
  100: 
  101: /* _GL_WARN_EXTERN_C declaration;
  102:    performs the declaration with C linkage.  */
  103: #ifndef _GL_WARN_EXTERN_C
  104: # if defined __cplusplus
  105: #  define _GL_WARN_EXTERN_C extern "C"
  106: # else
  107: #  define _GL_WARN_EXTERN_C extern
  108: # endif
  109: #endif