Return to warn-on-use.h CVS log

Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / libiconv / build-aux / snippet

Annotation of embedaddon/libiconv/build-aux/snippet/warn-on-use.h, revision 1.1.1.1

1.1       misho       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