source: grub-pc/trunk/fuentes/build-aux/snippet/warn-on-use.h @ 22

Last change on this file since 22 was 22, checked in by mabarracus, 4 years ago

updated version and apply net.ifnames=0 into debian/rules

File size: 5.0 KB
Line 
1/* A C macro for emitting warnings if a function is used.
2   Copyright (C) 2010-2013 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 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) \
69extern __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) \
73extern __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) \
89extern 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) \
94extern 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
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