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f434ba03 | 1 | /* A C macro for emitting warnings if a function is used. |
49e4877c | 2 | Copyright (C) 2010-2016 Free Software Foundation, Inc. |
f434ba03 PA |
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 | |
770d76d7 | 12 | General Public License for more details. |
f434ba03 PA |
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 | |
a512b375 | 58 | static char ***rpl_environ (void) { return &environ; } |
f434ba03 PA |
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 |