| 1 | /* A C macro for emitting warnings if a function is used.
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| 2 | Copyright (C) 2010-2012 Free Software Foundation, Inc.
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| 3 |
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| 4 | This program is free software: you can redistribute it and/or modify it
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| 5 | under the terms of the GNU General Public License as published
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| 6 | by the Free Software Foundation; either version 3 of the License, or
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| 7 | (at your option) any later version.
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| 8 |
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| 9 | This program is distributed in the hope that it will be useful,
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 12 | General Public License for more details.
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| 13 |
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| 14 | You should have received a copy of the GNU General Public License
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| 15 | along with this program. If not, see <http://www.gnu.org/licenses/>. */
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| 16 |
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| 17 | /* _GL_WARN_ON_USE (function, "literal string") issues a declaration
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| 18 | for FUNCTION which will then trigger a compiler warning containing
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| 19 | the text of "literal string" anywhere that function is called, if
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| 20 | supported by the compiler. If the compiler does not support this
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| 21 | feature, the macro expands to an unused extern declaration.
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| 22 |
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| 23 | This macro is useful for marking a function as a potential
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| 24 | portability trap, with the intent that "literal string" include
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| 25 | instructions on the replacement function that should be used
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| 26 | instead. However, one of the reasons that a function is a
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| 27 | portability trap is if it has the wrong signature. Declaring
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| 28 | FUNCTION with a different signature in C is a compilation error, so
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| 29 | this macro must use the same type as any existing declaration so
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| 30 | that programs that avoid the problematic FUNCTION do not fail to
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| 31 | compile merely because they included a header that poisoned the
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| 32 | function. But this implies that _GL_WARN_ON_USE is only safe to
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| 33 | use if FUNCTION is known to already have a declaration. Use of
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| 34 | this macro implies that there must not be any other macro hiding
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| 35 | the declaration of FUNCTION; but undefining FUNCTION first is part
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| 36 | of the poisoning process anyway (although for symbols that are
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| 37 | provided only via a macro, the result is a compilation error rather
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| 38 | than a warning containing "literal string"). Also note that in
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| 39 | C++, it is only safe to use if FUNCTION has no overloads.
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| 40 |
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| 41 | For an example, it is possible to poison 'getline' by:
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| 42 | - adding a call to gl_WARN_ON_USE_PREPARE([[#include <stdio.h>]],
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| 43 | [getline]) in configure.ac, which potentially defines
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| 44 | HAVE_RAW_DECL_GETLINE
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| 45 | - adding this code to a header that wraps the system <stdio.h>:
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| 46 | #undef getline
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| 47 | #if HAVE_RAW_DECL_GETLINE
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| 48 | _GL_WARN_ON_USE (getline, "getline is required by POSIX 2008, but"
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| 49 | "not universally present; use the gnulib module getline");
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| 50 | #endif
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| 51 |
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| 52 | It is not possible to directly poison global variables. But it is
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| 53 | possible to write a wrapper accessor function, and poison that
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| 54 | (less common usage, like &environ, will cause a compilation error
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| 55 | rather than issue the nice warning, but the end result of informing
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| 56 | the developer about their portability problem is still achieved):
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| 57 | #if HAVE_RAW_DECL_ENVIRON
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| 58 | static inline char ***rpl_environ (void) { return &environ; }
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| 59 | _GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared");
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| 60 | # undef environ
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| 61 | # define environ (*rpl_environ ())
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| 62 | #endif
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| 63 | */
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| 64 | #ifndef _GL_WARN_ON_USE
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| 65 |
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| 66 | # if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
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| 67 | /* A compiler attribute is available in gcc versions 4.3.0 and later. */
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| 68 | # define _GL_WARN_ON_USE(function, message) \
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| 69 | extern __typeof__ (function) function __attribute__ ((__warning__ (message)))
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| 70 | # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
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| 71 | /* Verify the existence of the function. */
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| 72 | # define _GL_WARN_ON_USE(function, message) \
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| 73 | extern __typeof__ (function) function
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| 74 | # else /* Unsupported. */
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| 75 | # define _GL_WARN_ON_USE(function, message) \
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| 76 | _GL_WARN_EXTERN_C int _gl_warn_on_use
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| 77 | # endif
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| 78 | #endif
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| 79 |
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| 80 | /* _GL_WARN_ON_USE_CXX (function, rettype, parameters_and_attributes, "string")
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| 81 | is like _GL_WARN_ON_USE (function, "string"), except that the function is
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| 82 | declared with the given prototype, consisting of return type, parameters,
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| 83 | and attributes.
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| 84 | This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does
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| 85 | not work in this case. */
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| 86 | #ifndef _GL_WARN_ON_USE_CXX
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| 87 | # if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
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| 88 | # define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
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| 89 | extern rettype function parameters_and_attributes \
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| 90 | __attribute__ ((__warning__ (msg)))
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| 91 | # elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
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| 92 | /* Verify the existence of the function. */
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| 93 | # define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
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| 94 | extern rettype function parameters_and_attributes
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| 95 | # else /* Unsupported. */
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| 96 | # define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
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| 97 | _GL_WARN_EXTERN_C int _gl_warn_on_use
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| 98 | # endif
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| 99 | #endif
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| 100 |
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| 101 | /* _GL_WARN_EXTERN_C declaration;
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| 102 | performs the declaration with C linkage. */
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| 103 | #ifndef _GL_WARN_EXTERN_C
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| 104 | # if defined __cplusplus
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| 105 | # define _GL_WARN_EXTERN_C extern "C"
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| 106 | # else
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| 107 | # define _GL_WARN_EXTERN_C extern
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| 108 | # endif
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| 109 | #endif
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