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Diffstat (limited to 'lib/warn-on-use.h')
| -rw-r--r-- | lib/warn-on-use.h | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/lib/warn-on-use.h b/lib/warn-on-use.h new file mode 100644 index 00000000..d46b4858 --- /dev/null +++ b/lib/warn-on-use.h @@ -0,0 +1,118 @@ +/* A C macro for emitting warnings if a function is used. + Copyright (C) 2010-2017 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or + modify it under the terms of either: + + * the GNU Lesser General Public License as published by the Free + Software Foundation; either version 3 of the License, or (at your + option) any later version. + + or + + * the GNU General Public License as published by the Free + Software Foundation; either version 2 of the License, or (at your + option) any later version. + + or both in parallel, as here. + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* _GL_WARN_ON_USE (function, "literal string") issues a declaration + for FUNCTION which will then trigger a compiler warning containing + the text of "literal string" anywhere that function is called, if + supported by the compiler. If the compiler does not support this + feature, the macro expands to an unused extern declaration. + + This macro is useful for marking a function as a potential + portability trap, with the intent that "literal string" include + instructions on the replacement function that should be used + instead. However, one of the reasons that a function is a + portability trap is if it has the wrong signature. Declaring + FUNCTION with a different signature in C is a compilation error, so + this macro must use the same type as any existing declaration so + that programs that avoid the problematic FUNCTION do not fail to + compile merely because they included a header that poisoned the + function. But this implies that _GL_WARN_ON_USE is only safe to + use if FUNCTION is known to already have a declaration. Use of + this macro implies that there must not be any other macro hiding + the declaration of FUNCTION; but undefining FUNCTION first is part + of the poisoning process anyway (although for symbols that are + provided only via a macro, the result is a compilation error rather + than a warning containing "literal string"). Also note that in + C++, it is only safe to use if FUNCTION has no overloads. + + For an example, it is possible to poison 'getline' by: + - adding a call to gl_WARN_ON_USE_PREPARE([[#include <stdio.h>]], + [getline]) in configure.ac, which potentially defines + HAVE_RAW_DECL_GETLINE + - adding this code to a header that wraps the system <stdio.h>: + #undef getline + #if HAVE_RAW_DECL_GETLINE + _GL_WARN_ON_USE (getline, "getline is required by POSIX 2008, but" + "not universally present; use the gnulib module getline"); + #endif + + It is not possible to directly poison global variables. But it is + possible to write a wrapper accessor function, and poison that + (less common usage, like &environ, will cause a compilation error + rather than issue the nice warning, but the end result of informing + the developer about their portability problem is still achieved): + #if HAVE_RAW_DECL_ENVIRON + static char ***rpl_environ (void) { return &environ; } + _GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared"); + # undef environ + # define environ (*rpl_environ ()) + #endif + */ +#ifndef _GL_WARN_ON_USE + +# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__) +/* A compiler attribute is available in gcc versions 4.3.0 and later. */ +# define _GL_WARN_ON_USE(function, message) \ +extern __typeof__ (function) function __attribute__ ((__warning__ (message))) +# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING +/* Verify the existence of the function. */ +# define _GL_WARN_ON_USE(function, message) \ +extern __typeof__ (function) function +# else /* Unsupported. */ +# define _GL_WARN_ON_USE(function, message) \ +_GL_WARN_EXTERN_C int _gl_warn_on_use +# endif +#endif + +/* _GL_WARN_ON_USE_CXX (function, rettype, parameters_and_attributes, "string") + is like _GL_WARN_ON_USE (function, "string"), except that the function is + declared with the given prototype, consisting of return type, parameters, + and attributes. + This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does + not work in this case. */ +#ifndef _GL_WARN_ON_USE_CXX +# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__) +# define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \ +extern rettype function parameters_and_attributes \ + __attribute__ ((__warning__ (msg))) +# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING +/* Verify the existence of the function. */ +# define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \ +extern rettype function parameters_and_attributes +# else /* Unsupported. */ +# define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \ +_GL_WARN_EXTERN_C int _gl_warn_on_use +# endif +#endif + +/* _GL_WARN_EXTERN_C declaration; + performs the declaration with C linkage. */ +#ifndef _GL_WARN_EXTERN_C +# if defined __cplusplus +# define _GL_WARN_EXTERN_C extern "C" +# else +# define _GL_WARN_EXTERN_C extern +# endif +#endif |