diff options
Diffstat (limited to 'src/gl/warn-on-use.h')
| -rw-r--r-- | src/gl/warn-on-use.h | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/src/gl/warn-on-use.h b/src/gl/warn-on-use.h new file mode 100644 index 0000000..5d5b17f --- /dev/null +++ b/src/gl/warn-on-use.h @@ -0,0 +1,149 @@ +/* A C macro for emitting warnings if a function is used. + Copyright (C) 2010-2021 Free Software Foundation, Inc. + + This program is free software: you can redistribute it and/or modify it + under the terms of the GNU General Public License as published + by the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + 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 + General Public License for more details. + + You should have received a copy of the GNU 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. + + _GL_WARN_ON_USE_ATTRIBUTE ("literal string") expands to the + attribute used in _GL_WARN_ON_USE. If the compiler does not support + this feature, it expands to empty. + + These macros are 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. + _GL_WARN_ON_USE is for functions with 'extern' linkage. + _GL_WARN_ON_USE_ATTRIBUTE is for functions with 'static' or 'inline' + linkage. + + 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 + or better (avoiding contradictory use of 'static' and 'extern'): + #if HAVE_RAW_DECL_ENVIRON + static char *** + _GL_WARN_ON_USE_ATTRIBUTE ("environ is not always properly declared") + rpl_environ (void) { return &environ; } + # 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))) +# define _GL_WARN_ON_USE_ATTRIBUTE(message) \ + __attribute__ ((__warning__ (message))) +# elif __clang_major__ >= 4 +/* Another compiler attribute is available in clang. */ +# define _GL_WARN_ON_USE(function, message) \ +extern __typeof__ (function) function \ + __attribute__ ((__diagnose_if__ (1, message, "warning"))) +# define _GL_WARN_ON_USE_ATTRIBUTE(message) \ + __attribute__ ((__diagnose_if__ (1, message, "warning"))) +# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING +/* Verify the existence of the function. */ +# define _GL_WARN_ON_USE(function, message) \ +extern __typeof__ (function) function +# define _GL_WARN_ON_USE_ATTRIBUTE(message) +# else /* Unsupported. */ +# define _GL_WARN_ON_USE(function, message) \ +_GL_WARN_EXTERN_C int _gl_warn_on_use +# define _GL_WARN_ON_USE_ATTRIBUTE(message) +# endif +#endif + +/* _GL_WARN_ON_USE_CXX (function, rettype_gcc, rettype_clang, parameters_and_attributes, "message") + is like _GL_WARN_ON_USE (function, "message"), except that in C++ mode 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 !defined __cplusplus +# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ + _GL_WARN_ON_USE (function, msg) +# else +# 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_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ +extern rettype_gcc function parameters_and_attributes \ + __attribute__ ((__warning__ (msg))) +# elif __clang_major__ >= 4 +/* Another compiler attribute is available in clang. */ +# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ +extern rettype_clang function parameters_and_attributes \ + __attribute__ ((__diagnose_if__ (1, msg, "warning"))) +# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING +/* Verify the existence of the function. */ +# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ +extern rettype_gcc function parameters_and_attributes +# else /* Unsupported. */ +# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \ +_GL_WARN_EXTERN_C int _gl_warn_on_use +# endif +# 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 |