150 lines
6.8 KiB
C
150 lines
6.8 KiB
C
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/* A C macro for emitting warnings if a function is used.
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Copyright (C) 2010-2021 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published
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by the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* _GL_WARN_ON_USE (function, "literal string") issues a declaration
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for FUNCTION which will then trigger a compiler warning containing
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the text of "literal string" anywhere that function is called, if
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supported by the compiler. If the compiler does not support this
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feature, the macro expands to an unused extern declaration.
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_GL_WARN_ON_USE_ATTRIBUTE ("literal string") expands to the
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attribute used in _GL_WARN_ON_USE. If the compiler does not support
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this feature, it expands to empty.
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These macros are useful for marking a function as a potential
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portability trap, with the intent that "literal string" include
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instructions on the replacement function that should be used
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instead.
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_GL_WARN_ON_USE is for functions with 'extern' linkage.
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_GL_WARN_ON_USE_ATTRIBUTE is for functions with 'static' or 'inline'
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linkage.
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However, one of the reasons that a function is a portability trap is
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if it has the wrong signature. Declaring FUNCTION with a different
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signature in C is a compilation error, so this macro must use the
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same type as any existing declaration so that programs that avoid
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the problematic FUNCTION do not fail to compile merely because they
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included a header that poisoned the function. But this implies that
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_GL_WARN_ON_USE is only safe to use if FUNCTION is known to already
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have a declaration. Use of this macro implies that there must not
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be any other macro hiding the declaration of FUNCTION; but
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undefining FUNCTION first is part of the poisoning process anyway
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(although for symbols that are provided only via a macro, the result
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is a compilation error rather than a warning containing
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"literal string"). Also note that in C++, it is only safe to use if
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FUNCTION has no overloads.
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For an example, it is possible to poison 'getline' by:
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- adding a call to gl_WARN_ON_USE_PREPARE([[#include <stdio.h>]],
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[getline]) in configure.ac, which potentially defines
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HAVE_RAW_DECL_GETLINE
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- adding this code to a header that wraps the system <stdio.h>:
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#undef getline
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#if HAVE_RAW_DECL_GETLINE
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_GL_WARN_ON_USE (getline, "getline is required by POSIX 2008, but"
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"not universally present; use the gnulib module getline");
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#endif
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It is not possible to directly poison global variables. But it is
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possible to write a wrapper accessor function, and poison that
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(less common usage, like &environ, will cause a compilation error
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rather than issue the nice warning, but the end result of informing
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the developer about their portability problem is still achieved):
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#if HAVE_RAW_DECL_ENVIRON
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static char ***
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rpl_environ (void) { return &environ; }
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_GL_WARN_ON_USE (rpl_environ, "environ is not always properly declared");
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# undef environ
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# define environ (*rpl_environ ())
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#endif
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or better (avoiding contradictory use of 'static' and 'extern'):
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#if HAVE_RAW_DECL_ENVIRON
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static char ***
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_GL_WARN_ON_USE_ATTRIBUTE ("environ is not always properly declared")
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rpl_environ (void) { return &environ; }
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# undef environ
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# define environ (*rpl_environ ())
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#endif
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*/
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#ifndef _GL_WARN_ON_USE
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# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
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/* A compiler attribute is available in gcc versions 4.3.0 and later. */
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# define _GL_WARN_ON_USE(function, message) \
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extern __typeof__ (function) function __attribute__ ((__warning__ (message)))
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# define _GL_WARN_ON_USE_ATTRIBUTE(message) \
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__attribute__ ((__warning__ (message)))
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# elif __clang_major__ >= 4
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/* Another compiler attribute is available in clang. */
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# define _GL_WARN_ON_USE(function, message) \
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extern __typeof__ (function) function \
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__attribute__ ((__diagnose_if__ (1, message, "warning")))
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# define _GL_WARN_ON_USE_ATTRIBUTE(message) \
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__attribute__ ((__diagnose_if__ (1, message, "warning")))
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# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
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/* Verify the existence of the function. */
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# define _GL_WARN_ON_USE(function, message) \
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extern __typeof__ (function) function
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# define _GL_WARN_ON_USE_ATTRIBUTE(message)
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# else /* Unsupported. */
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# define _GL_WARN_ON_USE(function, message) \
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_GL_WARN_EXTERN_C int _gl_warn_on_use
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# define _GL_WARN_ON_USE_ATTRIBUTE(message)
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# endif
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#endif
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/* _GL_WARN_ON_USE_CXX (function, rettype_gcc, rettype_clang, parameters_and_attributes, "message")
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is like _GL_WARN_ON_USE (function, "message"), except that in C++ mode the
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function is declared with the given prototype, consisting of return type,
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parameters, and attributes.
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This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does
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not work in this case. */
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#ifndef _GL_WARN_ON_USE_CXX
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# if !defined __cplusplus
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# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \
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_GL_WARN_ON_USE (function, msg)
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# else
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# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
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/* A compiler attribute is available in gcc versions 4.3.0 and later. */
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# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \
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extern rettype_gcc function parameters_and_attributes \
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__attribute__ ((__warning__ (msg)))
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# elif __clang_major__ >= 4
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/* Another compiler attribute is available in clang. */
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# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \
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extern rettype_clang function parameters_and_attributes \
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__attribute__ ((__diagnose_if__ (1, msg, "warning")))
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# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
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/* Verify the existence of the function. */
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# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \
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extern rettype_gcc function parameters_and_attributes
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# else /* Unsupported. */
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# define _GL_WARN_ON_USE_CXX(function,rettype_gcc,rettype_clang,parameters_and_attributes,msg) \
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_GL_WARN_EXTERN_C int _gl_warn_on_use
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# endif
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# endif
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#endif
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/* _GL_WARN_EXTERN_C declaration;
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performs the declaration with C linkage. */
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#ifndef _GL_WARN_EXTERN_C
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# if defined __cplusplus
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# define _GL_WARN_EXTERN_C extern "C"
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# else
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# define _GL_WARN_EXTERN_C extern
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# endif
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#endif
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