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+/* 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 Lesser General Public License as published
+ by the Free Software Foundation; either version 2 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
+ 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.
+
+ _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