On Tue, Dec 3, 2019, 02:31 Bruno Haible <br...@clisp.org> wrote: > Hi Christian, > > > $ /opt/IBM/xlC/16.1.0/bin/xlclang++ test.cc -I gnulib/import -I > > ../gnulib/import/ > > In file included from test.cc:2: > > In file included from gnulib/import/stdlib.h:36: > > In file included from /opt/IBM/xlC/16.1.0/include2/c++/stdlib.h:94: > > /opt/IBM/xlC/16.1.0/include2/aix/stdlib.h:310:9: error: an attribute > > list cannot appear here > > extern _Noreturn void exit(int); > > ^~~~~~~~~ > > ./gnulib/config.h:1117:21: note: expanded from macro '_Noreturn' > > # define _Noreturn [[noreturn]] > > ^~~~~~~~~~~~ > > In file included from test.cc:2: > > In file included from gnulib/import/stdlib.h:36: > > In file included from /opt/IBM/xlC/16.1.0/include2/c++/stdlib.h:94: > > /opt/IBM/xlC/16.1.0/include2/aix/stdlib.h:319:9: error: an attribute > > list cannot appear here > > extern _Noreturn void quick_exit(int); > > ^~~~~~~~~ > > ./gnulib/config.h:1117:21: note: expanded from macro '_Noreturn' > > # define _Noreturn [[noreturn]] > > ^~~~~~~~~~~~ > > 2 errors generated. > > Oh boy. While the syntax > > [[noreturn]] void func (...); > > and > > [[noreturn]] extern void func (...); > > are valid in C++, the syntax > > extern [[noreturn]] void func (...); > > is not. (clang and MSVC give an error, and gcc a warning.) One more example > of how terrible C++ is at the syntactic level. > > Since not only the aforementioned AIX header file, but also several gnulib > header files use the 'extern' keyword consistently (in a good way), the > only choice we have is to not use '[[noreturn]]' - except in noreturn.h > which documents the allowed syntaxes clearly. >
Thank you! Any ideas about the error I mentioned in the first email in this thread, about mbslen etc.? Thanks, Christian > 2019-12-03 Bruno Haible <br...@clisp.org> > > Avoid hassles caused by [[noreturn]] in C++. > Reported by Christian Biesinger <cbiesin...@google.com> in > < > https://lists.gnu.org/archive/html/bug-gnulib/2019-12/msg00010.html>. > * m4/gnulib-common.m4 (gl_COMMON_BODY): Disable the use of > [[noreturn]]. > * lib/_Noreturn.h: Likewise. > > diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4 > index 479c9de..d8f0d3f 100644 > --- a/m4/gnulib-common.m4 > +++ b/m4/gnulib-common.m4 > @@ -1,4 +1,4 @@ > -# gnulib-common.m4 serial 45 > +# gnulib-common.m4 serial 46 > dnl Copyright (C) 2007-2019 Free Software Foundation, Inc. > dnl This file is free software; the Free Software Foundation > dnl gives unlimited permission to copy and/or distribute it, > @@ -19,7 +19,14 @@ AC_DEFUN([gl_COMMON_BODY], [ > #ifndef _Noreturn > # if (defined __cplusplus \ > && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == > 7)) \ > - || (defined _MSC_VER && 1900 <= _MSC_VER))) > + || (defined _MSC_VER && 1900 <= _MSC_VER)) \ > + && 0) > + /* [[noreturn]] is not practically usable, because with it the syntax > + extern _Noreturn void func (...); > + would not be valid; such a declaration would only be valid with > 'extern' > + and '_Noreturn' swapped, or without the 'extern' keyword. > However, some > + AIX system header files and several gnulib header files use > precisely > + this syntax with 'extern'. */ > # define _Noreturn [[noreturn]] > # elif ((!defined __cplusplus || defined __clang__) \ > && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \ > diff --git a/lib/_Noreturn.h b/lib/_Noreturn.h > index 06320b8..d99e377 100644 > --- a/lib/_Noreturn.h > +++ b/lib/_Noreturn.h > @@ -17,7 +17,14 @@ > #ifndef _Noreturn > # if (defined __cplusplus \ > && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == > 7)) \ > - || (defined _MSC_VER && 1900 <= _MSC_VER))) > + || (defined _MSC_VER && 1900 <= _MSC_VER)) \ > + && 0) > + /* [[noreturn]] is not practically usable, because with it the syntax > + extern _Noreturn void func (...); > + would not be valid; such a declaration would only be valid with > 'extern' > + and '_Noreturn' swapped, or without the 'extern' keyword. > However, some > + AIX system header files and several gnulib header files use > precisely > + this syntax with 'extern'. */ > # define _Noreturn [[noreturn]] > # elif ((!defined __cplusplus || defined __clang__) \ > && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \ > >
