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.
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) \
