[Bug c++/58724] New: doc: use of attributes for namespace is not clear

["akim.demaille at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58724

            Bug ID: 58724
           Summary: doc: use of attributes for namespace is not clear
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: akim.demaille at gmail dot com

Hi friends,

I could not find an example of a use of the attributes for namespaces.  It is
mentioned in the text body, but there is no example of the syntax (it appears
for the documentation of "visibility" in
http://gcc.gnu.org/onlinedocs/gcc-4.8.1/gcc/Function-Attributes.html#Function-Attributes).
 Also, it does not appear in the node dedicated to C++ attributes
(http://gcc.gnu.org/onlinedocs/gcc-4.8.1/gcc/C_002b_002b-Attributes.html#C_002b_002b-Attributes).

Also, it might be worth noting (in the doc) that the __attribute__ syntax is
supported, but not [[...]].  I have no idea if this is meant.  4.8 issues a
weird error message, 4.9 ices.

$ cat foo.cc
namespace foo __attribute__((visibility("default"))) {}
namespace bar [[gnu::visibility("default")]] {}
$ g++-mp-4.8 -std=c++1y foo.cc -c
foo.cc:2:46: warning: '#'tree_list' not supported by dump_decl#<declaration
error>' attribute directive ignored [-Wattributes]
 namespace bar [[gnu::visibility("default")]] {}
                                              ^
$ g++-mp-4.9 -std=c++1y foo.cc -c
foo.cc:2:46: internal compiler error: tree check: expected identifier_node,
have tree_list in private_is_attribute_p, at tree.c:5558
 namespace bar [[gnu::visibility("default")]] {}
                                              ^

foo.cc:2:46: internal compiler error: Abort trap: 6
g++-mp-4.9: internal compiler error: Abort trap: 6 (program cc1plus)
zsh: abort      g++-mp-4.9 -std=c++1y foo.cc -c
$ g++-mp-4.9 --version                                          13
g++-mp-4.9 (MacPorts gcc49 4.9-20130915_0) 4.9.0 20130915 (experimental)
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