[Bug c++/67256] New: [C++11] Global scope contaminated with symbols from mathcalls.h

[michal.fita at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67256

            Bug ID: 67256
           Summary: [C++11] Global scope contaminated with symbols from
                    mathcalls.h
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michal.fita at gmail dot com
  Target Milestone: ---

Created attachment 36198
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36198&action=edit
The test code.

I have problem with GCC 4.9.2 on Jessie, where with -std=c++11 I cannot compile
my code. I attached the test example which compiles with:

  g++ -o test g++mathcalls-error.cpp

But doesn't compile with:

  g++ -o test -std=c++11 g++mathcalls-error.cpp

Producing following errors:

g++mathcalls-error.cpp:7:15: error: ‘namespace log { }’ redeclared as different
kind of symbol
 namespace log {
               ^
In file included from /usr/include/features.h:374:0,
                 from
/usr/include/x86_64-linux-gnu/c++/4.9/bits/os_defines.h:39,
                 from
/usr/include/x86_64-linux-gnu/c++/4.9/bits/c++config.h:430,
                 from /usr/include/c++/4.9/utility:68,
                 from /usr/include/c++/4.9/algorithm:60,
                 from g++mathcalls-error.cpp:2:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:109:1: note: previous
declaration ‘double log(double)’
 __MATHCALL (log,, (_Mdouble_ __x));
 ^
g++mathcalls-error.cpp:19:15: error: ‘namespace sin { }’ redeclared as
different kind of symbol
 namespace sin {
               ^
In file included from /usr/include/features.h:374:0,
                 from
/usr/include/x86_64-linux-gnu/c++/4.9/bits/os_defines.h:39,
                 from
/usr/include/x86_64-linux-gnu/c++/4.9/bits/c++config.h:430,
                 from /usr/include/c++/4.9/utility:68,
                 from /usr/include/c++/4.9/algorithm:60,
                 from g++mathcalls-error.cpp:2:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:65:1: note: previous declaration
‘double sin(double)’
 __MATHCALL (sin,, (_Mdouble_ __x));
 ^
g++mathcalls-error.cpp: In function ‘int main()’:
g++mathcalls-error.cpp:28:5: error: ‘log’ is not a class, namespace, or
enumeration
     log::info("Test %s", "sinner");
     ^
g++mathcalls-error.cpp:29:5: error: ‘sin’ is not a class, namespace, or
enumeration
     sin::cardinal(666);
     ^

So, this may not be bug inside the compiler (however studies of inclusion chain
leads nowhere), but with the standard set of headers. This cause symbols
related to math functions be present in global scope instead of std namespace.

This effectively block us from using namespaces like "log" or "sin" in our huge
codebase if we want to move toward C++11 standard.