[Bug c++/37374] New: "using" shadows declaration

["kduda at arastra dot com" <gcc-bugzilla at gcc dot gnu dot org>]

The following code (example A) compiles:

  namespace N1 { void f() {} }
  namespace N2 { void f(int) {} using N1::f; }
  main() { N2::f(0); }

But this code does not compile (example B) because the compiler claims there is
no f(int) within N2:

  namespace N1 { void f() {} }
  namespace N2 { void f(int); using N1::f; }
  void N2::f(int) {}
  main() { N2::f(0); }

I do not have the C++ expertise to know whether the "using N1::f" should shadow
the previous use of the unqualified name "f" inside "N2", but I do think that
it should be consistent for function declarations vs function definitions. 
That is, if "using N1::f" should shadow the prior use of "f" within "N2", then
example A should not compile because the N2::f with the (int) overload has been
shadowed.  If "using N1::f" should not shadow the prior use of f within N2,
then example B should compile because N2::f(int) was properly declared in
namespace N2.

Example B used to compile in g++-4.1.2.  It was in upgrading to 4.3.0 that code
in our tree that is like example B suddenly stopped compiling.

I apologize that I do not know what the bug is --- is g++ incorrectly allowing
example A to compile, or is it incorrectly giving an error with example B?   I
do not know, but it seems that one must be wrong.

Also, I apologize in advance if gcc's behavior is correct here, and somehow it
is right that A should compile and B should not.  I find the rules around
unqualified name resolution, "using", and function overloading difficult to
understand.  Any explanation greatly appreciated.

Whatever the result, the workaround is easy of course --- just move the "using
N1::f" before any other use of "f" within N2.  Then there is no question about
what sorts of uses of "f" should be shadowed.

Thanks,
    -Ken


-- 
           Summary: "using" shadows declaration
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kduda at arastra dot com
 GCC build triplet: i386-redhat-linux
  GCC host triplet: i386-redhat-linux
GCC target triplet: i386-redhat-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37374