[Bug c++/47999] New: [C++0x] auto type deduction works incorrectly in a function template

["mimomorin at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47999

           Summary: [C++0x] auto type deduction works incorrectly in a
                    function template
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mimomorin@gmail.com


Created attachment 23554
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23554
Test case

When `auto&&` is initialized with a function return value that is an lvalue
reference, the deduced type should be an lvalue reference. 

    int& identity(int& i) { return i; }

    void f()
    {
        int i = 0;
        auto&& x = identity(i); // x has type `int&`
    }

But, in a function template, auto type deduction incorrectly deduces
the type as an rvalue reference. 

    template <typename T>
    void f()
    {
        int i = 0;
        auto&& x = identity(i); // BUG: x has type `int&&`
    }

This bug leads to compilation error in gcc 4.5 and 4.6, 
because lvalues cannot bind to rvalue references. 
In gcc 4.4, the code compiles fine because lvalues are 
allowed to bind to rvalue references.

Tested compilers: gcc-4.4.5, 4.5.2, 4.6-20110219.
(This problem was found by Nathan Ridge.)