[Bug c++/54526] New: <:: is incorrectly treated as digraph <: followed by colon

["tsoae at mail dot ru" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54526

             Bug #: 54526
           Summary: <:: is incorrectly treated as digraph <: followed by
                    colon
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tsoae@mail.ru


g++ 4.8.0 20120826 (experimental) fails to compile the following well-defined
code:

    template <class T>
        struct X {};

    struct A {};

    int main()
    {
        X<::A> x; // error: ‘<::’ cannot begin a template-argument list
    }

According to C++11 - 2.5 p3, bullet 2:

If the input stream has been parsed into preprocessing tokens up to a given
character:
... if the next three characters are <:: and the subsequent character is
neither : nor >, the < is treated as a preprocessor token by itself and not as
the first character of the alternative token <:.

Compiler version info:

Target: i686-pc-linux-gnu
Configured with: .../configure --prefix=.../target --enable-languages=c,c++
Thread model: posix
gcc version 4.8.0 20120826 (experimental) (GCC)

Command line:

g++ test.cpp -std=c++11 -pedantic-errors

Diagnostic message:

test.cpp: In function ‘int main()’:
test.cpp:8:10: error: ‘<::’ cannot begin a template-argument list
[-fpermissive]
         X<::A> x;
          ^
test.cpp:8:10: note: ‘<:’ is an alternate spelling for ‘[’. Insert whitespace
between ‘<’ and ‘::’
test.cpp:8:10: note: (if you use ‘-fpermissive’ G++ will accept your code)