[Bug c++/57883] New: Feature request: better diagnostic for unknown type

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57883

            Bug ID: 57883
           Summary: Feature request: better diagnostic for unknown type
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dushistov at mail dot ru

$cat test.cpp
//#include <cstddef>
struct vec {
    double x;
    double y;
    double z;

    double& operator[](size_t i) {
        switch (i) {
        case 0:
            return x;
        case 1:
            return y;
        case 2:
            return z;
        }
    }
};

g++ -c -Wall -std=c++11 test.cpp
test.cpp:8:21: error: declaration of 'operator[]' as non-function
  double& operator[](size_t i) {

plus more not related errors 
...

This is completly wrong message, but at the same time 
clang++ -c -Wall -std=c++11 test.cpp
test.cpp:8:21: error: unknown type name 'size_t'
        double& operator[](size_t i) {
                           ^
1 error generated.

It will be good if gcc also can give error with message that size_t undefined.