false "syntax error: != <" on friend template function

[David Garlisch]

Snippet compiler: https://coliru.stacked-crooked.com/view?id=1a00c4e44f0c7506

#include <iostream>

template <typename T> class Foo;

template <typename T>
bool operator==(const Foo<T> &, const Foo<T> &);

template <typename T>
bool operator!=(const Foo<T> &, const Foo<T> &);

template <typename T>
class Foo {
public:
    Foo()
    {
    }


    //--------------------------------------------------------------------------
    //--------------------------------------------------------------------------
    // Leaving off <> makes CPPCHECK happy but generates a G++ warning
    friend bool operator== (const Foo<T> &, const Foo<T> &);
    //
    // main.cpp:24:65: warning: friend declaration 'bool operator==(const Foo<T>&, const Foo<T>&)' declares a non-template function [-Wnon-template-friend]
    // friend bool operator== (const Foo<T> &, const Foo<T> &);
    //                                                       ^
    // main.cpp:24:65:note:(if this is not what you intended, make sure
    //   the function template has already been declared and add <> after the
    //   function name here)


    //--------------------------------------------------------------------------
    //--------------------------------------------------------------------------
    // This fails CPPCHECK - but builds w/o warning on gcc 5.2 (C++11)
    // I believe this is the correct syntax for a non-inline friend template function.
    // See: Template friend operators
    // https://en.cppreference.com/w/cpp/language/friend
    friend bool operator!= <> (const Foo<T> &, const Foo<T> &);

private:
    T impl_{ 0 };
};


template <typename T>
bool operator== (const Foo<T> &a, const Foo<T> &b)
{
    std::cout << "hello ==\n";
    return a.impl_ == b.impl_;
}


template <typename T>
bool operator!= (const Foo<T> &a, const Foo<T> &b)
{
    std::cout << "hello !=\n";
    return a.impl_ == b.impl_;
}



int main()
{
    Foo<int> v1;
    Foo<int> v2;
    v1 == v2;
    v1 != v2;
}

[Daniel Marjamäki]

Thanks! I can reproduce. I created this ticket: https://trac.cppcheck.net/ticket/9771