Recursive Include with no cpp and no forward decalaration

Question

I have two files one calling the other with hpp guards that I am not including. I get an error saying :

provider.hpp: error C2653: 'data': is not a class or namespace name

This is because of the declaration, I believe:

static std::string provider::get(const data::details& details)

The following code:

// provider.hpp

#include <data.hpp>
class provider
{
public:
    static std::string get(const data::details& details)
    {
        static provider me;
        return me.private_get(details);
    };

    std::string private_get(const data::details& details) const
    {
        return "this is data";
    };
};

and I have something like this in another file:

// data.hpp

#include <provider.hpp>
class data
{
public:
    class details
    {
        //bla bla
        std::string m_name;
    };
public:
    data(const data::details& details)
    {
        m_data = provider::get(details);
    };

private:
    std::string m_data;
};

You can see that one file uses the other. Please could you help me solve this problem under the following restriction please:

1. I don't want to add any files (unless there is no solution you can think off).
2. I don't want to use the cpp (unless there is no solution you can think off).
3. I want to keep the design as it is (unless there is no solution you can think off).

Forward declaration wouldn't work because I am not only using the type.