def context_processor(self, func):
        """ Decorate a given function to use as a context processor.

        ::
            @app.ps.jinja2.context_processor
            def my_context():
                return {...}
        """
        func = to_coroutine(func)
        self.providers.append(func)
        return func
Decorate a given function to use as a context processor.

        ::
            @app.ps.jinja2.context_processor
            def my_context():
                return {...}