Missing lifetime specifier on functions returning concrete templates

[BabaBert]

This might be an edge case but when a function returnr a reference to an innner templated member of an outer class or struct like this:

template <typename T> class B{
public:
    T& data;
};
class C{};
class A{
    public:
        B<C> data;
    };
B<C>& getInner(A& outer){
    return outer.data;
}

with macro usage like this:

generate!("A")
generate!("B")
generate!("C")
concrete!("B<C>", B_C)
generate!("getInner")

the autocxx generated rust code will have missing lifetime specifiers:

�[0m�[31m  |fn getInner (outer : Pin < & mut A >) -> Pin < & mut B_C > ;
�[0m�[31m  |                                                ^ expected named lifetime parameter
�[0m�[31m  |
�[0m�[31m  = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
�[0m�[31mhelp: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static`

[BabaBert]

So the issue seems to be that the compiler can't derive the lifetime in this case. CXX generates the implementation differently for concrete types, and therefore Rusts elision rules aren't applicable.

[adetaylor]

Thanks for this - would you raise a PR for your tests?