sycl::buffer::set_final_data is tested with std::shared_ptr which is not required by the spec

[nilsfriess]

In the spec, the templated type Destination of the parameter finalData that is passed to sycl::buffer::set_final_data is described as:

Destination can be either an output iterator or a std::weak_ptr.

In the buffer tests (specifically in this file, lines 66 and 69), set_final_data is also tested with Destination == std::weak_ptr<T[]> and Destination == std::shared_ptr<T[]>, and I don't think that these types are required as per the spec.

So I think either the spec has to be extended or these test cases should be removed from the CTS (and a test case for Destination == std::weak_ptr<T> should be added).

[gmlueck]

I agree that the spec is not clear and that there is a disconnect with the test suite. Looking at the DPC++ implementation, it seems that we allow Destination to be any type that is convertible to std::weak_ptr, though the spec doesn't say that. This is why DPC++ accepts std::shared_ptr.

The spec is also not clear about what type of std::weak_ptr is allowed for Destination. Must it be std::weak_ptr<T>, or can it be std::weak_ptr<T[]>? What about std::weak_ptr<U>, where T is convertible to U?

We might also want to tighten up the specification to say that the output iterator must allow writing objects of type T.

[keryell]

I think this is because at some point in the SYCL 1.2 specification there was some special handling for std::shared_ptr but also std::shared_ptr in some other places. Then I realized that they were redundant because of some implicit conversions.

[gmlueck]

Implicit conversions happen only after template selection, though. The problem is that set_final_data is defined like:

template <typename Destination = std::nullptr_t>
void set_final_data(Destination finalData = nullptr);

Constraints: Available only when Destination is an output iterator or is std::weak_ptr<T>.

If the user calls set_final_data with std::shared_ptr<T>, then the template doesn't add any candidates to the overload set because Destination doesn't satisfy the constraints. If we want to allow std::shared_ptr<T> as an argument type, we need to add it somehow to the constraints.