[BUG]: cuda::std::span<bool> brace initialization fails with narrowing conversion error

[PointKernel]

Is this a duplicate?

• I confirmed there appear to be no duplicate issues for this bug and that I agree to the Code of Conduct

Type of Bug

Compile-time Error

Component

libcu++

Describe the bug

Brace initialization {} of cuda::std::span<bool> fails with narrowing conversion errors, while parentheses initialization () works. This inconsistency is due to cuda::std::span<bool> internally using __nv_bool instead of bool.

How to Reproduce

https://godbolt.org/z/h4cM67hsT

Expected behavior

cuda::std::span should build and work as std::span in the given sample code.

Reproduction link

https://godbolt.org/z/h4cM67hsT

Operating System

No response

nvidia-smi output

No response

NVCC version

No response

[miscco]

Unfortunately, this looks like it is not an issue with our implementation, but some unfortunate interaction with the new initilizer_list constructor from C++26

explicit(extent != std::dynamic_extent)
constexpr span( std::initializer_list<value_type> il ) noexcept;

If you try the same code with C++26, it will also fail to compile with the same error https://godbolt.org/z/3nn5aKEPb

The error goes away if the span is not const https://godbolt.org/z/nEc6hY5T6 or if another type other than bool is used https://godbolt.org/z/x6GK5aqeY

[miscco]

Opened https://cplusplus.github.io/LWG/issue4520