[BUG]: thrust::optional<T&>::emplace() does not compile

[Snektron]

Is this a duplicate?

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Type of Bug

Compile-time Error

Component

Thrust

Describe the bug

A recent change in clang revealed a problem in the implementation of thrust::optional<T&>::emplace(): it's calling this->construct(), which is not available on optional<T&>. Upon further investigation it seems that calling construct() here is not the right approach, as the address that the optional holds should be changed instead. This was reported as a bug to rocThrust, but it would be nice to have a fix upstream also.

See llvm/llvm-project#90152 and ROCm/rocThrust#404. I've implemented a fix downstream here: ROCm/rocThrust#405.

How to Reproduce

0. See godbolt link below for exact reproducer
1. Construct a thrust::optional<int&> (or any other optional holding a reference).
2. Use the emplace() method
3. Compilation fails with error message

thrust/optional.h(2756): error: class "thrust::optional<int &>" has no member "construct"
      this->construct(std::forward<Args>(args)...);
            ^
          detected during instantiation of "T &thrust::optional<T &>::emplace(Args &&...) [with T=int, Args=<int &>]" at line 12 of <source>

Expected behavior

From the implementation of the other operations in thrust::optional<T&>, it seems that emplace() on optional<T&> should replace the optional's value with the address of the operand, to construct a new T&, rather than try to construct a new T.

Reproduction link

https://godbolt.org/z/359cvPso1

Operating System

No response

nvidia-smi output

No response

NVCC version

No response