[libcxx-commits] [libcxx] [libc++] Fix UB in <expected> related to "has value" flag (#68552) (PR #68733)

[Louis Dionne via libcxx-commits]

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@@ -136,14 +134,7 @@ class expected {
     noexcept(is_nothrow_copy_constructible_v<_Tp> && is_nothrow_copy_constructible_v<_Err>) // strengthened
     requires(is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Err> &&
              !(is_trivially_copy_constructible_v<_Tp> && is_trivially_copy_constructible_v<_Err>))
-      : __has_val_(__other.__has_val_) {
----------------
ldionne wrote:

I think we need a test for each of these changed functions. It should be really easy to add. For example, if we have

```
std::expected<TailClobberer<0>, bool> e = {...};
std::expected<TailClobberer<0>, bool> copy(e);
assert(copy.has_value()); // would be false before the patch, should be true after
```

https://github.com/llvm/llvm-project/pull/68733