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

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================
@@ -43,6 +44,17 @@ constexpr bool test() {
     assert(!e.has_value());
   }
 
+  // See comments of the corresponding test in
+  // "expected.expected/observers/has_value.pass.cpp".
+  {
+    const std::expected<void, TailClobberer<1>> e(std::unexpect);
+    // clang-cl does not support [[no_unique_address]] yet.
+#if !(defined(TEST_COMPILER_CLANG) && defined(_MSC_VER))
+    static_assert(sizeof(TailClobberer<1>) == sizeof(e));
+#endif
----------------
huixie90 wrote:

`[[no_unique_address]]` is a libc++ extension to `std::expected`.  
we should put this test in test/libcxx folder
(tests in test/std is meant to pass for all stl implementations)

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