[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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================
@@ -102,6 +104,22 @@ struct TrackedMove {
   }
 };
 
+// This type has one byte of tail padding where `std::expected` may put its
+// "has value" flag. The constructor will clobber all bytes including the
+// tail padding. With this type we can check that `std::expected` handles
+// the case where the "has value" flag is an overlapping subobject correctly.
+//
+// See https://github.com/llvm/llvm-project/issues/68552 for details.
+template <int c>
----------------
ldionne wrote:

```suggestion
template <int constant>
```

Maybe?

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