Avoid UB on opaque types. #1365
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autocxx generates opaque types of a given length, represented by an array of bytes. Unless autocxx is configured to use CppRef, references exist to those types, and as those references pass through C++ they may not obey Rust aliasing rules. This is the main motivation behind adopting CppRef<T>, but meanwhile, to reduce such theoretical UB, we mark the data as both MaybeUninit and UnsafeCell such that Rust makes fewer assumptions about the underlying data. Per comments, this doesn't eliminate the chance of UB.
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autocxx generates opaque types of a given length, represented by an array of bytes. Unless autocxx is configured to use CppRef, references exist to those types, and as those references pass through C++ they may not obey Rust aliasing rules. This is the main motivation behind adopting CppRef, but meanwhile, to reduce such theoretical UB, we mark the data as both MaybeUninit and UnsafeCell such that Rust makes fewer assumptions about the underlying data.
Per comments, this doesn't eliminate the chance of UB.