Fix Miri Stacked Borrows violation in ffi wrapper macros#131
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The Opaque ZST wrapper (UnsafeCell<()>) used for borrowed FFI reference types caused zero-byte borrow tags under Miri's Stacked Borrows model. Any pointer derived from &StreamParamsRef (or other *Ref types) inherited this zero-byte tag, making all reads through it undefined behavior. Replace Opaque with MaybeUninit<$ctype> so each borrowed type has the same size and alignment as its underlying C type, ensuring borrow tags cover the actual data bytes. Apply the same fix to DeviceCollectionRef which used Opaque directly. Updated tests that used sentinel pointers to use valid allocations.
Pehrsons
approved these changes
Feb 9, 2026
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The Opaque ZST wrapper (UnsafeCell<()>) used for borrowed FFI reference types caused zero-byte borrow tags under Miri's Stacked Borrows model. Any pointer derived from &StreamParamsRef (or other *Ref types) inherited this zero-byte tag, making all reads through it undefined behavior.
Replace Opaque with MaybeUninit<$ctype> so each borrowed type has the same size and alignment as its underlying C type, ensuring borrow tags cover the actual data bytes. Apply the same fix to DeviceCollectionRef which used Opaque directly.
Updated tests that used sentinel pointers to use valid allocations.