wit-bindgen-rust: fix lowering and lifting of zero-length lists. #296
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This commit fixes the Rust bindings generated for lifting and lowering of lists to account for lists of zero-length. It is undefined behavior to call `std::alloc::alloc` with a zero-sized layout. Additionally, as the behavior of the `canonical_abi_realloc` implemented in `wit-bindgen` is to return a non-null dummy pointer for a zero-sized alloc, the bindings were calling `std::alloc::dealloc` with a pointer that was not allocated with `std::alloc::alloc` (also undefined behavior). To fix this, the bindings now account for zero-length lists and skip allocation and deallocation where appropriate.
alexcrichton
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Aug 3, 2022
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Would it be possible to add some tests exercising this as well which try to transfer empty lists or nonempty lists of zero-sized types? (also perhaps empty strings?)
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This PR fixes the Rust bindings generated for lifting and lowering of lists
to account for lists of zero-length.
It is undefined behavior to call
std::alloc::allocwith a zero-sized layout.Additionally, as the behavior of the
canonical_abi_reallocimplemented inwit-bindgenis to return a non-null dummy pointer for a zero-sized alloc, thebindings were calling
std::alloc::deallocwith a pointer that was notallocated with
std::alloc::alloc(also undefined behavior).To fix this, the bindings now account for zero-length lists and skip allocation
and deallocation where appropriate.