Create assert_field_offsets! macro
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Right now, it cannot be implemented soundly. It needs both rust-lang/rust#63810 and rust-lang/rust#64588, as well as allowing |
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This introduces
assert_field_offsets!for ensuring that givenstructfields are at specific offsets.This current implementation works in Rust 1.37 and 1.38. However, the current beta and nightly compilers fail to perform the constant evaluation. This is not unexpected since the current code creates a reference at
mem::align_of::<T>(), where there is no initialized memory. Even though the reference is non-null, dereferencing those addresses is definitely undefined behavior.I won't be merging this PR as-is. However, I'm interested to learn how this macro could be implemented in a sound way.
See also: Gilnaa/memoffset#24.
(cc @oli-obk @RalfJung)