#[repr(C)] not necessarily compatible with C

[bjorn3]

https://spec.ferrocene.dev/types-and-traits.html#type-representation

It was discovered¹ that for MSVC compilers certain cases around ZST's and packed structs have a different memory layout than what rustc does on every platform.

Footnotes

1. https://github.com/rust-lang/rust/issues/81996 ↩

[Veykril]

This is fine for the spec as this is considered a bug in the compiler

[bjorn3]

The algorithm that ferrocene specifies doesn't match what MSVC does. So either the bug is in MSVC or in the specification. If it is considered a bug in MSVC by microsoft, it may not be fixed in MSVC anyway for back compat reasons. And if it will be fixed, old dll's compiled before the fix may be ABI incompatible if they use a type like this.

[Veykril]

I see, well it's not too relevant for us right now as windows won't be a target. But let's keep it open to track then