Marker types should be FFI-safe

[steveklabnik]

Issue by mzabaluev
Wednesday Oct 01, 2014 at 09:56 GMT

For earlier discussion, see rust-lang/rust#17679

This issue was labelled with: in the Rust repository

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If I get a struct by pointer from a foreign library, and I know the structure cannot safely be copied because the actual object is larger than the struct, I want to declare it as something like this:

#[repr(C)]
struct A {
    // ...
    no_copy: std::kinds::marker::NoCopy;
}

Now the compiler complains at use site that the struct is not foreign-function-safe.
As the markers are zero-sized, they have no bearing on the layout and no consequences for the structure data, so they, as long as any other zero-sized structures, should not waive FFS.

@thestinger suggests the same should apply to structures with one field as well, but I'm not so certain about that: there could be optimizations regarding alignment which would not be compatible with the (default) C ABI.

[mbrubeck]

See also #750.

[Centril]

std::kinds::marker::NoCopy does not exist so I am closing this.