On Wed, Aug 07, 2024 at 04:23:05PM -0700, Josh Steadmon wrote:
> On 2024.08.08 07:52, Mike Hommey wrote:
> > On Wed, Aug 07, 2024 at 11:21:27AM -0700, Josh Steadmon wrote:
> > > Non-C external consumers of libgit.a have to redefine the `repository`
> > > object in their own language if they want to call
> > > initialize_repository() to ensure memory for the object is allocated
> > > correctly. This is not ideal for external consumers that have no need
> > > for the entire `the_repository` object but need to call other functions
> > > from an initialized repository. Therefore, add a friendly
> > > initialize_repository() wrapper without a `the_repository` pointer.
> >
> > Technically speaking, you don't really need this.
> >
> > You can define `repository` as an opaque type in Rust:
> > ```
> > #[allow(non_camel_case_types)]
> > #[repr(C)]
> > pub struct repository([u8; 0]);
> > ```
> >
> > And define `the_repository` as an extern symbol:
> > ```
> > extern "C" {
> > pub static mut the_repository: *mut repository;
> > }
> > ```
> >
> > Mike
>
> I've actually already done a refactor for V2 that will avoid using this
> patch entirely, but thank you for the pointer. We do something similar
> to opaquely wrap configset pointers in a later patch (we use an empty
> enum there, I'm not sure whether that approach or a zero-size array is
> preferred).
An empty enum is a never type, I wouldn't recommend using it as an opaque
wrapper. It will likely lead to the compiler doing bad things.
https://rust-lang.github.io/never-type-initiative/RFC.html
`#[repr(C)]` and `[u8; 0]` are recommended by the nomicon.
https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
(the PhantomPinned wasn't there last time I saw that page)
Mike
