Objective-C Headers cause dependency loop

[schroffl]

When importing objc/runtime.h and/or objc/message.h the compiler detects a dependency loop.

const objc = @cImport({
    @cInclude("objc/runtime.h");
    @cInclude("objc/message.h");
});

pub fn main() void {
    const value: objc.id = undefined;
}

---

The problem is caused by these definitions:

pub const Class = [*c]struct_objc_class;
pub const struct_objc_class = extern struct {
    isa: Class,
    super_class: Class,
    name: [*c]const u8,
    version: c_long,
    info: c_long,
    instance_size: c_long,
    ivars: [*c]struct_objc_ivar_list,
    methodLists: [*c]([*c]struct_objc_method_list),
    cache: [*c]struct_objc_cache,
    protocols: [*c]struct_objc_protocol_list,
};

which can be fixed by using @This() to reference the struct itself:

pub const struct_objc_class = extern struct {
    isa: [*c]@This(),
    super_class: [*c]@This(),
    // [...]
};

---

Another offender is this definition:

pub const struct_objc_object = extern struct {
    isa: Class,
};
pub const id = [*c]struct_objc_object;
pub const IMP = ?extern fn (id, SEL, ...) id;

A Class has a method list with IMPs, which causes the dependency loop.

Here's a hacky fix for that, but I would prefer not to loose type safety. Is there a better workaround?

pub const struct_objc_object = extern struct {
    isa: *c_void,
};

---

Edit: I am running macOS 10.14

[andrewrk]

This sounds like it will be fixed by #2174 which is still planned for this release cycle.

[schroffl]

Alright, does the *c_void fix have an consequences other than loosing type safety? Is the information relevant for linking et al.?

[andrewrk]

I believe this was fixed by #2174. Please let me know if it is not.