Strange conflict between NSProcessInfo and NSScreen, causing segmentation fault.

[wspl]

trafficstars

I found a strange conflict issue between NSScreen and NSProcessInfo. Using both NSProcessInfo.operatingSystemVersion and UIScreen.mainScreen will cause the application to crash with "segmentation fault". But I can't imagine the relation between them.

Minimal Example:

#[macro_use]
extern crate objc;

use cocoa::{appkit::NSScreen, base::nil};
use objc::{runtime::Object};

fn main() {
    unsafe {
        let ns_process_info = class!(NSProcessInfo);
        let process_info: *mut Object = msg_send![ns_process_info, processInfo];
        // Deleting either of the following two lines will avoid the crash.
        let os_version: *const Object = msg_send![process_info, operatingSystemVersion];
        let screen = NSScreen::mainScreen(nil);
    }
}

[package]
name = "rsplg"
version = "0.1.0"
edition = "2018"

[dependencies]
cocoa = "0.24"
objc = "0.2.7"
objc-foundation = "0.1"

[madsmtm]

msg_send! has no way to know what sending the operatingSystemVersion selector to NSProcessInfo could possibly return, so when you write let os_version: *const Object, you have the responsibility to ensure that the return type is correct. When it isn't you get to keep both pieces (this is unsafe code after all).

In this case, operatingSystemVersion does not return an instance pointer (*const Object), the return type is a struct NSOperatingSystemVersion with three integers (found out by looking at C header files and the documentation).

So the correct usage would be:

use cocoa::foundation::NSInteger;

#[repr(C)]
struct NSOperatingSystemVersion {
    major_version: NSInteger;
    minor_version: NSInteger;
    patch_version: NSInteger;
}

let os_version: NSOperatingSystemVersion = msg_send![process_info, operatingSystemVersion];