Why Rainbow fails on iOS 8

Last week, I received a disturbing bug report from an iOS 8 user: Rainbow, it seems, wasn't properly saving any game state. So, I sat down to see what the problem was.

The culprit seems to be the helper function user_data_dir, which is responsible for figuring out where to store data files for the game:

string user_data_dir(string const &app_name)
    /* ... */
    #elif defined(IOS)
    ret = "../Documents";
    #elif defined(ANDROID)
    /* ... */
    return ret;
}

Hmm. A hardcoded path. That seems brittle.

Looking up user data paths and iOS 8, I came across a tech note which pretty succinctly explained the situation. Basically, the Documents directory is no longer a sibling of the application, so must be requested using a (ObjC) call, which I ended up dumping into a different (compiled-as-ObjC++) file:

std::string documents_directory() {
    return [[[[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject] path] UTF8String];
}

And that seems to have done it. Expect a 1.5.2 version of Rainbow to appear soon.