darwin/cocoa: adding uiTab to uiGrid causes a stack overflow

[Treeki]

I'm experimenting with libui for the first time using libui-rs and have hit upon an interesting bug which, as far as I can tell from some cursory debugging, is an issue in the underlying C/ObjC libraries.

Adding uiTab to uiGrid causes a stack overflow inside the call to uiGridAppend, as illustrated in the following backtrace from lldb (with a few thousand duplicate entries removed for brevity):

    frame #7822: 0x00000001001d1fb8 libui.A.dylib`-[gridView establishOurConstraints] + 7960
    frame #7823: 0x00000001001d1fb8 libui.A.dylib`-[gridView establishOurConstraints] + 7960
    frame #7824: 0x00000001001d1fb8 libui.A.dylib`-[gridView establishOurConstraints] + 7960
    frame #7825: 0x00000001001d219f libui.A.dylib`-[gridView append:] + 127
    frame #7826: 0x0000000100001c6f tm155-tool`iui::controls::layout::LayoutGrid::append::hea401a736b5872b2(self=&0x7ffeefbfef40, _ctx=&0x7ffeefbff230, control=TabGroup {
uiTab: &0x10043c190
}, left=0, height=1, xspan=1, yspan=1, expand=Neither, halign=Fill, valign=Fill) at layout.rs:361
    frame #7827: 0x0000000100002538 tm155-tool`tm155_tool::MouseWindow::new::h476612a68b1c9009(ui=&0x7ffeefbff230) at main.rs:62
    frame #7828: 0x000000010000295a tm155-tool`tm155_tool::main::h3acaee3fc6f51bd5 at main.rs:83

I think I've found what the cause is, but I'm not familiar enough with libui to know how to fix it properly. Here is what I believe is happening:

• -[gridView append:] is called, which adds the gridChild instance (containing a uiTab) to children and then calls -[gridView establishOurConstraints]
• This calls uiDarwinControlSetHuggingPriority for all of its children
• For the uiTab child, this goes to uiTabSetHuggingPriority, which sets its priority and then calls uiDarwinNotifyEdgeHuggingChanged on itself
• This calls uiDarwinControlChildEdgeHuggingChanged on its parent, the uiGrid, which goes to uiGridChildEdgeHuggingChanged
• This function calls -[gridView establishOurConstraints]
• ... Rinse and repeat

My first guess for a fix would be to store a flag inside the gridView struct so that establishOurConstraints can't be recursively called, but I don't know if this would maintain correct behaviour.