My setup is like this:
From a WDL/SWELL main application (only a wrapper) I'm creating an SDL window on macOS - therefore an instance of SDLApplication is not being set.

After polling event with SDL_PollEvent,
SDL_KEYDOWN, and SDL_KEYUP are not being called.
You can force it to call if you smash the keyboard and it gets some keystrokes here and there.

SDL_GetModState() returns always zero and SDL_GetKeyboardState(NULL) never changes.

Debugging this, leads me to the problematic line:
SDL_cocoaevents.m:
NSEvent *event = [NSApp nextEventMatchingMask:NSEventMaskAny untilDate:[NSDate distantPast] inMode:NSDefaultRunLoopMode dequeue:YES ];

if we change it to 
NSEvent *nextDown = [NSApp nextEventMatchingMask:NSEventMaskAny untilDate:[NSDate dateWithTimeIntervalSinceNow:0.01] inMode:NSDefaultRunLoopMode dequeue:YES];

After this, it started work, but it's too much time waiting there polling the event. I was looking everywhere what could be dequeuing this event. 

Eventually I have found the SDLWindow class, in SDL_cocoawindow.m.
It has the same callback as SDLApplication - sendEvent. It receives all the keystrokes in time like a charm. from there I'm pushing it back to SDL's pipe by calling Cocoa_DispatchEvent(event).

It looks that the key handling events is on the NSApplication (SDLApplication) and not on the NSWindon (SDLWindow)


here's my working patch (needs a bit of tidying):
https://github.com/amiramitai/SDL-mirror/commit/5b5b818795e39b751c65b8e6c9bd908a4a0df853