Add IsOverlapped implementation for macOS.

ui/platform/mac/ui_utility_mac.mm

@@ -103,7 +103,55 @@ void IgnoreAllActivation(not_null<QWidget*> widget) {
 std::optional<bool> IsOverlapped(
 		not_null<QWidget*> widget,
 		const QRect &rect) {
-	return std::nullopt;
+	NSWindow *window = [reinterpret_cast<NSView*>(widget->window()->winId()) window];
+	Assert(window != nullptr);
+
+	if (![window isOnActiveSpace]) {
+		return true;
+	}
+
+	const auto nativeRect = CGRectMake(
+		rect.x(),
+		rect.y(),
+		rect.width(),
+		rect.height());
+
+	CGWindowID windowId = (CGWindowID)[window windowNumber];
+	const CGWindowListOption options = kCGWindowListExcludeDesktopElements
+		| kCGWindowListOptionOnScreenAboveWindow;
+	CFArrayRef windows = CGWindowListCopyWindowInfo(options, windowId);
+	if (!windows) {
+		return std::nullopt;
+	}
+	const auto guard = gsl::finally([&] {
+		CFRelease(windows);
+	});
+	NSMutableArray *list = (__bridge NSMutableArray*)windows;
+	for (NSDictionary *window in list) {
+		NSNumber *alphaValue = [window objectForKey:@"kCGWindowAlpha"];
+		const auto alpha = alphaValue ? [alphaValue doubleValue] : 1.;
+		if (alpha == 0.) {
+			continue;
+		}
+		NSString *owner = [window objectForKey:@"kCGWindowOwnerName"];
+		NSNumber *layerValue = [window objectForKey:@"kCGWindowLayer"];
+		const auto layer = layerValue ? [layerValue intValue] : 0;
+		if (owner && [owner isEqualToString:@"Dock"] && layer == 20) {
+			// It is always full screen.
+			continue;
+		}
+		CFDictionaryRef bounds = (__bridge CFDictionaryRef)[window objectForKey:@"kCGWindowBounds"];
+		if (!bounds) {
+			continue;
+		}
+		CGRect rect;
+		if (!CGRectMakeWithDictionaryRepresentation(bounds, &rect)) {
+			continue;
+		} else if (CGRectIntersectsRect(rect, nativeRect)) {
+			return true;
+		}
+	}
+	return false;
 }
 
 TitleControls::Layout TitleControlsLayout() {