Set up a future system for OS X like we have on GTK+ and moved everything we already have to it. You'll notice we also set up a loader for what we're going to use this for: using OpenType attributes directly on OS X.

darwin/CMakeLists.txt

@@ -22,6 +22,7 @@ list(APPEND _LIBUI_SOURCES
 	darwin/fontbutton.m
 	darwin/fontmatch.m
 	darwin/form.m
+	darwin/future.m
 	darwin/graphemes.m
 	darwin/grid.m
 	darwin/group.m

darwin/autolayout.m

@@ -12,9 +12,7 @@ NSLayoutConstraint *mkConstraint(id view1, NSLayoutAttribute attr1, NSLayoutRela
 		attribute:attr2
 		multiplier:multiplier
 		constant:c];
-	// apparently only added in 10.9
-	if ([constraint respondsToSelector:@selector(setIdentifier:)])
-		[((id) constraint) setIdentifier:desc];
+	FUTURE_NSLayoutConstraint_setIdentifier(constraint, desc);
 	return constraint;
 }
 

darwin/future.m

@@ -0,0 +1,50 @@
+// 19 may 2017
+#import "uipriv_darwin.h"
+
+// functions and constants FROM THE FUTURE!
+
+// TODO add weight constants here?
+
+// added in OS X 10.10; we need 10.8
+CFStringRef FUTURE_kCTFontOpenTypeFeatureTag = NULL;
+CFStringRef FUTURE_kCTFontOpenTypeFeatureValue = NULL;
+
+// note that we treat any error as "the symbols aren't there" (and don't care if dlclose() failed)
+void loadFutures(void)
+{
+	void *handle;
+
+	// dlsym() walks the dependency chain, so opening the current process should be sufficient
+	handle = dlopen(NULL, RTLD_LAZY);
+	if (handle == NULL)
+		return;
+#define GET(var, fn) *((void **) (&var)) = dlsym(handle, #fn)
+	GET(FUTURE_kCTFontOpenTypeFeatureTag, kCTFontOpenTypeFeatureTag);
+	GET(FUTURE_kCTFontOpenTypeFeatureValue, kCTFontOpenTypeFeatureValue);
+	dlclose(handle);
+}
+
+// wrappers for methods that exist in the future that we can check for with respondsToSelector:
+// keep them in one place for convenience
+
+// apparently only added in 10.9; we need 10.8
+void FUTURE_NSLayoutConstraint_setIdentifier(NSLayoutConstraint *constraint, NSString *identifier)
+{
+	id cid = (id) constraint;
+
+	if ([constraint respondsToSelector:@selector(setIdentifier:)])
+		[cid setIdentifier:identifier];
+}
+
+// added in 10.11; we need 10.8
+// return whether this was done because we recreate its effects if not (see winmoveresize.m)
+BOOL FUTURE_NSWindow_performWindowDragWithEvent(NSWindow *w, NSEvent *initialEvent)
+{
+	id cw = (id) w;
+
+	if ([w respondsToSelector:@selector(performWindowDragWithEvent:)]) {
+		[cw performWindowDragWithEvent:initialEvent];
+		return YES;
+	}
+	return NO;
+}

darwin/main.m

@@ -119,6 +119,7 @@ const char *uiInit(uiInitOptions *o)
 		[realNSApp() setDelegate:delegate];
 
 		initAlloc();
+		loadFutures();
 
 		// always do this so we always have an application menu
 		appDelegate().menuManager = [[menuManager new] autorelease];

darwin/uipriv_darwin.h

@@ -2,6 +2,7 @@
 #define MAC_OS_X_VERSION_MIN_REQUIRED MAC_OS_X_VERSION_10_8
 #define MAC_OS_X_VERSION_MAX_ALLOWED MAC_OS_X_VERSION_10_8
 #import <Cocoa/Cocoa.h>
+#include <dlfcn.h>		// see future.m
 #import "../ui.h"
 #import "../ui_darwin.h"
 #import "../common/uipriv.h"
@@ -163,3 +164,10 @@ extern void openTypeToAAT(uiOpenTypeFeatures *otf, void (*doAAT)(uint16_t type,
 	(x8tox32(b) << 16) |		\
 	(x8tox32(c) << 8) |		\
 	x8tox32(d))
+
+// future.m
+extern CFStringRef FUTURE_kCTFontOpenTypeFeatureTag;
+extern CFStringRef FUTURE_kCTFontOpenTypeFeatureValue;
+extern void loadFutures(void);
+extern void FUTURE_NSLayoutConstraint_setIdentifier(NSLayoutConstraint *constraint, NSString *identifier);
+extern BOOL FUTURE_NSWindow_performWindowDragWithEvent(NSWindow *w, NSEvent *initialEvent);

darwin/winmoveresize.m

@@ -48,12 +48,10 @@ void doManualMove(NSWindow *w, NSEvent *initialEvent)
 	BOOL (^handleEvent)(NSEvent *e);
 	__block BOOL done;
 
-	// this is only available on 10.11 and newer (LONGTERM FUTURE)
-	// but use it if available; this lets us use the real OS dragging code, which means we can take advantage of OS features like Spaces
-	if ([w respondsToSelector:@selector(performWindowDragWithEvent:)]) {
-		[((id) w) performWindowDragWithEvent:initialEvent];
+	// 10.11 gives us a method to handle this for us
+	// use it if available; this lets us use the real OS dragging code, which means we can take advantage of OS features like Spaces
+	if (FUTURE_NSWindow_performWindowDragWithEvent(w, initialEvent))
 		return;
-	}
 
 	mdp.w = w;
 	mdp.initialFrame = [mdp.w frame];

unix/uipriv_unix.h

@@ -5,7 +5,7 @@
 #define GDK_VERSION_MAX_ALLOWED GDK_VERSION_3_10
 #include <gtk/gtk.h>
 #include <math.h>
-#include <dlfcn.h>		// see drawtext.c
+#include <dlfcn.h>		// see future.c
 #include <langinfo.h>
 #include <string.h>
 #include <stdlib.h>