Attempted to fix the lack of resizable window borders by setting the NSApplication activation policy. This fixed it, and also fixed a bunch of other things, such as the application being seen as part of Terminal, lack of dock icon, lack of application menu, etc.

bleh_darwin.m

@@ -27,6 +27,15 @@ id _objc_msgSend_uint(id obj, SEL sel, uintptr_t a)
 	return objc_msgSend(obj, sel, (NSUInteger) a);
 }
 
+/*
+same as above, but for NSInteger
+*/
+
+id objc_msgSend_int(id obj, SEL sel, intptr_t a)
+{
+	return objc_msgSend(obj, sel, (NSInteger) a);
+}
+
 /*
 These are the objc_msgSend() wrappers around NSRect. The problem is that while on 32-bit systems, NSRect is a concrete structure, on 64-bit systems it's just a typedef to CGRect. While in practice just using CGRect everywhere seems to work, better to be safe than sorry.
 

objc_darwin.h

@@ -75,6 +75,7 @@ m1(sel, SEL)
 extern id _objc_msgSend_uint(id obj, SEL sel, uintptr_t a);
 m1(ptr, void *)
 m1(bool, BOOL)
+extern id objc_msgSend_int(id obj, SEL sel, intptr_t a);
 
 m2(id_id, id, id)
 extern id _objc_msgSend_rect_bool(id obj, SEL sel, int64_t x, int64_t y, int64_t w, int64_t h, BOOL b);

uitask_darwin.go

@@ -2,6 +2,7 @@
 package ui
 
 import (
+	"fmt"
 	"runtime"
 	"unsafe"
 )
@@ -66,10 +67,17 @@ var (
 	_NSApplication = objc_getClass("NSApplication")
 
 	_sharedApplication = sel_getUid("sharedApplication")
+	_setActivationPolicy = sel_getUid("setActivationPolicy:")
 )
 
 func initCocoa() (NSApp C.id, err error) {
 	NSApp = C.objc_msgSend_noargs(_NSApplication, _sharedApplication)
+	r := C.objc_msgSend_int(NSApp, _setActivationPolicy,
+		0)		// NSApplicationActivationPolicyRegular
+	if C.BOOL(uintptr(unsafe.Pointer(r))) != C.BOOL(C.YES) {
+		err = fmt.Errorf("error setting NSApplication activation policy (basically identifies our program as a separate program; needed for several things, such as Dock icon, menu, window resizing, etc.) (unknown reason)")
+		return
+	}
 	err = mkAppDelegate()
 	return
 }