Fix MMTouchBarButton warning when calling "desc" function

Refactor the code so that the relevant class is in header and can be
called. Also fix different places where I call NSClassFromString to use
@available check instead, as I believe that's the recommended method and
more efficient as well (due to it being native to the compiler).

Author: ychin

src/MacVim/MMVimController.h

@@ -15,6 +15,16 @@
 @class MMTouchBarInfo;
 
 
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12
+/// Button used for Touch Bar support, with an additional metadata to store the
+/// Vim command it should send.
+@interface MMTouchBarButton : NSButton {
+    NSArray *_desc;
+}
+- (NSArray *)desc;
+- (void)setDesc:(NSArray *)desc;
+@end
+#endif
 
 @interface MMVimController : NSObject<
     NSToolbarDelegate

src/MacVim/MMVimController.m

@@ -102,13 +102,6 @@ - (id)initWithItem:(NSTouchBarItem *)item label:(NSString *)label;
 - (void)setTouchBarItem:(NSTouchBarItem *)item;
 - (void)makeChildTouchBar;
 @end
-
-@interface MMTouchBarButton : NSButton {
-    NSArray *_desc;
-}
-- (NSArray *)desc;
-- (void)setDesc:(NSArray *)desc;
-@end
 #endif
 
 @interface MMVimController (Private)
@@ -183,7 +176,7 @@ - (id)initWithBackend:(id)backend pid:(int)processIdentifier
     popupMenuItems = [[NSMutableArray alloc] init];
     toolbarItemDict = [[NSMutableDictionary alloc] init];
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12_2
-    if (NSClassFromString(@"NSTouchBar")) {
+    if (@available(macos 10.12.2, *)) {
         touchbarInfo = [[MMTouchBarInfo alloc] init];
     }
 #endif
@@ -1221,7 +1214,7 @@ - (void)addMenuWithDescriptor:(NSArray *)desc atIndex:(int)idx
 
     if ([rootName isEqual:MMTouchbarMenuName]) {
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12_2
-        if (NSClassFromString(@"NSTouchBar")) {
+        if (@available(macos 10.12.2, *)) {
             if ([desc count] < 2) // Cannot be 1, as we need at least TouchBar.<menu_name>
                 return;
             if ([desc count] >= 3) // Unfortunately currently Apple does not support nested popover's so we can only do one level nesting
@@ -1305,7 +1298,7 @@ - (void)addMenuItemWithDescriptor:(NSArray *)desc
         if ([desc count] >= 4) // Unfortunately currently Apple does not support nested popover's so we can only do one level nesting
             return;
 
-        if (NSClassFromString(@"NSTouchBar")) {
+        if (@available(macos 10.12.2, *)) {
             MMTouchBarInfo *submenuTouchbar = nil;
             if (![self touchBarItemForDescriptor:desc touchBar:&submenuTouchbar touchBarItem:nil]) {
                 return;
@@ -1388,7 +1381,7 @@ - (void)removeMenuItemWithDescriptor:(NSArray *)desc
     }
     if ([rootName isEqual:MMTouchbarMenuName]){
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12_2
-        if (NSClassFromString(@"NSTouchBar")) {
+        if (@available(macos 10.12.2, *)) {
             MMTouchBarInfo *submenuTouchbar = nil;
             if (![self touchBarItemForDescriptor:desc touchBar:&submenuTouchbar touchBarItem:nil]) {
                 return;
@@ -1442,7 +1435,7 @@ - (void)enableMenuItemWithDescriptor:(NSArray *)desc state:(BOOL)on
 
     if ([rootName isEqual:MMTouchbarMenuName]) {
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12_2
-        if (NSClassFromString(@"NSTouchBar")) {
+        if (@available(macos 10.12.2, *)) {
             MMTouchBarItemInfo *touchbarItem = nil;
             if (![self touchBarItemForDescriptor:desc touchBar:nil touchBarItem:&touchbarItem]) {
                 return;
@@ -1481,7 +1474,7 @@ - (void)updateMenuItemTooltipWithDescriptor:(NSArray *)desc
 
     if ([rootName isEqual:MMTouchbarMenuName]) {
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12_2
-        if (NSClassFromString(@"NSTouchBar")) {
+        if (@available(macos 10.12.2, *)) {
             MMTouchBarItemInfo *touchbarItem = nil;
             if (![self touchBarItemForDescriptor:desc touchBar:nil touchBarItem:&touchbarItem]) {
                 return;

src/MacVim/MMWindowController.m

@@ -1114,7 +1114,8 @@ - (IBAction)vimToolbarItemAction:(id)sender
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_12_2
 - (IBAction)vimTouchbarItemAction:(id)sender
 {
-    NSArray *desc = [sender desc];
+    MMTouchBarButton *button = (MMTouchBarButton*)sender;
+    NSArray *desc = [button desc];
     NSDictionary *attrs = [NSDictionary dictionaryWithObject:desc
                                                       forKey:@"descriptor"];
     [vimController sendMessage:ExecuteMenuMsgID data:[attrs dictionaryAsData]];