MMTabline: Clear all tabs while showing / hiding tab line

When the GUI tab line is hidden (either due to `set showtabline` or `set
go-=e`), Vim stops sending update messages to the GUI. This means the
tabs were stale and would never get cleared, and the moment we show the
tabs we see a confusing animation when the tabs quicly try to rearrange
to match Vim's state. To fix this, just make sure to clean up and remove
all of them when we hide the tab line.

Author: ychin

src/MacVim/MMTabline/MMTabline.h

@@ -33,6 +33,7 @@
 - (NSInteger)addTabAtIndex:(NSInteger)index;
 
 - (void)closeTab:(MMTab *)tab force:(BOOL)force layoutImmediately:(BOOL)layoutImmediately;
+- (void)closeAllTabs;
 
 /// Batch update all the tabs using tab tags as unique IDs. Tab line will handle
 /// creating / removing tabs as necessary, and moving tabs to their new

src/MacVim/MMTabline/MMTabline.m

@@ -315,6 +315,18 @@ - (void)closeTab:(MMTab *)tab force:(BOOL)force layoutImmediately:(BOOL)layoutIm
     }
 }
 
+- (void)closeAllTabs
+{
+    _selectedTabIndex = -1;
+    _draggedTab = nil;
+    _initialDraggedTabIndex = _finalDraggedTabIndex = NSNotFound;
+    for (MMTab *tab in _tabs) {
+        [tab removeFromSuperview];
+    }
+    [_tabs removeAllObjects];
+    [self fixupLayoutWithAnimation:NO];
+}
+
 - (void)updateTabsByTags:(NSInteger *)tags len:(NSUInteger)len delayTabResize:(BOOL)delayTabResize
 {
     BOOL needUpdate = NO;
@@ -564,7 +576,13 @@ - (void)fixupTabZOrder
 
 - (void)fixupLayoutWithAnimation:(BOOL)shouldAnimate delayResize:(BOOL)delayResize
 {
-    if (_tabs.count == 0) return;
+    if (_tabs.count == 0) {
+        NSRect frame = _tabsContainer.frame;
+        frame.size.width = 0;
+        _tabsContainer.frame = frame;
+        [self updateTabScrollButtonsEnabledState];
+        return;
+    }
 
     if (delayResize) {
         // The pending delayed resize is trigged by mouse exit, but if we are

src/MacVim/MMVimView.h

@@ -44,6 +44,7 @@
 
 - (MMTabline *)tabline;
 - (IBAction)addNewTab:(id)sender;
+- (void)showTabline:(BOOL)on;
 - (void)updateTabsWithData:(NSData *)data;
 - (void)refreshTabProperties;
 

src/MacVim/MMVimView.m

@@ -251,9 +251,21 @@ - (void)setDesiredRows:(int)r columns:(int)c
 
 - (IBAction)addNewTab:(id)sender
 {
+    // Callback from the "Create a new tab button". We override this so we can
+    // send a message to Vim first and let it handle it before replying back.
     [vimController sendMessage:AddNewTabMsgID data:nil];
 }
 
+- (void)showTabline:(BOOL)on
+{
+    [tabline setHidden:!on];
+    if (!on) {
+        // When the tab is not shown we don't get tab updates from Vim. We just
+        // close all of them as otherwise we will be holding onto stale states.
+        [tabline closeAllTabs];
+    }
+}
+
 /// Callback from Vim to update the tabline with new tab data
 - (void)updateTabsWithData:(NSData *)data
 {

src/MacVim/MMWindowController.m

@@ -868,7 +868,7 @@ - (void)processInputQueueDidFinish
 
 - (void)showTabline:(BOOL)on
 {
-    [[vimView tabline] setHidden:!on];
+    [vimView showTabline:on];
     [self updateTablineSeparator];
     shouldMaximizeWindow = YES;
 }