Merge pull request #857 from ychin/pre-mojave-scrollbar-render-fix

Fix scrollbar rendering artifact in pre-Mojave renderer

Author: ychin

src/MacVim/MMVimView.m

@@ -929,7 +929,19 @@ - (void)frameSizeMayHaveChanged:(BOOL)keepGUISize
     NSRect textViewRect = [self textViewRectForVimViewSize:[self frame].size];
     [textView setFrame:textViewRect];
 
-    self.pendingPlaceScrollbars = YES;
+    // Immediately place the scrollbars instead of deferring till later here.
+    // Deferral ended up causing some bugs, in particular when in <10.14
+    // CoreText renderer where [NSAnimationContext beginGrouping] is used to
+    // bundle state changes together and the deferred placeScrollbars would get
+    // the wrong data to use. An alternative would be to check for that and only
+    // call finishPlaceScrollbars once we call [NSAnimationContext endGrouping]
+    // but that makes the code mode complicated. Just do it here and the
+    // performance is fine as this gets called occasionally only
+    // (pendingPlaceScrollbars is mostly for the case if we are adding a lot of
+    // scrollbars at once we want to only call placeScrollbars once instead of
+    // doing it N times).
+    self.pendingPlaceScrollbars = NO;
+    [self placeScrollbars];
 
     // It is possible that the current number of (rows,columns) is too big or
     // too small to fit the new frame.  If so, notify Vim that the text