Tabs: Fix MMHoverButton poor usage of images and potential stack overflow

Fix hover buttons to not keep setting image on itself everytime a fg
color is changed, leading to each image referring to the last one. If a
display changed happens and macOS triggers a redraw, this could
sometimes lead to a stack overflow crash.

Just simplify the code and properly separate out the image template and
the derived images. This also makes sure we properly free the old
images when we change fg color where we discard the last image and make
a new one.

Author: ychin

src/MacVim/MMTabline/MMHoverButton.h

@@ -5,6 +5,7 @@
 @interface MMHoverButton : NSButton
 
 @property (nonatomic, retain) NSColor *fgColor;
+@property (nonatomic, retain) NSImage *imageTemplate;
 
 typedef enum : NSUInteger {
     MMHoverButtonImageAddTab = 0,

src/MacVim/MMTabline/MMHoverButton.m

@@ -90,11 +90,12 @@ - (instancetype)initWithFrame:(NSRect)frameRect
 - (void)setFgColor:(NSColor *)color
 {
     _fgColor = color;
-    self.image = super.image;
+    [self setImageTemplate:_imageTemplate];
 }
 
-- (void)setImage:(NSImage *)imageTemplate
+- (void)setImageTemplate:(NSImage *)imageTemplate
 {
+    _imageTemplate = imageTemplate;
     _circle.cornerRadius = imageTemplate.size.width / 2.0;
     NSColor *fillColor = self.fgColor ?: NSColor.controlTextColor;
     NSImage *image = [NSImage imageWithSize:imageTemplate.size
@@ -105,16 +106,7 @@ - (void)setImage:(NSImage *)imageTemplate
         NSRectFillUsingOperation(dstRect, NSCompositingOperationSourceAtop);
         return YES;
     }];
-    NSImage *alternateImage = [NSImage imageWithSize:imageTemplate.size
-                                             flipped:NO
-                                      drawingHandler:^BOOL(NSRect dstRect) {
-        [[fillColor colorWithAlphaComponent:0.2] set];
-        [[NSBezierPath bezierPathWithOvalInRect:dstRect] fill];
-        [image drawInRect:dstRect];
-        return YES;
-    }];
-    super.image = image;
-    self.alternateImage = alternateImage;
+    self.image = image;
 }
 
 - (void)setEnabled:(BOOL)enabled

src/MacVim/MMTabline/MMTab.m

@@ -40,7 +40,7 @@ - (instancetype)initWithFrame:(NSRect)frameRect tabline:(MMTabline *)tabline
         _tabline = tabline;
 
         _closeButton = [MMHoverButton new];
-        _closeButton.image = [MMHoverButton imageFromType:MMHoverButtonImageCloseTab];
+        _closeButton.imageTemplate = [MMHoverButton imageFromType:MMHoverButtonImageCloseTab];
         _closeButton.target = self;
         _closeButton.action = @selector(closeTab:);
         _closeButton.translatesAutoresizingMaskIntoConstraints = NO;

src/MacVim/MMTabline/MMTabline.m

@@ -17,7 +17,7 @@
 
 static MMHoverButton* MakeHoverButton(MMTabline *tabline, MMHoverButtonImage imageType, NSString *tooltip, SEL action, BOOL continuous) {
     MMHoverButton *button = [MMHoverButton new];
-    button.image = [MMHoverButton imageFromType:imageType];
+    button.imageTemplate = [MMHoverButton imageFromType:imageType];
     button.translatesAutoresizingMaskIntoConstraints = NO;
     button.target = tabline;
     button.action = action;